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Detailed explanations in West Bengal Board Class 10 Physical Science Book Solutions Chapter 8.3 Electricity and Chemical Reactions offer valuable context and analysis.

WBBSE Class 10 Physical Science Chapter 8.3 Questionuestion Answer – Electricity and Chemical Reactions

Very Short Answer Type Questions

Question 1.
Which agent conducts electricity through an electrolyte ?
Answer:
Ions conduct electricity through an electrolyte.

Question 2.
What is a Voltameter ?
Answer:
Voltameter is a vessel in which electrolysis is carried out.

Question 3.
What is function of acid or alkali mixed in water during electrolysis of water ?
Answer:
Acid or alkali increases number of ions that help electrolysis.

Question 4.
Name two electrolytes
Answer:
Aqueous solution of sulphuric acid (H₂SO₄), aqueous solution of sodium chloride (NaCl)

Question 5.
Name two non-electrolytes.
Answer:
Sugar solution, glycerine are two non-electrolytes.

Question 6.
What type of particles flow during electrolysis ?
Answer:
Positive and negative ions flow during electrolysis.

Question 7.
What are the electrodes used in the extraction of aluminium ?
Answer:
The carbon-lined iron tank is made the cathode and the anode is a set of carbon rods used in extraction of aluminium.

Question 8.
What is an ion ?
Answer:
Ion is an atom or radical carrying electric charge.

Question 9.
What is ionic dissociation ?
Answer:
The decomposition process of electrolytes into ions is known as ionic dis­sociation.

Question 10.
How does an atom convert to ion ?
Answer:
An atom converts to an ion either by losing or by gaining electron.

Question 11.
Which is more stable atom or ion ?
Answer:
Ion is more stable than atom.

Question 12.
What is the function of electric current in electrolysis ?
Ans.
The electric current sent into an electrolyte from a battery or any other external source only separates the two types of ions, it does not ionize the electrolyte.

Question 13.
In which state an electrolytic substance should exist during electrolysis ?
Answer:
During electrolysis an electrolytic substance should be fused state or in the state of aqueous solution.

Question 14.
What is cathode ?
Answer:
The electrode connected to the negative terminal of battery is called cathode.

Question 15.
What is anode ?
Answer:
The electrode connected to the positive terminal of battery is called anode.

Question 16.
What are cations ?
Answer:
The positive ions that move to the cathode are known as cations.

Question 17.
What are anions ?
Answer:
The negative ions that move to the anode are known as anions.

Question 18.
Which one is electrolyte ? – gold, mercury, common salt.
Answer:
Common salt is an electrolyte.

Question 19.
A brass spoon is to be nickel plated. Which is to be used as anode and which is to used as cathode ?
Answer:
Anode : Pure metal plate or rod of nickel.
Cathode : The brass spoon.

Question 20.
Name a substance which is a good conductor but not an electrolyte.
Answer:
Graphite is a good conductor but not an electrolyte.

Question 21.
Name a metal and a non-metal which can be used as electrodes.
Answer:
Metal : Platinum.
Non-metal : Graphite.

Question 22.
Is mercury an electrolyte ?
Answer:
Mercury is a good conductor but not electrolyte.

Question 23.
What is the meaning of ‘ion’ ?
Answer:
Ion’ has been derived from a Greek word meaning ‘wanderer’ or ‘traveller’ because the ions in a solution move about constantly in a random manner.

Question 24.
Between H^A and Ag^A which one will be discharged first at cathode ?
Answer:
Between H^⊕ and Ag^⊕, Ag^⊕ will be discharged first at cathode as the position of Ag^⊕ is below the position of H^⊕  in electro chemical series.

Question 25.
What is the nature of mercury ?
Answer:
Mercury is good conductor of electricity.

Question 26.
In electrolysis which energy is converted into which energy ?
Answer:
In electrolysis, electrical energy is converted into chemical energy.

Question 27.
Between Br^– and OH^– which ion will be discharged first at anode ?
Answer:
Between Br^– and OH^–, OH^– ion will be discharged first at anode as the position of OH^– ion is lower than that of Br in electrochemical series.

Question 28.
State one strong electrolyte.
Answer:
Strong electrolyte is H₂SO₄.

Question29.
Name one weak electrolyte.
Answer:
Acetic acid is an example of weak electrolyte.

Question 30.
What is called fluorspar ?
Answer:
CaF₂ is called flurospar.

Question 31.
What is called cryolite ?
Answer:
AlF₃, 3NaF is called cryolite.

Question 32.
In electrolysis of acidified water dilute sulphuric acid is preferred to dilute nitric acid or acidification. Explain.
Answer:
Both the acids may be used for acidification but dilute nitric acid is volatile and hence, less preferred compared to dilute sulphuric acid.

Question 33.
Write two applications of electrolysis in which the anode diminishes in mass.
Answer:
Electroplating of an article and electrorefining of metals.

Question 34.
Name a liquid which is non-electrolyte.
Answer:
Ethyl alcohol

Question 35.
What kind of particles will be found in a liquid compound which is a non-electrolyte?
Answer:
molecules.

Question 36.
Which one among OH^Θ or Na^⊕ will be discharged at anode?
Answer:
Anions are discharged at anode. Hence OH^Θ will be discharged at anode.

Question 37.
Name a liquid which conducts electricity but is not an electrolyte.
Answer:
Liquid metal mercury (Hg).

Question 38.
What do you mean by electrometallurgy?
Answer:
Electrometallurgy is the process of extraction of metals (which are at the top of electro chemical series) by electrolysis.

Question 39.
Name two metals other than aluminium which are extracted by electrolysis.
Answer:
Sodium (Na) and Magnesium (Mg) are extracted by the electrolysis of their molten chlorides with iron as cathode and graphite as anode.

Question 40.
What is used as anode and cathode during electrorefining of copper?
Answer:
Thin strip (or plate or wires) of pure copper is used as cathode and impure copper is used as anode during electrorefining of copper.

Question 41.
In case of electroplating of silver what is used as the electrolyte?
Answer:
Potassium argentocyanide K(Ag(CN)₂] is used as the electrolyte in case of electroplating of gold.

Short Answer Type Questions     

Question 1.
What is called Electrochemistry ?
Answer:
Electrochemistry : It is the branch of chemistry which deals with the relationship between chemical energy and electrical energy and how one can be converted into another.

Question 2.
What are Electrochemical reactions ?
Answer:
Electrochemical reactions : Oxidation and reduction-the loss and gain of electrons occur in many chemical reactions. When these reactions can be made to cause electrons to flow through a wire or when a flow of electrons makes a redox reaction happen, the reactions are known as electrochemical reactions.

Question 3.
What are Conductors ?
Answer:
Conductors : A substance which allows the electric current to flow through it is called a conductor, e.g. Cu, Ag, Al etc.

Question 4.
What are Non-conductors ?
Answer:
Non-conductors : A substance which does not allow the electric current to flow through it is called a non-conductor, e.g. wood, glass, rubber etc.

Question 5.
What are Metallic conductors ?
Answer:
Metallic conductors These are the substances (metals) which allow the current to pass through them but do not undergo any change in themselves, e.g. Cu, Ag, Au etc.

Question 6.
What are Non-metallic conductors ?
Answer:
Non-metallic conductors These are the substances (non-metals) which allow the current to pass through them but do not undergo any change in themselves, e.g. Graphite, gas-carbon etc.

Question 7.
What are Electrolytic conductors or Electrolytes ?
Answer:
Electrolytic conductor or electrolytes : These are compounds which in the fused state on in solution in a suitable solvent (particularly water) conduct an electric current and undergo distinct chemical decomposition during the process of conducting current. e.g. aque­ous solution of H₂SO₄, NaOH, NaCl etc.

Question 8.
What are Non-electrolytes ?
Answer:
Non-electrolytes : These are substances which do not conduct electricity either in solution or in molten state, e.g. solutions of sugar, urea etc. or liquids like kerosine, alcohol etc.

Question 9.
Why is mercury considered as non-electrolyte ?
Answer:
Explanation: Mercury is a liquid metal. It conducts electricity but during passage of electric current, it is not decomposed. So it is considered as non-electrolyte.

Question 10.
What is Electrolysis ?
Answer:
Electrolysis : The process of chemical decomposition of an electrolyte in solution or in fused state by the passage of electric current is called electrolysis.

Question 11.
State two points of difference between conduction of electricity through a metallic conductor and through an electrolytic substance.
Answer:
Difference between conduction of electricity through metals (also non-metals like graphite, gas carbon) and electrolytes.

Metals (also non-metals like graphite, gas carbon)	Electrolytes
(i)  Metals conduct electricity in solid state, except liquid mercury. (ii) Passage of electricity through these causes physical changes like, heating increase of electrical resistance.	(i)  Electrolytes conduct electricity in solution or in used states. (ii) Electricity through these causes chemical decomposition, which is a chemical change.

Question 12.
What are called Electrodes?
Answer:
Electrodes : The two metallic or graphite strips or rods, placed in a voltameter to pass electric current through the electrolyte during electrolysis are known as electrodes.

Question 13.
What is called Electrolytic dissociation?
Answer:
Electrolytic dissociation : The spliting up of an electrolyte into ions is known as electrolytic dissociation. This is a reversible process. This means that the electrolyte molecules break up partly into ions and the ions in solution constantly reunite to form the undissociated molecules.

Question 14.
Why pure water does not conduct electricity? In what condition does it conduct electricity ?
Answer:
Explanation : In an electrolyte, positive and negative ions conduct elec­tricity. Pure water is a very weak electrolyte in which a very small number of water molecules remain dissociated into H^⊕ and OH^– ions which can conduct electricity. That is why pure water does not conduct electricity.
Condition : To increase conductivity of water a few drops of H₂SO₄ or an alkali or small amount of NaCl is mixed with it so that positive and negative ions, the carrier of electricity, increase.

Question 15.
What is Electrolytic conduction ?
Answer:
Electrolytic conduction : The movement of ions towards oppositely charged electrodes is known as electrolytic conduction.

Question 16.
In electrolysis of water which material are the electrodes made of? Write down the reaction occuring in the electrolyte before electrolysis. Also write down the reactions taking place at cathode and anode during electrolysis.
Answer:
Electrolysis of water :
(i) Electrodes used : Both electrodes (cathode and anode) Pt.
(ii) Name of electrolytes : Water acidified with a few drops of H₂SO₄

Question 17.
Illustrate the process of electrolysis of aqueous copper sulphate solution (using Pt-electrode).
Answer:
Electrolysis of aqueous CuSO₄ (using Pt-electrode) :
Electrodes : Pt (both)
Electrolytes : Aqueous solution of CuSO₄

Question 18.
Illustrate the process of electrolysis of aqueous copper sulphate solution (using Cu, attackable electrodes).
Answer:
Electrolysis of aqueous CuSO₄ (using Cu, attackable electrodes)
(i) Electrodes : Cu(both)
(ii) Electrolytes : Aqueous solution of CuSO₄
(iii) Before electrolysis :

(iv) During electrolysis :
At cathode : Cu²⁺ + 2e → Cu↓
At anode : Cu – 2e → Cu²⁺
As a result, anode Cu-plate goes on losing its weight while that of cathode Cu-plate goes of gaining its weight. The concentration of CuSO₄, solution (electrolyte) in voltameter remains the same.

Question 19.
How cations and anions are discharged at their respective electroles ?
Answer:
The arrangement of cations discharged at cathode (according to electro chemical series)

The arrangement of anions discharged at anode (according to electrochemical series)

Question 20.
What is electroplating ? What is its aim ?
Answer:
Electroplating : It is an art of depositing a superior metal like gold, silver etc. on baser metals like iron, copper etc. through electrolysis.
Aim of electroplating :

• Decoration
• Repairs
• Protection

Question 21.
What are the conditions for good deposit ?
Answer:
Conditions for good deposit :

• High current density
• Low temperature
• High metal concentration in electrolyte
• Electrolyte must be complex salt of the metal to be deposited.

Question 22.
What are the application of electrolysis ?
Answer:
Application of electrolysis :

• Electroplating
• Electro-refining of metals
• Electro-typing
• Extraction of metals

Question 23.
Explain electroplating of Zn.
Answer:
Electroplating of Zn :
Electrolyte : ZnCl₂ solution
\(\mathrm{ZnCl}_2 \rightleftharpoons \mathrm{Zn}^{2+}+2 \mathrm{Cl}^{(-)}\)
Electrodes :
(a) Cathode : the article is to be electroplated
(b) Anode : pure Zn-rod or plate
Reaction at Cathode : Zn²⁺ + 2e → Zn↓

Question 24.
Explain electroplating of Cr.
Answer:
Electroplating of Cr :
(i) Electrolyte :

(ii) Electrodes :
(a) Cathode : the articles is to be electroplated.
(b) Anode : pure Cr-plate
(iii) Reaction at cathode : Cr³ + 3e → Cri↓

Question 25.
Explain electroplating of Sn.
Answer:
Electroplating of Sn :
Electrolyte :

Electrodes :
(a) Cathode : the article is to be electroplated
(b) Anode : pure Sn-plate
Reaction at cathode : Sn² + 2e → Sn↓

Question 26.
Explain electroplating of Cu.
Answer:
Electroplating of Cu :
Electrolyte :

Electrodes :
(a) Cathode : the article is to be electroplated
(b) Anode : pure Cu-plate
Reaction at cathode : Cu²⁺ + 2e → Cu↓

Question 27.
Explain electroplating of Ag.
Answer:
Electroplating of Ag :
Electrolyte: Potassium argentocyanide solution K[Ag(CN)₂]

Electrodes :
(a) Cathode : the article is to be electroplated
(b) Anode : pure Ag plate
Reaction at Cathode : Ag⁺ + e → Ag↓

Question 28.
Explain electroplating of Au (gold).
Answer:
(i) Electroplating of Au :
(ii) Electrolyte : Potassium aurocyanide K[Au(CN)₂] solution ;

Electrodes :
(a) Cathode : the article is to be electroplated,
(b) Anode : pure Au plate
(iii) Reaction at cathode : Au⁺ + e → Au↓

Question 29.
Explain electroplating of Ni.
Answer:
(i) \(\mathrm{NiSO}_4 \rightleftharpoons \mathrm{Ni}^{2+}+\mathrm{SO}_4^{2-}\)
(ii) Electrodes :
(a) Cathode : the article is to be electroplated
(b) Anode : pure Ni-plate
(iii) Reaction at Cathode : Ni² + 2e → Ni↓

Question 30.
How is copper purified by electrolysis method ?
Answer:
Purification of copper by electrolysis method :
Electrolyte : 15% CuSO₄ solution (aqueous) containing (5-10)% sulphuric acid at 50°C is taken in a voltameter.

Electrodes :
(a) Cathode : pure thin copper plate
(b) Anode : thick impure copper plate

Electrolysis : On electrolysis, copper dissolves from the anode and deposits on cathode. Thus gradually the anode plate wear out and the cathode plate thicken. The copper obtained in the way 99 99% purity.

Reactions : \(\mathrm{CuSO}_4 \rightleftharpoons \mathrm{Cu}^{2+}+\mathrm{SO}_4^{2-}\)
At cathode : Cu²⁺ + 2e → Cu↓
At anode : Cu → 2e Cu²⁺

Question 31.
How is aluminium extracted from electrolysis method ?
Answer:
Extraction of a luminium by electrolysis method :

Electrolytes :
(a) Alumina (Al₂O₃) 20%
(b) Fused cryolite (A1F_B, 2NaF) 60%
(c) CaF₂ 20%

Electrodes :
(a) Cathode : inner lining of carbon of the steel tank
(b) Anode : thick carbon rod suspended into fused electrolyte

Reactions :
(a) At cathode : Al³ + 3e → Al↓
(b) At anode : 3F – 3e → 3F
Al₂O₃ + 6F → 2AlF_S + 3O
6O→ 3O₂↑

Question 32.
Explain why blocks of magnesium are often strapped to the steel hulls of ocean going ships.
Answer:
Explanation: Magnesium due to lower reduction potential does not allow the oxidation of steel hulls i.e. magnesium acts, by cathodic protection to prevent oxidation of the steel by transfering an excess of electrons to the steel.

Question 33.
Sodium reacts with water at ordinary temperature while magnesium reacts with hot water. Give reason.
Answer:
Reason : Sodium being more electro-positive decomposes cold water but magnesium which is less electropositive is decomposed by hot water.

Question 34.
A silver wire is dipped in a solution CuSO₄ in one vessel, while in another vessel, a copper wire is dipped in a solution of AgNO_s. What reactions if any take place in the two vessels ?
Answer:
Explanation :
No reaction will take place in first vessel because Ag has greater reduction potential than Cu.
In second vessel, copper will displace Ag from AgNO₃ and the solution of Cu²⁺ ions
Reaction : Cu + 2Ag⁺ → Cu²⁺ + 2Ag↓

Question 35.
Which of the two is a better conductor and why?
(a) a strong electrolyte
(b) a metal.
Answer:
Explanation : Conductivity of electrolytes is due to ionic mobility while that of metal is due to the movement of electrons. Due to their negligible mass, electrons are better conductors than ions with comparatively large mass. Therefore metals are better conductors than electrolytes.

Question 36.
What is cathodic reduction ? Give one example.
Answer:
Cathodic reduction : The reduction of ions taking place at a cathode of a cell is known as cathode reduction. Example : Reduction of Cu²⁺ ions to Cu at cathode of Daniell cell is an example of cathodic reduction.

Question 37.
Anhydrous HCl is a bad conductor of electricity but aqueous HCl is a good conductor. Why ?
Answer:
Expiation : Being covalent in nature, anhydrous HCl is a bad conductor. However, in aqueous solution, it ionises to give H^⊕ and Cu^– ions which conduct the electricity.

Broad Answer Type Questions 

Question 1.
What are the main points of difference between the metallic conductors an electrolytic conductors?
Answer:
Difference between the metallic conductors and electrolytic conductors :

Metallic conductor

• A metallic conductor has relatively free electrons to move and as such the metallic conduction is caused by the flow of electrons in the conductor.
• The passage of an electric current through a metallic conductor does not involve any transfer of matter.
• A metallic conduction is not accompanied by any chemical change of conduction.

Electrolytic conductor

• Electricity is transported through an electrolyse in a state of fusion or solution not by flow of electrons but by the movement of electrically changed ions.
• Flow of electricity is due to the movement of ions and hence there is transfer of matter.
• An electrolytic conduction is invariably accompanied by chemical changes at the electrodes.

Question 2.
What changes are taking place during the electrolysis of an electrolyte?
Answer:
Changes taking place during the electrolysis of an electrolyte.

• When fused or dissolved in water, electrolyte splits up into oppositely charged particles called ions.
• On passing electric current, the cations migrate towards the cathode while the anions migrate towards the anode.
• The cations on reaching the cathode gain electrons from it and from neutral atoms which get deposited on the cathode.
• The anions on reaching the anode lose electrons and get converted into neutral atoms which may be collected as such or they may undergo some secondary change to from some other products.

 

 

Comprehensive WBBSE Class 10 Physical Science Notes Chapter 6 Current Electricity can help students make connections between concepts.

Current Electricity Class 10 WBBSE Notes

Electric current: Electric current is generally means a continuous flow of electrons, ions or any electrically charged particles through a medium.

Electric current is the rate of flow of charge through any cross-section of a canductor.

\(\left(I = \frac{Q}{t}\right)\)

(I = electric current, Q = total charge flowing, t = time)

Units of electric unit

SI unit : Ampere (A): One ampere of electric current is defined as the one coulomb of charge flowing through any cross section of a conductor in one second.

Nature of electric current: Although electric current has both magnitude and direction, yet it is a scalar quantity, as it does not obey vector laws.

Different types of electric currents are:

Steady direct current: An electric current is called a steady direct current if its magnitude and direction do not change with time.

Variable direct current : An electric current is called variable direct current if its magnitude changes with time but direction remains unchanged.

Alternating current : An electric current is called alternating current if its magnitude changes with time and direction also changes periodically.

Current denisity: Current density of a conductor is the amount of current passing per unit area of the conductor held perpendicular to the flow of charges.

Drift velocity: It is the average velocity with which free electrons in a conductor get drifted in a direction opposite to the direction of the applied electric field.

Mobility of the charge carrier: The ratio of the drift velocity of the electrons or charge carriers and the strength of the applied electric field is called the mobility of the charge carrier.

Canductor: The substances through which electric charge flows easily are known as conductors.

Non-conductor: The substances which do not allow electric charge to pass through them are called non-conductors or insulators.

Electric cell : A device in which electric energy is obtained from the chemical energy is known as electric cell.

Negative electrode: The metal rod in which there is excess of negative charge is called negative electrode of cell.

Positive electrode: The metal rod in which there is excess of positive charge is called positive electrode.

Open circuit: When the electrodes of a cell are not connected by a conductor externally, the cell is said to be in open circuit.

Close circuit: When the electrodes are connected internally with a conductor, the cell is said to be in closed circuit.

Electromotive force (e.m.f): The potential difference between the electrodes of a cell in open circuit is called e.m.f.

Potential difference : It is the electrical condition of a point in an electric field or on a current carrying conductor that indicates whether electrons will flow from it or it from another connected point.

Electrical charge: It is the physical property of a matter that causes it to experience a force when placed near another matter.

When ebonite rod is rubbed with flannel, ebonite rod is negatively charged and at the same time flannel acquires an equal amount of positive change. When a glass rod is rubbed with silk, glass rod is positively charged and the same time the silk acquires an equal amount of negative charge.

Electrostatic series: There is a list of substances called electrostatic series, which roughly shows that the two bodies when selected for rubbing will be charged in such a way that the body appearing earlier in the list is positively charged and that coming later in the list is negatively charged. The series is :
Silk, Human body, Cotton, Wood, Sealing wax, Amber, Resin, Sulphur, Rubber, Ebonite.

Basic properties of electric charge :

• Charges are of two types – positive and negative.
• Like charges repeal each other and unlike charges attract each other.
• The positive and negative charges tend to cancel each other.

Coulomb’s Law: The force between two point charges at rest is directly proportional to the product of the magnitude of the charges and inversely proportional to the square of the distance between them. The force acts along the line joining the two charges and its value depends on the nature of the intervening medium.

\(F \infty \frac{q₁ q}{r^2} or } F = K \frac{q₁ q₂}{r^2}\)

(K = electrostatic force constant or Coulomb’s constant and depends upon the system of units and the medium intervening the charges)

Validity for coulomb’s law :

• It holds basically for the point charges
• It is valid over distance as small as of the order of 10^-15 m to several kilometers.
• It depends on the nature of intervening medium.

Dielectric constant : The dielectric constant or relative permittivity of a medium is the ratio of abslute permittivity of the medium to the absolute permittivity of free space.
Dielectric constant depends on the temperature of the medium.
Dielectric constant of water is about 80, so force between two given charges a given distance apart placed in water is 80 times less than when placed in vacuum or air.

Unit of charge:

SI unit of charge is coulomb (c): One coulomb is such a point charge which when placed in vacuum are metre apart from another similar point charge of equal strength repel one another with a force of 9 × 10⁹ N

CGS unit of charge is electrostatic unit (esu): One electrostatic unit of charge is such a point charge which when placed in vacuum one centimetre apart from another similar point charge of equal strength repel one another with a force of one dyne.

1 coulomb = 3 × 10⁹ esu charge

Electric potential: Electric potential at a point in the electric field is defined as the work done per unit charge in moving a unit positive test charge from infinity to that point against the electrostatic force of the field irrespective of the path followed.

Unit of electric potential :

SI unit : Volt (c) : The potential at point is one volt if one joule of work is done in moving one coulomb of charge from infinity to that point in an electric field.

CGS unit: Siat Volt : Potential at a point is one stat volt if one erg of work is done in moving one stat coulomb of charge from infinity to that point in the electric field.

1 stat volt = 300 volt

Potential difference between two points: Potential difference between any two points in an electric field is the work done per unit charge is moving a unit positve charge from one point to the other against the electrostatic force of the field irrespective of the path followed.

Unit of potential difference :

• SI unit : Volt
• CGS unit : Stat volt

Ohm’s Law (1826) : The temperature and other physical condition remaining constant, the current flowing through a conductor is directly proportional to the potential difference across the ends of the conductor.

V ∝ I or, V = RI

Graphical representation of Ohm’s Law: The variation of V and I for two conductors A and B is shown in fig(a). These are straight line having constant

slope = \(\frac{V}{I}\) = R

So, higher the slope means the higher resistance of the conductor. Thus we find B has higher resistance R than that of A.

In the same way fig(b) shows variation of I and V for these two conductors A and B.

Here slope \(\frac{1}{V}\) = \(\frac{1}{R}\), shows that larger the slope, smaller is the value of the resistance of the conductor.

Ohmic conductors : Ohm’s law is found to be valid for a wide range of current and potential in all the metallic conductors and also in some other materials. These conductors are called ohmic conductors.

Non-Ohmic conductors: When the Ohm’s law is found not to be applied for conduction of electricity through vacuum tube, semiconductors and also to electric discharge through gases at low pressure. These are called non-ohmic conductors.

Resistance : The resistance of a conductor is the opposition offered by it to the flow of electric current through it

R = \(\frac{V}{I}\)

(R = resistance of a conductor
V = Potential difference
I = current flowing through a conductor)

Resistivity or specific resistance : The resistivity or specific resistance of the material of a conductor is numerically equal to the resistance between the opposite faces of a unit cube when current flows normally to the faces.

• Unit of Resistivity :
• Ohm-centimetre (Ω-cm)
• Ohm-metre (Ω-m)

Resistance of a given conductor depends on the following factors:

• Length of the conductor: The resistance of a given conductor is directly proportional to its length. R ∝ l
• Area of the conductor: The resistance of a given conductor is inversely proportional to its area of cross-section :
• [R ∝ \(\frac{1}{A}\)]
• Nature of the meterial and temperature of the material of the conductor: We have resistivity,

r = \(\frac{R A}{l}\)

Difference between Resistance and Resistivity :

Resistance	Resistivity
i. Resistance of a conductor depends on the nature of the material of a conductor and also on its dimensions.	i. Resistivity of a conductor depends on the nature of the material of a conductor but independent of its dimension.
ii. Resistance is the property of a body.	ii. Resistivity is the property of the material of the body.
iii. Ohm-meter is an instrument for measuring resistance.	iii. Oi.m-meter is the unit of resistivity.
iv. Dimensional formula of resistance (R) = [ML2T-3A-2]	iv. Dimensional formula of resistivity (ρ) [ρ] =[ML3T-3A-2]

Combination resistance: In different electri al circuit more than one resistance are connected together. This is known as resistance.

Series combination : A number of resistances are said to be in series combination if they are connected one after the other in such a way that the same current flows through all the resistance when same potential difference is applied across the combination.

r = r₁ + r₂ + r₃

Parallel combination : A number of resistance are said to be connected in parallel if one end of all the resistances are joined together and the other ends joined to another point such that the potential difference across each resistance is equal to the applied pr ential difference across the combination.

Internal resistance of a cell : Internal resistance offered by the electrolyte and electrodes of a cell when electric current flows through the cell.

Joule’s Laws :

First Law : The amount of heat produced in a conductor in a given interval of time is proportional to the square of the current passed
H ∝ P² (when R and t are kept constant)

Second Law : The amount of heat produced by a given current in a given time is proportional of the resistance of the conductor.

H ∝ R (when I and t are kept constant)

Third Law : The amount of heat produced in a given conductor by a given current is proportional to the time for which the current passes.
H ∝ t (when I and R are kept constant)
Combining the three laws, we have
H ∝ I² R t
(when I, R and t vary)
or, H = \(\frac{I^2 R t}{J}\)
(J = mechanical equivalent of heat
= 4.2 joul/calorie.)
If I be in ampere, R in Ohm, t in second and H in calorie, then
H = \(\frac{I^2 R t}{4 \cdot 2}\)
or, H = 0.24 I² R t calorie

Fuse : For the safety of the electrical gadgets one thin wire made of an alloy of lead (75 %) and tin (25 %) and which has high resistance and low melting is kept in an insulator box of china clay. The thin coil is called fuse wire. The wire is kept in series with the main circuit of the household electrical appliances.

Electric iron: In this a thin but long wire of nichrome is kept coiled and sandwitched betwen two sheets of mica. This is called the heating element of the iron. The element is kept inside two iron plates and the heating element is kept insulated from the external body of the iron. On passing current through the element it gets heated and the iron in turn becomes hot.

Electric heater: In this, a thin and long wire of nichrome, is kept coiled in the spiral grooves of a porcelain block. This block is kept in metallic case and there is arrangement for making electrical connection with two ends of the coil.

Electric bulb : A thin but long coiled coil (filament) of tungsten wire is introduced in evacualed glass blub. Sometimes the bulb is filed with some inert gases. Electric contact to the filament is made by two comparatively thick wires. The resistance of the filament wire is such that it may glow being strongly heated by the electric current.

If a bulb be marked as ‘220 V-60 W’ then we mean that the lamp should be used at a potential difference of 220 Volts and on doing so it will glow fully and electrical energy will be spent at the rate of 60 joules per second or a power of 60 W} will be required.

It should be remembered that although same current through the filament of the bulb and the line wires, the resistance of the filament wire being much larges, the heat (I² R) produced in it is much larger and hence glows brightly. It may be further noted that they resistance of the bulb marked 200 V-100 W is less than another marked 200 V-60 W. As a result more current passes through the coils of the former bulb and more heat (I² R) is produced in it thus glows more brightly.

Units of electrical power and energy :

Watt : The SI unit of electrical power is watt. A watt is the power expended when one ampere of current flows under a potential difference of one volt.

so placed that the current carrying wire lies between the palm and the needle and the palm always facing the wire and the fingers pointing in the direction of the current, then the outstretched thumb will give the direction of deflection of the north pole of the needle.

Magnetic field: The magnetic field at any point in the field is numerically equal to the force experienced by a unit charge moving with a unit velocity perpendicular to the direction of the magnetic field at that point.

Fleming’s left hand rule : If the first finger, the middle finger and the thumb of the left hand be stretched mutually perpendicular to each other in such a way that the first-finger points in the direction of the magnetic field and the middle-finger points in the direction of electric current, then the thumb gives the direction of the force acting on the conductor.

Ampere’s circuital Law : It states that the line integral of magnetic field around any closed path in vacuum is equal to absolute permeability times the total current enclosed by the path.

Moving coll galvanometer : A moving coil galvanometer is an instrument for detection and measurement of small electric current.

Ammeter : An ammeter is a low resistance galvanometer, which is used to measure current in a circuit.

Voltmeter : A voltmeter is a high resistance galvanometer used to measure the potential difference between two points of an electrical circuit.

Diamagnetic substances : Diamagnetic substances are those in which the individual atoms or molecules or ions do not possess any net magnetic moment of their own.

Paramagnetic substances: Paramagnetic substances are those in which each individual atom or molecule or ion has a net non-zero magnetic moment of its own and placing such a material in an external magnetic field, it tries to align the individual dipole moments in the direction of the magnetic field.

Barlow’s wheel: Action of the magnet on a current and how rotational motion can be produced due to this effect can be shown by the experiment on Barlow’s wheel.

Electric motor: The device or machine which converts the electrical energy into mechanical energy is known as Electric Motor.

Solenoid : If many turns an insulated wire would around a cylinder the resulting coil is known as solenoid.

An ammeter has a low resistance and as it is connected in series in a circuit, so it reads slightly less than the actual current.

While giving reading a small current always passes through a voltmeter, so it cannot be used for determining the emf of a cell. For which a potentiometer is used, where at balanced condition no current passes through the cell.

The resistance of an ideal ammeter is zero.
The resistance of an ideal voltmeter is infinity.
The ammeter is a low resistance instrument and connected in series in an electrical circuit.

The voltmeter is a high resistance instrument and connected in parallel across the circuit.

Ferromagnetic substances: Ferromagnetic substances are those in which each individual atom or molecule or ion has a non-zero magnetic moment, same as in a paramagnetic substance.

Magnetic flux: The magnetic flux through any surface held in a magnetic field is measured by the total number of magnetic lines of force crossing the surface.

Faradav’s laws of electromagnetic induction :

First Law : Whenever there is a change in the magnetic flux linked with a coil, an emf is induced in it and its emf lasts as long as the change in the magnetic flux continues.

Second Law : The magnitude of the emf induced in the coil is proportional to the rate of change of magnetic flux linked with the coil.

Lenz’s Law : The induced current will be in such a direction that it opposes the cause which produces it.

Faraday’s law as modified by Lenz’s law: The emf induced in a coil is given by the negative of the rate of change of magnetic flux linking with its turns.

Fleming’s right hand rule: If the first finger, central finger and thumb of the right hand be stretched in the mutually perpendicular directions such that the first finger points along the direction of the field and thumb be along the direction of motion of the conductor, then the central finger would give the direction of induced current. It is also called dynamo rule.

Eddy currents : Eddy currents, first discovered by Foucault in the year 1895, are the currents induced in the body of a conductor when the amount of magnetic flux linked with the conductor changes. After the name of its discoverer, it is also called Foucault current.

Alternating current : An electric current, magnitude of which changes with time and direction reverses periodically is called alternating current (a.c.).

I = I₀ sin ω t or I = I₀ cos ω t

where I is the instantaneous value of current i.e. the magnitude of the current at any instant of time t, I₀ is the peak value or maximum value or amplidue of a.c. and ω is the angular frequency of a.c.

The terms used for alternating current hold equally for alternating e.m.f and may be represented as

E = E₀ sin ω t or E = E₀ cos ω t

where E and E₀ are the instantaneous and maximum or peak value of the alternating emf respectively.

Advantages and disadvantages of a c. over d.c

Advantages of a.c. over d.c. :

• Generation, transmission, distribution of a.c. is more economical and convenient.
• A.C. can be controlled more effectively and easily with very little loss of power by using inductors.
• A.C. can be transmitted with very little loss of power using transformer.
• A.C. can be easily converted in d.c. by using rectifiers.
• Using transformers a.c. voltages can be stepped up or stepped down to any desired value.

Disadvantages of a.c. over d.c.

• A.C is more dangerous than d.c.
• A.C. cannot be used in electrolysis.
• Calibrations of A.C. meters for small measurements are difficult as the markings are not equidistant.
• Conduction of a.c. through metal wires suffer skin effect.

A.C. generator or Dynamo: An a.c. generator or dynamo is an device used to convert mechanical energy into electrical energy.
An a.c. generator works on the principle of electromagnetic induction i.e. when a coil is rotated in uniform magnetic field, an emf is induced in the coil.

The main components of a.c. generator are:

• Armature : It is a coil having a large number of turns of insulated copper wire wound on a soft iron core.
• Field magnet : A strong permanent magnet with cylindrical pole pieces is used as a field magnet. The uniform magnetic field produced by it is perpendicular to the axis of rotation of the coil.
• Slip rings : Two terminals of the armature coil are connected to two slip rings made of brass. These rings rotate with the coil.
• Brushes : There are two carbon brushes touching two slip rings and remain fixed while slip rings rotate along with the coil. The brushes are connected to the output through load.

Following Faraday’s laws of electromagnetic induction, the induced emf produced in the coil given by

E = E₀ sin ω t

D.C. generator or Dynamo: A d.c. generator is similar, in many ways, to an a.c generator. In the internal circuit of a d.c. generator, current is produced in the same way as in the internal circuit of an a.c. generator but the current in the external circuit of a d.c. generator, is unlike that of an a.c. generator, direct and not alternating. The alternating current is converted into direct current by a commutator which is nothing but a pair of semicircular ring. These are called split rings.

Barlow’s wheel : The action of magnet on current and there by rotation of the conductor itself, is demonstrated by Barlow’s wheel.

Factors governing the speed of Rotation :

• Rotational speed increases with current and vice versa.
• Rotational speed increases with intensity of magnetic field and vice versa.
• If alternating current (ac) is used instead of direct current (dc), the wheel wire try to reverse it’s direction with the change in direction of current resulting no rotation.

Factors governing the direcion of Rotation :

The direction of rotation will reverse if direction of current is reverse keeping direction of magnetic field intact.
The direction of rotation will reverse if direction of magnetic field is reversed keeping direction of current intact.
The direction of rotation will remain unchanged if both direction of magnetic field and direction of current are reversed.

Electrical Switch: An electrical switch in any device used to interrupt the flow of electrons in a circuit.

Types of Switch :

Toggle switch : Toggle switches are actuated by a lever angled in one of two or more positions. The common light switch used in household wiring is an example of toggle switch.

Push button switch : Push button switches are two-position devices actuated with a button that is pressed and released most push button switches have an internal spring mechanism returning the button to its ‘out’ or ‘unpressed’ position for momentary operation.

Selector switch : Selector switches are actuated with a rotary knob or lever of some sort to select one of two or more positions.

Joystick swich : A joystick to actuated by a lever free to move in more than one axis of motion.

Lever actuator limit switch : These limit switches closely resemble rugged toggle or selector hand switches fitted with a lever pushed by the machine part.

Proximity switch : Proximity switch sense the approach of a metallic machine part either by a magnetic or high-frequency.

Speed switch : These switches sense the rotary speed of a shaft either by a centrifugal weight mechanism mounted on the shaft or by some kind of non-contact detection of shaft motion such as optically or magnetic.

Pressure switch : Gas or liquid

pressure can be used to actuate a switch mechanism if that pressure is applied to a piston, diaphram, or bellows with converts pressure to mechanical force.

Socket : Socket may refer to

In machanics

• Socket wrench : A type of wrench that uses separate, removable sockets to fit different sizes of nuts and bolts.
• Socket head screw: A screw (or bolt) with a cylindrical head containing a socket into which the hexagonal ends of an Allen wrench will fit.
• Socket termination : A termination used at the ends of wire rope.

In biology :

• Eye socket: A region in the skull where the eyes are positioned.
• Tooth socket: A cavity cantaining a tooth, in those bones that bear teeth.
• Dry socket: A painful opening as a result of the blood not clotting after a tooth is pulled.0
• Ball and socket joinf.

In computer networking :

• Networking socket : an end-point in a communication across a network or the internet.
• Unix domain socket : an end point in local inter-process communication.

Electrical and electronic connectors :

• AC power plugs and sockets : Electrical devices used to connect to a power source onto which another device can be plugged or screwd in.
• Antenna socket, a female antenna connector for television cable.
• CPU socket : The connector on a computer’s motherboard for the CPU.
• Jack (connector) : One of several types of electronic connectors.
• Lamp socket : A connector into which a light bulb screws.

Live wire, neutral wire: An electric current is a flow of electric charge. Most mains powered appliances need three wires to work safely. They are live, neutral and earth.

Only two of the wire are used when the appliance works properly. These are the live (brown) and the neutral (blue) wires. The live wire carries current to the appliance at a high voltage. The neutral wire completes the circuit and carries current away from the appliance. The third wire called the earth wire (green/yellow) is a sefely wire and connects the metal case of the appliance to the earth. This stops a fault making the case of the appliance live.

Earthing: If a fault occurs where the live wire connects to the case the earth wire allows a large current to flow through the live and earth wires. This overheats the fuse which melts and breaks the circuit appliance such as hairdryers are said to be ‘double insulated’ and there’s no need for an earth wire because the case is made of a non conducting plastic. If a faulty live wire touches the inside of the plastic case there’s little risk as the case is an insulator.

Main switch (Isolator): The 100 A rated main switch is a switch disconnector which can be used as an Isolator, and can be used for residential and light commercial applications.

The operating switch can be locked in the ON or OFF position, using a device lock. The main switch has a positive contact status indicator, i.e. when green window is visible this indicates that there is a 4 mm contact gap.

Diagram showing Domestic wiring : Generally the live wire is red, neutral wire is black and earth wire is green in domestic electrical wiring. All appliances are kept in parallel through a switch so as to ensure 220 volt across all appliances. Each appliance should be provided with separate switch.

Detailed explanations in West Bengal Board Class 10 Physical Science Book Solutions Chapter 8.2 Ionic and Covalent Bondings offer valuable context and analysis.

WBBSE Class 10 Physical Science Chapter 8.2 Question Answer – Ionic and Covalent Bonding

Very Short Answer Type Questions :

Question 1.
What is a chemical bond?
Answer:
Chemical bond is a strong force of attraction that holds together atoms in a molecule or crystal.

Question 2.
What is the electronic configuration of noble gases in their valence shell ?
Answer:
Noble gases (except helium) have eight electrons in their valence shell i.e. they have ns², np⁶ configuration.

Question 3.
Why noble gases are inert?
Answer:
The inert nature of noble gases is due to their stable electronic configuration.

Question 4.
How does electrovalency occur?
Answer:
Electrovalency occurs due to shifting of electron.

Question 5.
What is the common reason behind the phenomena of electron release and electron sharing by elements?
Answer:
This is due to the tendency of elements to attain stable state of their nearest elements in periodic table.

Question 6.
What type of valency would be exhibited when an element combines with sodium ?
Answer:
Electrovalency.

Question 7.
Why are electrovalent compounds generally solid ?
Answer:
Electrovalent compounds are generally solid due to strong attractive electrostatic force between ions of opposite charges.

Question 8.
How is the valency of an element in an electrovalent compound measured ?
Answer:
The valency of an element in an electrovalent compound is measured by the number of electrons gained or lost by one atom of the element.

Question 9.
Name a covalent compound.
Answer:
Water (H₂O) is covalent compound.

Question 10.
Name an electrovalent compound.
Answer:
Sodium chloride (NaCl) is an electrovalent compound.

Question 11.
Name the type of valency where electrons are shared ?
Answer:
Electrons are shared in covalency.

Question 12.
Which class of substance is a common component of all electrovalent compounds ?
Answer:
A metal is common component of all electrovalent compounds.

Question 13.
State one characteristic of covalent compounds.
Answer:
Covalent compounds do not produce ions in solution or in fused states, so these are non-electrolytes.

Question 14.
What is the valency of carbon in CH₄ compound?
Answer:
The valency of carbon is 4 in CH₄ compound.

Question 15.
What is the nature of ionic bond ?
Answer:
Tonic bond is non-directional in nature.

Question 16.
SnCl₄ is a poor conductor of electricity. Why ?
Answer:
SnCl₄ being a covalent compound does not ionise and hence is a poor coductor of electricity.

Question 17.
What is the C – C bond length in saturated compounds ?
Answer:
The C-C bond length in saturated compounds is 1.54A°

Question 18.
What is the structure of ammonia ?
Answer:
The structure of ammonia is pyramidal.

Question 19.
What is the nature of bond formed between Cs and F ?
Answer:
The nature of bond formed between Cs and F is ionic.

Question 20.
Name of compound which contains both ionic and covalent bond.
Answer:
Potassium cyanide (KCN)

Question 21.
How many electrons take in forming bonds in N₂ ?
Answer:
The total number of electrons that take part in forming bonds in N₂ is 6.

Question 22.
Name the element which has highest electronegativity.
Answer:
‘F’ has highest electronegativity (4.0).

Question 23.
Consider two elements with atomic no. 37 and 53. What will be the bond between their atoms?
Answer:
Covalent.

Question 24.
What will be the shape of ethane?
Answer:
The shape of ethane is tetrahedral.

Question 25.
What is the type of bonding in ferric chloride ?
Answer:
The lype of bonding in ferric chloride is covalent.

Question 26.
Name an element which has zero electronegativity?
Answer:
Helium has zero electronegativity.

Question 27.
How many lone pair(s) is/are present XeOF₄ ?
Answer:
1 (one).

Question 28.
On which does lattice energy of an ionic compound depend ?
Answer:
Lattice energy of an ionic compound depends upon charge and size of the ion.

Question 29.
Give the name of one electrovalent substance which is used in everyday life.
Answer:
Sodium chloride (NaCl)

Question 30.
Give the name of one covalent substance which is used in everyday life.
Answer:
Water (H₂O).

Question 31.
Which one of NaCl and C₆ H₁₂ O₆ will have higher melting point?
Answer:
NaCl.

Question 32.
What types of bonds are expected between hydrogen atom and chlorine atom is HCI(g) molecule ?
Answer:
Covalent.

Question 33.
Atomic numbers of two elements A and B are 20 and 17 respectively. What would be the nature of the bond (covalent or electrovalent) between them if they combine chemically among themselves ?
Answer:
Electrovalent.

Question 34.
How many electrons are there in the outermost shell of the atom of the element carbon?
Answer:
four (4).

Question 35.
Between MgCl₂ and CHCl₃ which one is electrovalent in nature?
Answer:
MgCl₂.

Question 36.
What do you mean by valence shell ?
Answer:
The outermost shell of an atom is known as valence shell.

Question 37.
What is the nearest inert element of chlorine atom ?
Answer:
The nearest inert element of chlorine atom is argen (Ar).

Question 38.
What is the valency present in NaH ?
Answer:
Electrovalency is present in NaH.

Question 39.
What is the nearest inert element of carbon ?
Answer:
The nerest inert element of carbon is neon (Ne).

Question 40.
What are the types of Covalent bond ?
Answer:
Covalent bonds are of three types.
They are : (i) Covalent single bond (ii) covalent double bond (iii) coval at triple bond

Question 41.
What kind of bonding is present in substances which are nonelectrolytes?
Answer:
Covalent Bonding

Question 42.
The lonic crystals are always brittle-why?
Answer:
If mechanical pressure is applied to an ionic crystal then ions of similar charges may be forced to get closer to each other. By doing so, the electrostatic repulsion can be enough to split or disorient the lattice structure completely. This imparts brittleness to the structure.

Question 43.
Who proposed the electron dot structures to describe the bonding in simple covalent compounds ?
Answer:
Lewis proposed the electron dot structures to describe the bonding in simple covalent compounds.

Question 44.
Which bond has directional property?
Answer:
Covalent bonds have directional property.

Question 45.
Ionic bonds are non-directional in nature why?
Answer:
The attractive forces between ions in ionic compounds expend equally in all possible directions. It acts neither in a specific direction nor in confined to two particular ions. So, ionic bonds are non-directional in nature.

Question 46.
Give example of a covalent compound which can conduct electricity in aqueous solution.
Answer:
Hydrogen chloride ( HCl), though a covalent compound, undergoes complete ionization in water and conducts electricity in its aqueous solution.

Question 47.
Write the name of an ionic compound in which both the atoms of the component elements do not have octet.
Answer:
Lithium hydride (LiH) is the ionic compound in which both Li and H have duplet and not octet.

Question 48.
Sulphur is soluble in carbon disulphide but insoluble in waterexplain why?
Answer:
Carbon disulphide is a non-polar solvent and water is a polar solvent. Sulphur, being a covalent element molecule, is therefore soluble in non-polar carbon disulphide but not in water.

Short Answer Type Questions :

Question 1.
What are the causes of chemical combination ?
Answer:
Cause of chemical combination :
(i) Tendency to acquire noble gas configuration.
(ii) Tendency to acquire minimum energy.

Question 2.
What are the common types of bonds ?
Answer:
Depending upon the mode of acquiring nerest noble gas configuration, there are three common types of bonds :
(i) Ionic or Electrovalent bond, (ii) Covalent bond and (iii) Co-ordinate or Dative bond.

Question 3.
What are the main types of physical bonds ?
Answer:
The main types of physical bonds are : (i) Hydrogen bond, (ii) Metallic bond, (iii) Van der Waal’s interactions

Question 4.
What is the electronic theory of bonding ?
Answer:
Electronic theory of bonding : Atoms combine by transfer of electrons (ionic bonding) or by sharing of electrons (covalent bonding).

Question 5.
What is lonic bonding ?
Answer:
Ionic bonding : The electrostatic force of attraction which holds the oppositely charged ions together is called ionic bond or electrovalent bond and the compounds which are formed by the transference of electrons from one atom to other are known as ionic or electrovalent compounds. The number of electrons which an atom loses or gains while forming an ionic bond is known as electrovalency.

Question 6.
What are the conditions necessary for the formation of lonic bond ?
Answer:
Conditions necessary for the formation of Ionic bond :

1. Formation of cation from a neutral atom having low ionisation energy.
2. Formation of an anion from a neutral atom with high value of electron affinity.
3. Formation of crystal lattice from oppositely charged ions involving large release of energy.

Question 7.
What is Lattice energy ?
Answer:
Lattice energy : Lattice energy of an ionic solid is the amount of energy released when required number of cations and anions combine to form one mole of an ionic solid.

Question 8.
What are the factors by which Lattice energy depends ?
Answer:
Lattice energy depends upon the following factors :

1. Magnitude of charge of ions : It increases with increase in charge on cation, anion or both.
2. Size of cation : For a common anion, the lattice energy decreases with increase in size.
3. Size of anion : For a common cation, the lattice energy decreases, with increase size of anion.

Question 9.
What are the characteristics of ionic compounds ?
Answer:
Characteristics of ionic compounds :

1. All ionic compounds are usually crystalline solids and are composed of ions even in the solid state.
2. Ionic solid have high melting points and boiling points due to the presence of strong attractive forces between the oppositely charged ions.
3. Ionic compounds have low volatility high density and high stabiliy.
4. lonic compounds are highly soluble in polar solvents (such as water) having high dielectric constant (80) but insoluble in organic solvents (such as benzene, alcohol. ether etc.)

Question 10.
What type of valency is shown when sodium combines chemically with chlorine?
Draw the relevant electron dot diagram.
Answer:
Electrovalency is shown when sodium combine chemically with chlorine.
Electron dot diagram :

Question 11.
State the common reason behind the phenomena of electron release or electron capture by atoms to form ions.
Answer:
Explanation : An element goes into chemical bondage with another element since it tends to attain the stable state of its nearest inert element in the periodic table. To fulfill this, an atom either gains or loses electrons to possess 8 electrons or 2 electrons (for hydrogen atoms) in its outermost orbit. As a result of losing electrons, atoms are transformed to positive ions and on gaining electrons atoms transform to negative ions.

Question 12.
What type of valency is shown in Li₂O ? Draw the relevant electron dot diagram.
Answer:
Li₂ O Shows electrovalency.
Electron dot diagram :

Question 13.
What type of bonding is present in CaO ?
Answer:
Ionic bonding is present in CaO
Electron dot diagram :

Question 14.
What type of bonding is present in MgCl₂ ?
Answer:
Ionic bonding is present in MgCl₂
Electron dot diagram :

Question 15.
What type of valency is shown in Al₂ O₃ ?
Answer:
Flectron dot diagram :

Question 16.
What is covalent bond?
Answer:
Covalent bond (G.N. Lewis, 1916): A covalent bond is formed by the mutual sharing of electrons between the atoms, both of which are short electrons. The compound so formed is called covalent compounds. The member of electrons contributed by an atom for sharing is known as its covalency. Depending upon the number of electrons shared between two atoms being one, two or three, we have single covalent bond (: or = ), double covalent bond (:: or = ) and triple covalent bond ( :: or ≡ ).

Question 17.
What is octet rule ?
Answer:
Octet rule It states that atoms react because they have a tendency to complete their octet (or duplet) i.e. to have eight electrons in the valence shell (or two electrons if only one shell is present). They can do so by losing, gaining or sharing electrons.

Question 18.
What are the exceptions of octet rule ?
Answer:
Exceptions of octet rule There are many atoms which do not obey the octet rule and may contain six (as in BF₃ ), ten (as in PF₃ ) electrons.

Question 19.
What are the characteristics of covalent compounds?
Answer:
Characteristics of covalent compounds :

1. Covalent compounds exist in solid, liquid and gaseous state.
2. These compounds have low melting and boiling points.
3. These (except graphite) are bad conductors and react slowly.
4. These are soluble in non-polar solvents such as benzene, acetone etc., but are insoluble in polar solvents such as water.
5. Due to the directional nature of covalent bonds, these compounds show stereoisomerism.

Question 20.
What type of bonding is present in nitrogen molecule ?
Answer:
Covalent bonds are present in nitrogen molecule :
Diagram :

Question 20.
What type of bonding is present in oxygen molecule ?
Answer:
Covalent bonds are present in oxygen molecule.
Diagram :

Question 21.
What type of bonding is present in hydrogen molecule ?
Answer:
Covalent bond is present in hydrogen molecule.
Diagram :

Question 22.
How HCl(g) molecule is formed ?
Answer:
Covalent bond is present in HCl(g) molecule.
Diagram :

Question 23.
How water molecule is formed ?
Answer:
There are two covalent bonds in water molecule.
Diagram :

Question 24.
How methane molecule is formed?
Answer:
These are four covalent bonds in methane molecule.
Diagram :

Question 25.
How ammonia molecule is formed ?
Answer:
These are three covalent bonds in ammonia molecule.
Diagram :

Question 26.
How carbon dioxide molecule is formed ?
Answer:
These are four covalent bonds present in carbon dioxide molecule.
Diagram :

Question 27.
Why does the tendency of sharing electrons grows in many nonmetallic atoms during formation of covalent compounds ?
Answer:
Explanation : During formation of covalent compounds of non-metallic atoms, each participant involved in the process tends to attain duplet or octet stable state. To attain such stable state they share electrons.

Question 28.
Writ town the electronic configuration of a chlorine atom, a chlorine ion.
Answer:
Electronic configuration of chlorine atom is : 2, 8, 7.
Electronic configuration of a chlorine ion is : 2, 8, 8.

Question 29.
What is co-ordinate bond or dative bond ?
Answer:
Co-ordinate bond : It is a special type of covalent bonding where the shared pair of electrons is supplied only by one of the atoms forming the bond. The atom which supplies the shared pair of electrons is called donar while the atom which only uses the shared pair of electrons is called acceptor. e.g. Ammonium ion (\(\mathrm{NH}_4⁺}\))

Question 30.
SnCl₄ is a poor conductor of electricity. Why ?
Answer:
Explanation SnCl₄ being a covalent compound does not ionise and hence, is a poor conductor of electricity.

Question 31.
Covalency possesses directional properties but electrovalency has no such characteristics. Why ?
Answer:
Explanation Shared electron pairs of covalent bonds are localised between two atoms. Hence covalent bonds have directional character on the other hand oppositely changed ions in electrovalent compounds are held together by electrostatic forces of attraction which in non-directional in nature.

Question 32.
HCI gas is a covalent compound but its water solution conducts electricity. Why ?
Answer:
Explanation Electro-negativity of Cl and H are 3 and 2.1 respectively. The difference in the electro-negativities of Cl and H being 0.9, the bond in HCl is a polar covalent bond. When gaseous HCl is dissolved in water, then due to high dielectric constant of water (80), it breaks apart, the positive and negative ends of the dipole in HCl molecule giving H₃ O⁺ and Cl^– ions which conduct electricity.
HCl(g) + H₂O(l) → H₃O⁺ (aq) + Cl^– (aq)

Question 33.
Amongst LiF and Lil which has more covalent character and why ?
Answer:
Explanation : Lil has more covalent character because Li⁺cation will be able to polarize the bigger I^–more than the smaller F^–ion. Greater polarisation in Lil leads to more covalent character.

Question 34.
Water is generally a good solvent for lonic compounds. Why ?
Answer:
Explanation : Dielectric constant of water being high (80), the electrostatic force of attraction between oppositely charged ions gets reduced to (1/80) of original force in air. Hence, ions of an electrovalent compound get separated which then solvated by waters.

Broad Answer Type Questions: 

Question 1.
What is the difference between ionic compounds and covalent compounds ?
Answer:
Difference between ionic and covalent compounds :

Ionic Compounds	Covalent Compounds
i. These are formed by the transfer of one or more electrons from one atom to another.	i. These are formed by the sharing of one or more electrons between the bonded atoms.
ii. These consist of ions.	ii. These consist of individual molecules.
iii. These are soluble in water but insoluble in organic solvents.	iii. These are insoluble in water but soluble in organic solvents.
iv. These are hard solids with high melting and boiling points.	iv. These exist as gases, liquids or soft solids with low melting and boiling points.
v. These undergo ionic reactions which are very fast.	v. These undergo molecular reactions which are very slow.
vi. These conduct electricity in fused as well as aqueous solutions.	vi. These do not conduct electricity.
vii. These do not show isomerism.	vii. These show isomerism.

Question 2.
The atomic number of the element A is 20 and that of another element B is 17. Write down their electronic configurations. Will they produce an electrovalent compound or a covalent compound ? What will be their valencies in that case?
Answer:
Electronic configuration of A is : 2,8,8,2.
Electronic configuration of B is : 2,8,7.
They will produce and electrovalent compound.
Explanation . An atom A will give up two (2) valence electrons, each of two atoms of B will capture one electron. In the process atoms of A and B attain stable octet state and atoms of A will be positive ions and those of B will be negative ions. A and B thus form electrovalent compound.
As, an atom of A loses two electrons. So A has valency 2 (two) and since each atom of B captures one electron, the valency of B will be one (1).

Question 3.
Write down electronic arrangement of the element \({ }_{17}^{35} \mathrm{X}\)
1. what is the valency of the element?
2. will the element form anion or cation?
3. what type of valency will be exhibited when the element combines with sodium?
Answer:
The electronic configuration of the element X is : 2,8,7,

1. As an atom of the element tends of capture or share one electron to attain stable of octet, its valency is 1.
2. It will form anion by capturing electron.
3. The element will exhibit electro-valency when it combines with sodium since sodium is a metal, and atom of which tends to release one electron.

Well structured WBBSE Class 10 Physical Science MCQ Questions Chapter 8.1 Periodic Table and Periodicity of the Properties of Elements can serve as a valuable review tool before exams.

Periodic Table and Periodicity of the Properties of Elements Class 10 WBBSE MCQ Questions

Multiple Choice Questions :

Question 1. The basis of modern periodtc table is :
(A) atomic volume
(B) atomic number
(C) atomic weights
(D) atomic size
Answer:
(A) atomic volume.

Question 2.
Which of the following has the maximum value of electron affinity?
(A) F
(B) Cl
(C) Br
(D) I
Answer:
(B) Cl

Question 3.
The elements of group IIA and IIA are known as :
(A) s-block elements
(B) p-block elements
(C) typical elements
(D) transition elements
Answer:
(A) s-block elements

Question 3.
Characteristic of transition elements is incomplete :
(A) d-orbitals
(B) f-orbitals
(C) p-orbitals
(D) s-orbitals
Answer:
(A) d-orbitals

Question 4.
The electron affinity of inert gases is likely to be :
(A) high
(B) negative
(C) positive
(D) zero
Answer:
(D) zero

Question 5.
The element with the highest first ionization potential is :
(A) boron
(B) carbon
(C) nitrogen
(D) oxygen
Answer:
(C) nitrogen

Question 6.
In second period, if we move from Li to F, there is regular decrease in :
(A) atomic mass
(B) atomic radius
(C) electronegativity
(D) ionization potential
Answer:
(B) atomic radius

Question 7.
Compared to the first ionisation potential of an atom, the second is:
(A) the same
(B) greater
(C) smaller
(D) negligible
Answer:
(B) greater

Question 8.
Which has the largest first ionization energy ?
(A) Li
(B) Na
(C) K
(D) Rb
Answer:
(A) Li

Question 9.
The outermost electronic configuration of the most electronegative element is :
(A) ns² np³
(B) ns² np⁴
(C) ns² np⁵
(D) ns² np⁶
Answer:
(C) ns² np³

Question 10.
Which one of the following has the largest size ?
(A) Br^–
(B) I^–
(C) I
(D) \(I^{\oplus}\)
Answer:
(B) I

Question 11.
Which one of the following is the smallest in size ?
(A) N^3-
(B) O^2-
(C) F^–
(D) Na⁺
Answer:
(D) Na

Question 12.
All the elements in a group in the periodic table have the same:
(A) atomic weight
(B) atomic number
(C) number of electrons available for bonding
(D) atomic mass
Answer:
(C) number of electrons available for bonding.

Question 13.
‘The law of triads’ is applicable to the following :
(A) Cl, Br, I
(B) H, O, N
(C) Na, Ne, Ca
(D) None of the above
Answer:
(A) Cl, Br, I

Question 14.
The element in the third group and third of periodic table is :
(A) B
(B) Na
(C) Al
(D) Mg
Answer:
(C) Al

Question 15.
The law of octaves applies to :
(A) B, C, N
(B) As, K, Ca
(C) Be, Mg, Ca
(D) None of the above
Answer:
(C) Be, Mg, Ca

Question 16.
In which group of the periodic table will the element with atomic number z=17 occur ?
(A) IA
(B) IIIB
(C) VIIB
(D) VIB
Answer:
(C) VIIB

Question 17.
Pnicogens are the elements belonging to the :
(A) 12 group
(B) 13 group
(C) 15 group
(D) 16 group
Answer:
(C) 15 group

Question 18.
5f-subshell is successively filled up in :
(A) actinoids
(B) lanthanoids
(C) trypical metals
(D) normal metal
Answer:
(A) actinoids

Question 19.
In the long form periodic table, the block containing non-metals is:
(A) s
(B) p
(C) d
(D) f
Answer:
(B) p

Question 20.
Variable valency is shown by :
(A) typical elements
(B) normal elements
(C) transition elements
(D) none of the above
Answer:
(C) transition eleme is

Question 21.
Which of the following form coloured salts ?
(A) non-metals
(B) metals
(C) p-block elements
(D) transition elements
Answer:
(D) transition elements

Question 22.
Which of the following does not reflect the periodicity of elements :
(A) Bonding behaviour
(B) Electronegativity
(C) Ionisation-potential
(D) Neutron/proton ratio
Answer:
(D) Neutron prolon ratio

Question 23.
Zero group wasjntroduced by
(A) Lother Meyer
(B) Mendeleev
(C) Ramsay
(D) Locker
Answer:
(C) Ramsay

Question 24.
The telluric helix was given by :
(A) Newlands
(B) Lother Meyer
(C) Mendeleev
(D) De Chancourtois
Answer:
(D) De Chancourtois

Question 25.
Lithium shows diagonal relationship with :
(A) Ne
(B) Mg
(C) Be
(D) Ce
Answer:
(B) Mg.

Question 26.
The number of elements discovered till date is :
(A) 63
(B) 109
(C) 60
(D) 118
Answer:
(D) 118

Question 27.
At the time of publication of Mendeleev’s periodic table the number of inert gas elements discovered are :
(A) 1
(B) 8
(C) 3
(D) 0
Answer:
(D) 0

Question 28.
How many periods are there in the Mendeleev’s periodic table ?
(A) 7
(B) 10
(C) 6
(D) 14
Answer:
(A) 7

Question 29.
The similarity between the subgroup A and B elements is with respect to their :
(A) physical properties
(B) chemical properties
(C) valency
(D) none
Answer:
(C) Valency

Question 30.
Long form of periodic table based on :
(A) atomic number
(B) atomic mass
(C) number of neutrons
(D) none of these
Answer:
(A) atomic number

Question 31.
Which period contains the greatest number of metals?
(A) 1
(B) 2
(C) 3
(D) 4
Answer:
(D) 4

Question 32.
Which of the following elements belongs to the group that includes the most active metals?
(A) Aluminium
(B) Sodium
(C) Iron
(D) Mercury
Answer:
(B) Sodium

Question 33.
At the end of each period the valence shell is
(A) incomplete
(B) half filled
(C) singly occupied
(D) completely filled
Answer:
(D) completely filled

Question 34.
Hydrogen is called ?
(A) rogue element
(B) noble element
(C) transuranic element
(D) rare earth element
Answer:
(A) rogue element

Question 35.
Which of the following is a transuranic element ?
(A) Radium
(B) Neptunium
(C) Thorium
(D) Actinium
Answer:
(B) Neptunium

Question 36.
An element in second period whose electron affinity is zero is :
(A) Helium
(B) Argon
(C) Neon
(D) Krypton
Answer:
(C) Neon

Question 37.
Group 17 elements are also called as :
(A) alkali metals
(B) transition metals
(C) chalcogen
(D) halogen
Answer:
(D) halogen

Question 38.
which of the given elements A, B, C, D and E with atomic number 2,3,7,10 and 30 respectively belong to the same period?
(A) A, B, C
(B) B, C, D
(C) A, D
(D) A, C, E
Answer:
(B) B, C, D

Question 39.
The correct order of ionization potential is :
(A) Mg > Ar > Si
(B) Mg < Ar < i
(C) Mg > Si > Ar
(D) Mg < Si < Ar
Answer:
(D) Mg < Si < Ar

Question 40.
Which one is not a Dobereiner’s triad?
(A) Li, Na, K
(B) C, Si, Ge
(C) Ca, Sr, Ba
(D) Cl, Br, I
Answer:
(B) C, Si, Ge

Question 41.
Which one of the following is not a transition element?
(A) Fe
(B) Co
(C) Ca
(D) Cr
Answer:
(C) Ca

Question 42.
The atomic number of an element is 19. In modern periodic table, this element is placed in :
(A) First period
(B) Second period
(C) third period
(D) fourth period
Answer:
(D) fourth period

Question 43.
The element, which has zero electron affinity is third period is :
(A) Al
(B) P
(C) Ar
(D) S
Answer:
(C) Ar

Fill in the blanks :

1. The cause of periodicity of elements in the periodic table is that these elements have _______ configuration.
Answer:
similar.

2. The radioactive element among halogens is _______.
Answer:
astatine.

3. AIl the lanthanides and actinides belong to ________ group in the periodic table.
Answer:
3 or IIIB.

4. Inert gases have the general electronic configuration ________.
Answer:
n s² sp}⁶

5. The elements of s and p-blocks are collectively known as _______ elements.
Answer:
representative

6. First I.P. of nitrogen is ______ than that of oxygen.
Answer:
greater.

7. \(\mathbf{N a}^{\oplus}\) ion is _______ in size than Na-atom.
Answer:
smaller.

8. Strong electropositive elements are ______ good.
Answer:
reducing agents.

9. Ca²⁺ has a smaller ionic radius than K⁺because it has ______.
Answer:
higher nuclear charge.

10. The ionisation potential of an element ________ on moving from left to right in a period.
Answer:
increases.

11. On Pauling’s electronegativity scale, the element next to F is ______.
Answer:
oxygen.

12. Transition metal compounds are coloured because of ______.
Answer:
absorption of visible light.

13. Elements of group IA are called ______ metals.
Answer:
alkali.

14. Electronegativity or non-metallic character gradually ______ along a period from left to right.
Answer:
increases.

15. In a period, all the elements have the same number of electronic ______.
Answer:
shells.

16. Atomic size refers to the distance between the centre of nucleus and the ______ shell of an atom.
Answer:
outermost.

17. The vertical columns in which elements of similar physical and chemical properties occur in the periodic table are called _______.
Answer: groups.

18. Atomic number of an element is more ______ than its atomic weight.
Answer:
fundamental.

19. The term ‘periodic’ means _______ of anything at regular intervals.
Answer:
recurrence.

20. The elements belonging to zero group are chemically _______
Answer:
inert.

21. Hydrogen belongs to the ______ period.
Answer:
1 A (one).

22. Helium belongs to the ______ group.
Answer:
0 (zero).

25. The periodic table is seen to be divided into different horizontal series called _______.
Answer:
periods.

24. The elements in the modern periodic table are arranged in the increasing order of their _______.
Answer:
atomic number.

25. There are _____ elements in the fourth period of the periodic table.
Answer:
18.

26. The energy released when electron is added to a neutral gaseous atom is called ______ of the atom.
Answer:
electron affinity

27. Second period of periodic table contains ________ elements.
Answer:
8

28. Halogens are strong ______ agents.
Answer:
Oxidant

29. Along a period from left to right atomic radii ________.
Answer:
decreases

30. Name of a transitional element.
Ans:
copper

31. Across a period the number of ______ electrons increases by 1, while down the group they remain same.
Answer:
valence

32. All inert gases except _______ has 8 electrons in their outermost shell.
Answer:
helium

33. The basis of modern periodic table is _______ number.
Answer:
atomic

34. According to the modern periodic law, ________ of elements are a periodic function of their atomic number.
Answer:
properties

35. Group 3 to 12 contains elements known as ________ elements.
Answer:
transition

36. On going down a group in the periodic table, the size of atoms _______.
Answer:
increases

37. The incomplete period in the periodic table is _______.
Answer:
7th period

38. If an element has low tonization energy, it is likely to be _______.
Answer:
metallic

39. The elements in ______ are called alkaline earth metals.
Answer:
Group-2

40. The elements in group1 are called _______ metals.
Answer:
alkali

State whether the following statement is True or False : VSA

1. Mendeleev’s eka-silicon was later found to be silicon.
Answer:
False

2. An element with three electron shells and two valence electrons belongs to third period and Group two.
Answer:
True

3. A metal “X” is in the first group of the periodic table. The formula of its oxide is X₂O.
Answer:
True

4. All the elements of a particular group in the periodic table have the same number of valence electrons.
Answer:
True

5. On moving from left to right in a period of the periodic table, the size of the atom increases.
Answer:
False

6. Group 17 elements are called rare earth elements.
Answer:
False

7. The modern periodic table was prepared by Niels Bohr.
Answer:
True

8. In Lothar Meyer’s atomic volume versus atomic mass curve, the peaks are occupied by the alkali metals.
Answer:
True

9. On moving from left to right in a period, the electropositive character of elements decreases, but electronegeative character increases.
Answer:
True

10. Lithium, Sodium and Potassium form a Dobereiner’s triad.
Answer:
True

11. Lother Meyer pointed out that atomic volumes of solid elements are periodic functions of their atomic weight.
Answer:
True

Comprehensive WBBSE Class 10 Physical Science Notes Chapter 3 Chemical Calculations can help students make connections between concepts.

Chemical Calculations Class 10 WBBSE Notes

Accuracy: It refers to how close a measurement is to the true value.

Precision : It refers to how close one measurement is to another.

Scientific notation: The measurements of quantities in chemistry are spread over a wide range of 10^-31 to 10⁺²³. Hence, a convenient system of expressing the numbers in scientific notation is used.

Types of chemical reactions:

• Combination: e.g. Fe + S → FeS
• Decomposition: e.g. 2 KClO₃ → 2 KCl + 3 O₂
• Double Decomposition: e.g. AgNO₃ + NaCl → AgCl + NaNO₃
• Rearrangement or Isomerisation: e.g NH₄ CNO → NH₂ CONH₂ (Urea)
• Displacement: e.g. Zn + CuSO₄ → ZnSO₄ + Cu
• Polymerisation: e.g. n(CH₂ = CH₂) →(-CH₂-CH₂-)_n
• Neutralisation: e.g. HCl(aq) + NaOH(aq) → NaCl(aq) + H₂ O
• Redox Reactions : e.g. H₂ S + Br₂ → 2 HBr + S
• Catalytic Reactions: e.g. N₂ + 3 H₂ \(\stackrel{\mathrm{Fe} / \mathrm{Mo}}{\rightleftharpoons}\) = 2 NH₃
• Plastic catalytic Reactions: Which require light as well as a catalyst to take place e.g. manufacture of starch and sugar by plants from CO₂ and H₂O in presence of light and chlorophyll (catalyst)

Laws of chemical combination:

• Law of conservation of Mass: (A. Lavoisier, 1774)
• Law of Definite proportions: (Louis Proust, 1799)
• Law of Multiple proportions: (John Dalton, 1804)
• Law of Reciprocal proporticns: (Richter, 1792)
• Gay Lussac’s Law of Gaseous volumes: (Gay Lussac, 1809)
• Dalton’s Atomic Theory: (John Dalton, 1803)

Atomic mass: It is the average relative mass of an atom of an element as compared to the mass of a carbon atom (12_c) taken as 12.

Atomic mass unit: It is the quantity of mass equal to \(\frac{1}{12}\) th of the mass of a carbon atom ( ¹²C). 1 amu = 1.6605 × 10^-24 g

Carbon atomic mass: It is the atomic mass of an element expressed in gram.

Kelation among atomic mass, equivalent weight and valency:

Atomic mass = Equivalent weight × Valency

Avogadro constant: The number of atoms or any other particles present in a given system is expressed in the terms of Avogadro constant. (6.022 × 10²³)

Molar volume: The volume of gaseous substance (element or compound) under a fixed temperature and pressure is known as volume of the gas.

Mole (SI system): A mole is the amount of substance which contains as many entities (atoms, molecules, ions or any other particle) as there are atoms in exactly 0.012 Kg (or 12 g) of the carbon -12 isotope.

Empirical formula: It is the formula of a compound which gives the simple whole number of ratio of the atoms of various elements present in one molecule of compound.

Molecular formula; It is the formula of a compound which gives the actual number of atoms of various elements present in one molecule of the compound.

Structural formula: A formula which gives the actual arrangement of the different atoms in the molecule are linked together is called a structural formula of the compound.

Percentage of an element: Percentage of an element in a chemical compound is the number of parts by weight of it present in 100 parts by weight of the compound.

Mass-mass relationship problems: In this type of problems mass of one of the reactants/products is to be calculated if that of the other reactants/products are given.

Limiting reactant: The reactant which is completely used and determines the amount of product formed is known as limiting reactant.

Theoretical yield: The theoretical yield of a product is the maximum yield obtainable as calculated on the basis of the amount of limiting reactant used.

Percent yield: Percent yield which is the ratio of the actual yield to the theoretical yield multiplied by 100.

Stoichiometry: The quantitative study of the reactants required or the products formed is called stoichiometry.

Dulong and Petit’s Law: It states that ‘the product of atomic weight and specific heat of an element is approximately equal to 6.4.

Isomorphism: Substances having same crystalline structure are said to isomorphous. e.g. ZnSO₄.7 H₂O and FeSO₄.7 H₂O

Vapour density: It is the ratio of the mass of a certain volume of the gas to the mass of same volume of hydrogen under similar conditions of temperature and pressure.

Relation between molecular weight and vapour density :
Molecular weight = 2 × Vapour density

Relation between empirical formula and molecular formula.
Molecular formula = n × Empirical formula
(n = a simple whole number and
may have values 1,2,3,…)

Equivalent weight: It is the number of parts of a substance which combine with or displace directly or indirectly 1.008 parts by weight of hydrogen or 8 parts by weight of oxygen or 35.5 parts by weight of chlorine.

Atomicity of a gas: It is the number of atoms present in one molecule of a gaseous element.

Solubility: The amount of solute in grams that can be dissolved in 100 grams of a solvent to form a saturated solution at a definite temperature is called the solubility.

Percentage by weight [%(w/w)]: It is the amount of solute in grams present in 100 grams of the solution.

Weight/volume percentage [%(w/v)]: It is the amount of solute in grams present in 100 mL of the solution.

Volume/volume percentage [%(v/v)]: It is the volume in mL of the solute percentage in 100 mL of the solution.

Normality (N): It is the number of gram equivalents of solite dissolved per litre of a solution.

Molarity (M): It is the number of moles of solute dissolved per litre of the solution.

Formality (F): It is the number of gram formula weight of the ionic solute dissolved per litre of the solution.

Molality (m): It is the number of moles of solute dissolved in 1000 g of the solvent.

Mole fraction: It is the ratio of the number of moles of one component to the total number of moles of substances in the solution.

Parts per million (ppm.): It is defined as the number of parts of a component per million parts of the solution.

The following equations are generally used for weight-weight calculation.

2 KClO₃ = 2 KCl + 3 O₂
Zn + H₂ SO₄ = ZnSO₄ + H₂
CaCO₃ = CaO + CO₂
2 NH₄ Cl + CaO = 2 NH₃ + CaCl₂ + H₂O
Mg + H₂ SO₄ = MgSO₄ + H₂
CaCO₃ + 2 HCl = CaCl₂ + H₂O + CO₂
2 H₂ + O₂ = 2 H₂O

Comprehensive WBBSE Class 10 Physical Science Notes Chapter 8.2 Ionic and Covalent Bonding can help students make connections between concepts.

Ionic and Covalent Bonding Class 10 WBBSE Notes

Chemical Bond: The chemical force that hold the atoms together in a molecule is called the Chemical Bond.

Cause of chemical bonding

1. Tendency to acquire noble gas configuration: From the electronic configuration of the noble gases it is clear that all noble gases (except helium) have eight electrons in their valence shell i.e. they have ns², np⁶configuration.

The noble gas configurations are highly stable and have no tendency to lose or gain electrons. Thus, inert nature of noble gases is due to their stable electronic configuration.

Atoms of all other elements do not have eight electrons in their valence shall (outermost orbit).
Therefore, atoms of these elements combine with other or with atoms of other elements to acquire stable configuration of the nearest noble gas (according to octet rule).

This tendency of atoms of various elements to acquire stable configuration of the nearest noble gas is the cause of chemical combination.

2. Tendency to acquire minimum energy: All systems tend to attain stability by lowering their potential energy. Increase in attractive forces leads to decrease in energy. Conversely, decrease in attractive force or increase in repulsive forces increases energy.

Let us now apply these principles to bonding between atoms. Even, atom bies to attain a state of minimum energy. When two atoms are brought closer to form a molecule, following forces come into play.

Attractive forces between electrons of one atom and nudeus of other. Repulsive forces due to inter-electronic and inter-molecular repulsive forces. The molecule becomes stable when there is a net increase in the attractive force. This Increase in attractive force results in decrease energy. Greater the decrease in energy, more stable the molecule will be.

• Electronic theory of valency: According to electronic theory (developed by Kosel and Lewis. 1916) the valency of on element is the number of electrons that its atoms can gain, lose or share to acquire stable nearest noble gas configuration.

Depending upon the mode of acquiring nearest noble gas configuration, there are three common types of bonds.

• Ionic or Electrovalnet bond
• Covalent bond
• Co-ordinate or Dative bond.

Apart from these chemical bonds, there are some physical bonds (which are electrosintic in nautre). The main types of physical bonds are:

• Hydrogen bond
• Metallic bond
• Vander Waai’s interactions

(a) ionic bonding :

The electrostatic force of attraction which holds the oppositely charged ions together is known as ionic bond or electrovalent bond and the compounds which are formed by the transference of electrons from one atom to the other are called ionic or electrovalent compounds. The number of electrons which an atom loses or gain while forming an ionic bond is known as its electrovalency.

Conditions necessary for the formation of ionic bond

• Formation of cation from a neutral atom having low ionisation energy.
• Formation of an anion from an anion from a neutral atom with high value of electron affinity.
• Formation of crystal lattice from oppositely charged ions involving large release of energy. Higher the Lattic energy of a crystal, more readily it will get formed.

Characteristics of Ionic Compounds:

• All ionic compounds are usually crystalline solids and are composed of ions even in the solid state.
• Ionic solid have high melting points and boiling points due to the presence of strong attractive forces between the oppositely charged ions.
• These are highly soluble in polar solvents (such as water) haveing high dielectric constant but insoluble in organic solvent (such as benzene, alcohol, ether etc.)
• Ionic compounds have low volatility, high density and high stability.
• In molten state or in solution in polar solvents, ionic compounds are good conductors of electricity.
• In solution, ionic compounds undergo ionic reactions which are very fost.
• Crystals of certain Ionic compounds have similar arrangement of atomns as well as geometry.
• Ionic bonds are non-directional and due to the non-directional nature of ionic bonds, ionic compounds do not show isomerism.
• Ionic compounds are hard and brittle

(b) Covalent Bond (Lewis Concept) :

A covalent bond is formed by the mutual sharing of electrons between the atoms, both of which are short of electrons. The compound so formed is called covalent compound. The number of electrons contributed by an atom for sharing is called its covalency. Depending upon the number of electrons shared between two atoms being one, two or three, we have single covalent bond ( : or -), double convalnt bond ( : : or = ) and triple convalent bond ( or ).

Characteristics of Covalent Compounds:

• Covalent compounds exist in solid, liquid or gaseous state.
• Covalent compounds like napthalene in which molecules are held together by weak Vander Waal’s forces, have low melting points and boling points.
• Covakrnt bonds are rigid and directional in nature.
• Covalent solids like diamond, Si, C etc. consisting of giant molecules are bad conductors of electricity due to the absence of free electrons or ions.
• Since i.e dissolves like, polar covalent compounds like sugar are soluble in polar solvents like water and the non-polar compounds like naphthalene are more soluble in non-polar solvents Like benzene.
• Covalent compounds are neither hard nor brittle like ionic compounds.
• Covalent compounds undergo molecular reactions in solution.

Examples of covalent compounds and their structures:

Factors affecting the formation of ionic bonds :

• The ionization energy of the electropositive element should be low i.e. the metal atoms form a low charged positive ion easily.
• The quantitative value of electron affinity of electronegative element should be high i.e. the non-metal atom is small and give rise to low charged negative ion easily.
• Lattice enthalpy should be high.

Lattice enthalpy : The energy given off when gaseous positive and negative ions together to form 1 mole of the solid ionic compound is called Lattice enthalpy (U)
Na⁺ (g) + Cl(g) → NaCl (s)    ΔH = -U
For the reverse process, NaCl (s) → Na⁺(g) + Ch(g)    ΔH = +U
Lattice enthalpy a charge of ions
Lattice enthalpy \(\alpha \frac{1}{\text { size of ions }}\)

Lattice enthalpy play an important role in deciding the solubility of ionic solids.

• If the anion and the cation are of comparable size, the cation radius will influence the lattice energy. Since lattice energy decreases much more than the hydration energy with increasing ionic size, solubility will increase as we go down the group.
• If the anion is large compared to cation, the lattice energy will remain almost constant within a particular group. Since, the hydration energies decrease down a group, solublity will decrease as found for alkaline earth metal carbonates and sulphates.
• Born-Haber cycle : The fundamental of this cycle is based upon the fact

Example :
According to Hesse’s law

Thus, lattice energy of Nacl(S) has a large negative value. This indicates that the compound is highly stable.
Finding the number of covalent bonds.

Finding the number of covalent bond electron shored
Number of covalnent bonds between two atoms = \(\frac{\text { electron shored }}{2}\)
Total number of shared electrons S = N – A

S = the total number of electrons shared in the molecule or polyatomic ion.
N the number of valence shell electrons needed by all the atoms in the molecule or ion to achive noble gas configuration [ N = 8x] number of atoms ( H excluded) + 2 x number of H-atoms]
A = the number of electrons available in the valnece shell of all of the representative atoms. This is equal to the sum of their periodic group number.
e.g. in CO₂ for 0-atom, A = 6 and for C-atom, A = 4
Thus A = 4+2 x 6 = 16
N = 8 x 3=24
S = 24 – 16 = 8
Thus, there are eight electrons shared to form bonds.
: Ö : : C : : Ö :
Formal charge: The atoms of a molecule or ion are usually neutral i.e. carry no charge for some purposes, such as to find reaction mechanism,assigning of formal charge of atoms in a molecule or ion is important.

• Favourable factors for covalent bonding (Fajan’s rule)

(i) The charge on cation or anion must be larger. The increased charge will increases the polarisation of the other ion (anion), thus covalent character is increased.

(ii) The cation must be smaller because in the fact, the charge possess will be more concentrated, thus causing more polarisation of anion. Hence we can say that ionic compounds having smaller cations show more covalent nature.

(iii) The anion must be larger. In such anions, the aoter electrons will be at a greater distance from the nucleus, hence more easily influenced by the attractive forces of cation. As the result larger anions will be more easily polarised in comparison to smaller anions.

(iv) The polarising power of those cations which donot have inert gas configuration will be more in comparision to cations having inert gas configuration.

• Some important covalent bond parameters :

(i) Bond length: The average distance between the centre of nuclei of the two bonded atoms in a molecule is known as bond length. It depends upon the size of atoms hybridization, steric effect, resonance etc.

(ii) Bond enthalpy: Bond enthalpy is the amount of energy required to break a particular bond in one mole of gaseous molecule.
Bond enthalpy α electronegative

(iii) Bond order : It is the number of covalent bonds present between the two atoms in a molecule.
order a bond enthalpya bond length
Bond order a bond enthalpy α \(\frac{1}{\text { bond length }}\)

(iv) Bond angles : It is the angle between the bonded orbitais. Generally it decreases, as the number of lone pair of electrons increases, or as the electronegativity of the central atom decreases.

However, in molecule having same central atom, bond angle increases as the electronegativity of surrounding atom decreases.

∴ The order of eledronegativity is CI > Br > I

• Type of covalent Bonds:

(i) Non-Polar Conalnt Bond : If the covalent bond is formed between two homonuclear atoms i.e. between atoms of exactly equal electronegativity, the electron pair is equally shared between them. Such a bond is called non-polar covalent bond, e.g. H₂, Cl₂, F₂  etc.

(ii) Polar covalent bond : If the bond forming entities are dissimilar i.e. heteronuclear or with different electronegativity, the bond formed has partial ionic character as the electron pair is attracted by more electronegative entity. Such a bond is called polar covalent bond.

The greater difference in electronegativity higher is the polar nature.

Electronegativity : The electronegativity of an element is the tendency or ability its atom to attract the bonding or shared pair of electrons towards itself in a covalent bond. The relative order of electro negativity of some important element is:

Electronegativity is maximum in : F (4.0)
Electronegativity is minimum in: Fr (0.7)

Co-ordinate bond:
A Co-ordinate bond is a special type of covalent bond in which the shared pair of electrons is contributed by one of the two combining atoms. A Co-ordinate bond is represented by an arrow ( – ) pointing from the donor towards the acceptor.
Example:

Characteristics of co-ordinate compounds :

• The compounds exhibit all three states i.e. solid, liquids and gases under ordinary conditions.
• The melting and boiling points of these compounds and higher as compared to covalent compounds but lower than those of ionic compounds.
• Like covalnent compounds these are also poor conduction of electricity in solid as well as fused state.
• These compounds are sparingly soluble in polar solvent like water, however, these are readily soluble in organic solvent.
• Compounds are generally as stable as covalent compounds. The addition compounds are not very stable.
• Co-ordinate linkage is rigid and directional, thus compounds exhibit isomerism.
• Cd-ordinate compounds show molecular reactions just like covalent compounds.
• The dielectric constants of these compounds are higher.

Dipole moment : The product of the magnitude of positive or negative charge (q) and the distance (d) between the centres of positive and negative charges in a polar molecule is called dipole moment.
μ = q x d (p = Dipole moment)

The unit of dipole moment in CGS system in debey and in SI system is Coulomb-metre.

Dipole moment is a vector quantity, thus indicated by the symbol (+→) pointing towards the negative end e.g.

For symmetrical molecules, dipole moment, dipole moment is zero but unsymmetrical molecules have some dipole moment e.g.

However symmetric molecules like HF, H₂O, NH₃, have some dipole moment

By using dipole moment, the precentage ionic character of a polar bond (A-B) is calculated as,

Resonance: The various Lewis structures, which differ in the positions of non-bonding or π-electrons but not in the relative positions of atoms are called resonance structures contributing structure or canonical forms and this concept is known as resonance.

Example : Benzene molecule can be represented as a resonance hybrid (III) of two kekule structures, (I) and (II).

\(\mathrm{BO}=\frac{\text { total number of bonds between two atoms in all the structures }}{\text { total number of canonical forms }}\)

The stability of a resonance structure can be decided by considering the following points-

• A non-polar canonical form is more stable.
• More the number of covalent bonds, more is the stability.
• Resonance structure in which negative charge resides on electronegative atom and positive charge on electropositive atom and positive charge on electropositive atom is more stable as compared to that for which opposite is true.
• Hydrogen bond The electrostatic force of attraction existing between the H-atom covalently bonded to an electronegative atom (F, O or N) in a molecule and the electronegative atom of another molecule (similar or different type) is known as hydrogen bond.

Types of hydrogen bonding

(i) Intermolecular hydrogen-onding : When hydrogen bonding occurs between different molecules of the same or different compounds, it is called intermolecular hydrogen bonding.
Example:

(ii) Intramolecular hydrogen bonding : When hydrogen bonding takes place within the same molecule, it is called intramolecular hydrogen bonding.
Examples :

• Hybridisation : It may be defined as the process of inter mixing of atomic orbitals of the same atom having same or slightly different energies so as to redistribute their energies and give new orbitals of equal energies and identical shapes.

• Types of hybridisation :

Determination of hybridisation of the central atom
H = \(\frac{1}{2} [V+X – C . A ]\)
H = Number of orbitals involved in hybridisation ;
V = Number of electrons in the valence shell of the central atom ;
X = Number of monovalent atoms surrounded the central atom ;
C = Change on cation.
A = Change of anion.

Difference between Electrovalent and Covalent Compounds :

Electrovalent Compound	Covalent Compound
1. These are formed by the transfer of one or more electrons from one atom to another. 2. These consist of ions. 3. These are soluble in water but insoluble in organic solvents. 4. These are hard solids with high melting and boiling points. 5. These conduct electricity in fused as well as aqueous solutions. 6. These undergo ionic reactions which are very fast. 7. These do not show isomerism.	1. These are formed by the sharing of one or more electrons between the bonded atoms. 2. These consist of invidual molecules. 3. These are isoluble in water but solute in organic solvents. 4. These exist as gases, liquids or soft solids with low melting and boiling points. 5. These do not conduct electricity. 6. These undergo molecular reactions which are very slow. 7. These show isomerism.

Comprehensive WBBSE Class 10 Physical Science Notes Chapter 2 Behaviour of Gases can help students make connections between concepts.

Behaviour of Gases Class 10 WBBSE Notes

Matter: It is classified into three States: Solid, liquids and gases.

Some Physical properties of gases:

Motion of gas molecules: A gas is composed of infinite number of molecules. Molecules of gaseous substances move almost freely and exhibit random motion in all directions.

Shape and Volume: A gas has niether a definite shape nor a definite volume. It takes the shape and volume of the container in which it is kept.

Density: Gases have lower density than the liquids and solids.

Diffusion: When two or more gases which do not react with each other, are brought in contact, they intermix with one another forming a homogeneous mixture. This spontaneous mixing of gases with one another is known as diffusion.

Expansibility: Gases exhibit unlimited power of expansion.

Compressibility: The compressibility of a gas is very high.

Temperature of a gas: Temperature of any gas is the measure of average kinetic energy of the gas molecules.

Pressure of a gas: The force exerted by the gaseous molecules per unit area of the wall due to continuous collision of the gas molecules with the walls of the container is called the pressure of the gas.

• Unit of area: CGS unit : cm²
• SI unit : m²
• Unit of force: CGS unit : dyne
• SI unit : Newton

Unit of pressure:

• The pressure of gas is generally expressed in the unit of atmosphere (atm).
• Torr: Pressure exerted by exactly 1 mm of mercury column at 0°C and at standard gravity is termed as 1 torr.
• Bar: The commonly used unit of pressure = bar

1 atm = 1.01325 bar

Pascal (Pa) : SI unit of pressure is pascal. The pressure exerted when a force of 1 newton acts on 1 m² area is called 1 pascal.

1 atm = 76.0 cuHg = 760 mm Hg = 760 torr

psi : The pressure is also expressed in the unit of pound per square inch or psi.

1 atm = 14.7 psi

Measurement of pressure exerted by a gas : Very common instrument used for measuring the pressure of gas is manometer.

Pressure (P) = \(\frac{\text { Force }}{\text { Area }}\) = \(\frac{\mathrm{A} \times \mathrm{h} \times \mathrm{d} \times \mathrm{g}}{\mathrm{A}}\) = hdg

Unit of volume : At a particular temperature and pressure the volume of a gas closed in a container is equal to the volume of that container at the same temperature and pressure.

• Units : SI units of volume : m³
• Smaller units : dm³, cm³
• The symbol used for litre is : L
• The symbol used for millilitre is : mL

The relationship among different units are :

1 L = 10³ mL=10³ cm³=10³ ×(10^-1)³ dm³ = 1 dm³
1 m³=10⁶ cm³=10³ dm³=10³ L.

NTP or STP (Normal or Standard Temperature and Pressure): It is defined as the pressure exerted by column of mercury 76 cm in height at 0°C at 45° latitude and mean sea-level.

Boyle’s law (1662): At constant temperature, the volume of a given mass of a gas in inversely proportional to the pressure of the gas.

Mathematical expression of Boyle’s law: Let the pressure of a definite mass of a gas be P and the volume be V. If the temperature of T K (kelvin), then according to Boyle’s Law,

V ∝ \(\frac{1}{P}\)

when temperature T and the mast.
remain constant.
or, V = K.\(\frac{1}{P}\) when temperature T and the mass of the gas ‘m’ remain constant.
or, V = K.\(\frac{1}{P}\) (K = Proportionality Constant)
∴ PV = K, this equation is the mathematical expression of Boyle’s law.

Graphical representation of Boyle’s Law :

At constant temperature plot of P vs. V for a definite mass of gas.

At constant temperature plot of P V vs. P for a definite mass of gas.

At constant temperature plot of \(\frac{I}{V}\) vs. P and V vs. \(\frac{1}{P}\) for a definite mass of gas

At constant temperature plot of log P vs. log V for a definite mass of gas

Isotherms: These are the pressure volume curves obtained at constant temperature.

Charle’s Law (1787): At constant pressure, the volume of a given mass of a gas increases or decreases by \(\frac{1}{273}\) of its volume at 0° C for each one degree rise or fall in temperature.

Mathematical expression of Charle’s law :

(V₀ = Volume of a given mass of gas at Constant pressure at 0°C
V_t = Volume of the gas after t°C rise of temperature)

Absolute zero : According to Charle’s law: At constant pressure, the temperature (-273°C) at which, theoretically a gas would have no volume, is known as absolute zero. A temperature below this cannot be conceived of in the universe.

Absolute scale of temperature : It is a thermometric scale where -273°C is the starting point i.e. on this scale 0 K is equal of -273° C and each degree is equal to that in the celsius scale.

Alternative Statement of Charle’s law : The volume of a given mass of a gas is directly proportional to the absolute temperature if the pressure remains constant.

Mathematical expression of Charle’s law with respect to absolute temperature.

V ∝ T at constant pressure and a definite mass of gas.
or, V = KT
or, [\(\frac{V}{T}\) = K = const

Graphical representation of Charle’s law

At constant pressure, plot of \(\frac{V}{1}\) vs. T for a definite mass of gas.

At constant pressure plot of V vs. t°C for vs. T for a definite mass of gas. definite mass of gas plot of V vs. t°C

At constant pressure plot of log V vs. log T for a definite mass of gas.

Graphical representation of P vs T at constant volume and for a definite mass of gas- According to Gay-Lussac’s law.

Combined form of Boyle’s and Charle’s law :
Let us consider for a definite mass of a gas the pressure, temperature and volume are P, T and V respectively.

According to Boyle’s Law

V ∝ \(\frac{1}{P}\) (at constant temperature and for a given mass of the gas)
According to Charle’s law
V ∝ T (at constant pressure and for a given mass of the gas)
According to the laws of joint variation,
V ∝ \(\frac{T}{P}\) when the mass of the gas remains constant but both pressure and temperature of the gas vary.
∴ V = K.\(\frac{T}{P}\)

(K = proportionality constant and it depends upon the amount of gas)
or, PV = KT
This equation is the combined form of Boyle’s law and Charle’s law.

Ideal gas: A gas which obeys Boyle’s law, Charle’s law and Avogadro’s law for all volumes of temperature and pressures and which obeys the equation of state P V=n R T under all conditions of temperature and pressure is called an ideal gas.

Real gases: The gases which do not obey PV=n R T equation are called real gases.

The compressibility factor (Z)
\(\left(Z=\frac{P V}{n R T}\right)\) of an ideal gas = 1

All gases approach the ideal behaviour as the temperature goes further from their boiling points i.e. at high temperature and low pressure.

Gay-Lussac’s Law: Under the same conditions of temperature and pressure two or more gases combine chemically in simple ratios by volumes of and the volumes of the products if gaseous also bear a simple relation to the volumes of the reacting gases.

Berzelius hypothesis: Under the same conditions of temperature and pressure equal volumes of all gases contain the same number of atoms.

Avogadro’s Law: Under the same conditions of temperature and pressure, equal volumes of all gases (element or compound) contain the same number of molecules.

Avogadro’s Number: Avogadro’s number may be defined as the number of molecules present in one gram-mole of any substance, element or compound (solid, liquid or gas).
N = 6.022 × 10²³, R.A. Millikan determined the value by oil drop experiment in 1913.

Molar volume: The volume occupied by one gram-molecule of any gaseous substance (elementary or compound) at a fixed temperature and pressure is known as the molar volume.
At standard conditions of temperature and pressure (STP), the volume equal to 22.4 litres is the molar volume of all gases.

Substance	Molecular mass
H2O	2 × 1 + 16 = 18
N2	14 × 2 = 18
O2	16 × 2 = 32

Pressure of dry gas = Atmospheric pressure – Aqueous tension

Equation of state for an ideal gas :
According to Boyle’s law, V ∝ \(\frac{1}{P}\) (T and n are constant)
According to Charle’s law, V ∝ T (P and n are constant)
According to Avogadro’s law, V ∝ n (P and T are constant)
By method of compound variation
V ∝ \(\frac{n T}{P}\) when P, T and n of the gas vary
or V = \(\frac{R n T}{P}\) (R = molar gas constant )
or, PV = nRT
This equation is called ideal gas equation.

Calculation of molar mass from equation of state

PV = nRT
[Let the mass of the gas = wg
Molecular mass of the gas = M

Dimension of Molar gas constant R

R = energy K^-1 mol^-1

Values of R in different units

Unit	Volume of R
L-atm	0.0821 L–atm mol -1K-1
Cal 1	1.987 Cal-1 K-1
SI	8.314 J mol-1 K-1
CGS	8.314 × 107 erg-1 mol-1 K-1
Dm3.torr	62.36 dm3 .torr. mol -1 K-1
Dm3.kPa	8.314 dm3.Pa.mol-1 K-1

Boltzmann constant (K)

Determination of density and molar mass of an ideal gas : For n moles ideal gas, the equation of state is :

PV = nRT, n = \(\frac{m}{\bar{M}}\)

(If ‘m’ and ‘M’ are the mass of the gas in gram and molar mass of the gas respectively, then the number of moles of gas n = \(\frac{m}{\bar{M}}\))

The above equation indicates the relation among the density, pressure, absolute temperature and moiar mass of an ideal gas.

Dalton’s law of partial pressure: At constant temperature, when two or more non-reacting gases are er:closed together in a container of definite volume, the total pressure of a mixture of gases is equal to the sum of the partial pressures of the constituent gases.

P_Total= P₁ + P₂ + P₃ +…

Diffusion of gas: The process of the property by virtue of which two or more gases without any external help intermix with each other spontaneously to form a homogeneous gas mixture irrespective of their densities or molar masses is termed as diffusion of gas.

Effusion: The process of out-flow of a gas confined in a closed vessel under high pressure through a fine orifice (hole) made in the well of the vessel is called effusion.

Graham’s Law of diffusion: At constant temperature and pressure, the rate of diffusion of any gas in inversely proportional to the square root of its density.

\(r ∝ [latex]\frac{1}{\sqrt{d}}\) or, r = \(\frac{K}{\sqrt{d}}\)

(r = the rate of diffusion or effusion of gas,
d = the density of gas, K = proportionality constant)

Postulates of kinetic theory of gases:

• All gases consist of very large number of tiny particles called molecules that are in constant rapid motion.
• The gas molecules are perfectly round, very hard and separated by large distances. Their actual volume is thus, negligible as compared to the total volume of the gas.
• The gas molecules collide with one another and with the walls of the container. The pressure exerted by a gas is due to the bombardment of its molecules on the walls of the vessel.
• The collisions between the gas molecules are perfectly elastic, i.e. there is no loss of energy during these collisions.
• The distance between the gas molecules being very large, there is no effective force of attraction or repulsion between them.
• The gas molecules move freely in all directions. Their speed and direction change continuously due to collisions among them. As a result, their motion becomes zig-zag or random.
• The average kinetic energy of the gas molecules is directly proportional to the absolute temperature of the gas.

Influenre of pressure on volume occupied by a gas; effect of temperature on the spond of gas molecules and on the pressure exerted by the gas:

• If the velocities of the molecules increase, the magnitude of pressure increases and if velocities of them decrease, pressure decreases.
• The motion of gas molecules depends on temperature of the gas. If the temperature is increased, the velocity of the gas molecules or the kinetic energy of the gas molecules increases.

Deviation from Ideal behaviour :

The modified equation put forward by Vander Waals’ for one mole of a real gas as:

\(\left(P+\frac{a}{V^2}\right)\) (V-b) = RT

and for ‘n’ moles of the gas it is expressed as

\(\left(P+\frac{a n^2}{V^2}\right)\) (V-nb) = nRT

where ‘a’ and ‘b’ are constants called Vander Waals’ constants. The values of constants ‘a’ and ‘b’ depend upon the nature of the gas.

Comprehensive WBBSE Class 10 Physical Science Notes Chapter 8.3 Electricity and Chemical Reactions can help students make connections between concepts.

Electricity and Chemical Reactions Class 10 WBBSE Notes

Electrochemistry: The branch of chemistry which deals with the relationship between chemical energy and electrical energy and how one can be converted into another.

Conductors: A substance which allows the electric current to flow through it is known as a conductor, e.g. Cu, Ag, Au etc.

Non-conductors: A substance which does not allow the electric current to flow through it is known as non-conductors.

Type of conductors :
(i) (a) Metallic conductors e.g. Cu, Ag, Au etc.
(b) Non-metallic conductors e.g. graphite (carbon)
(ii) Electrolytes

(a) Metallic conductors: These are the substances (metals) which allow the current to pass through them but do not undergo any change in themselves.

(b) Electrolytes: Compounds which in the fused state or in aqueous solution can conduct electricity and are decomposed chemically yielding new substances are known as electrolytes.

Non-electrolytes: Compounds which in the fused state or in aqueous solution do not conduct electricity are known as non-electrolytes, e.g. pure water, alcohol, acetone, sugar, urea etc.

Electrolytes: It is the process of chemical decomposition of an electrolyte in solution or in the fused state by the passage of electric current.

Electrodes: Two conducting metal plates or graphite strips or rods, placed in a voltameter to pass electric current through the electrolyte during electrolysis are called electrodes.

Anode: The electrode through which current enters into the voltameter is connected to the positive terminal of a battery is called anode.

Cathode: The electrode, which is connected to the negative terminal of the battery is called the cathode.

Voltameter: The complete set up or vessel consisting of two metal plates and electrolytes in which electolysis takes place is called Voltameter.

Ions: For the passage of electricity, electrolytes are decomposed reversibly into charged particles. These charged particles are called ions.

Cation: The positively charged particles are migrated towards cathode and is called cation
e.g. H⁺, Na⁺, NH₄⁺ etc.

Anion: The negatively charged particles migrated towards anode is called anion,
e.g. Cl^–, SO₄^2-, NO₃^– etc.

Difference between Metallic conduction and Electrolytic conduction

Metallic conduction	Electrolytic conduction
1. Flow of electricity is due to the movement of electrons only and there is no movement of matter. 2. Flow of electricity takes place without the decomposition of the substance. 3. The electrical conduction decreases with increase of temperature.	1. Flow of electricity is due to the movement of ions and hence there is transfer of matter. 2. Row of electricity is accompanied by the decomposition of the substance (electrolyte). 3. The electrical conduction increases with increase of temperature.

Strong electrolytes : Those electrolytes which are ionised almost completely in the fused state or in aquous solution, are known as strong electrolytes, e.g. NaOH, NaCl, HCl, H₂SO₄

• Weak electrolytes : Those electrolytes which are ionised a little are called weak electrolytes
e.g. HCN, NH₄OH, CH₂COOH etc.

Difference between Atom and Ion :

Atom	Ion
1.  Atom is a neutral, smallest and active particle of element. Number of electrons and protons are same in atom.	1. Number of protons are not equal with number of electrons in ion.
2. Atoms do not exist in free state.	2. Ions exist in free state.
3. Chemically atoms are more reactive.	3. Ions are not reactive.

Electrolysis of some electrolytes:

Electrolysis of water:
Voltameter : Two platinum plates are introduced through a rubber cock attached in the bottom of glass vessel.
Electrodes : Two platinum plates.
Electrolyte : Water acidified with a few drop of dilute H₂SO₄.
Procedure : Two hard glass tube are filled with water. They are inverted over the two electrodes. When electric current is passed through the electrodes from a battery into the acidified water, electrolysis takes place. Gases (hydrogen and oxygen) are collected in the tube by the downward displacement of water.
It shows from experiment that gas collected in anode is oxygen and that collected in cathode is hydrogen.

Electrolytic reaction:

(iii) Reaction in cathode : H⁺+e → H; H + H → H₂↑
(iv) Reaction in anode : OH^– – e → OH ; 4OH → 2H₂O + O₂↑
Conclusion: In the electrolysis of water, it is found that at the same tem­perature and pressure one volume of oxygen (O₂) and two volumes of hydrogen (H₂) are evolved.

2. [Electrolysis of sulphuric acid
(a) Electrolysis of dilute sulphuric acid :
Electrodes: Two platinum plates

• Electrolytic reaction :

(b) Electrolysis of conc. H₂SO₄ (60%):

Conclusion : In the electrolysis of conc. H₂SO₄ (60%) it is found that at low temperature hydrogen gas is evolved at cathode and H₂O₂ is produced at anode.

3. Electrolysis NaCl
(a) Electrolysis of fused NaCl :
Electrodes :
Cathode — Platinum
Anode — Graphite

Electrolytic reaction :
(i) Decomposition of NaCl : NaCl \(\rightleftharpoons\) Na⁺ + Cl^–
(ii) Reaction in Cathode : Na⁺ + e \(\rightleftharpoons\) Na
(iii) Reaction in anode : Cl^– – e → Cl; Cl + Cl → Cl₂↑

Conclusion: In the electrolysis of fused NaCl It is found that sodium is produced at cathode and chlorine is evolved at anode.

(b) Electrolysis of dilute aqueous solution of NaCl :
Electrodes :
Cathode — Platinum
Anode — Platinum

Electrolytic Reaction:
(i) Dissolution of NaCl : NaCl \(\rightleftharpoons\) Na⁺ + Cla^–
(ii) Dissolution of water : H₂O \(\rightleftharpoons\) H⁺ + OH^–
(iii) Reaction in cathode : H⁺ + e → H; H + H → H₂↑
(iv) Reaction in anode : OH^– – e → OH; 4OH → 2H₂O + O↑

Conclusion : In the electrolysis of dilute aqueous solution of NaCl it is found that hydrogen is evolved at cathode and oxygen is produced at anode.

Electrolysis of cone aqueous solution of NaCl:

Electrodes :
Cathode — Graphite
Anode — Graphite

Electrolytic reaction :
(i) Dissolution of NaCl : NaCl \(\rightleftharpoons\)  Na⁺ + Cl^–
(ii) Dissolution of water : H₂O \(\rightleftharpoons\) H⁺ + OH^–
(iii) Reaction in Cathode : H⁺ + e → H; H + H → H₂↑
(iv) Reaction in Anode : Cl^– – e → Cl ; Cl + Cl → Cl₂↑
(v) Part of Cl₂ produced at anode reacts with NaOH;
2NaOH + Cl₂ = NaCl + NaOCl + H₂O (which is produced in solution)

4. Electrolysis of aqueous solution of copper sulphate :
(a) Using platinum electrodes :

Electrodes :
Cathode — Platinum
Anode — Platinum

Voltameter : An iron pot is used for electrolysis.
Electrolyte : Aqueous solution of copper sulphate

Electrolytic reaction:
(i) Dissolution of CuSO₄ : CuSO₄ \(\rightleftharpoons\)Cu²⁺+ SO₄²
(ii) Dissolution of water : \(\rightleftharpoons\) H⁺ + OH^– – Cu²⁺ + 2e
(iii) Reaction in cathode : Cu²⁺ + SO₄²
(iv) Reaction in anode : OH^– – e → OH; 4OH → 2H₂O + O₂↑

Conclusion : In the electrolysis of aqueous solution of copper sulphate using platinum electrodes, it is found that copper is deposited at cathode and oxygen is evolved at anode and the final solution becomes acidic due to the formation of sulphuric acid (H₂SO₄).

(b) Using copper electrodes :
Electrodes :
Cathode – Copper
Anode – Copper

Voltameter : An iron pot is used for electrolysis.
Electrolyte : Aqueous solution of copper sulphate

Electrolytic reaction:
(i) Dissolution of CuSO₄ : CuSO₄ \(\rightleftharpoons\) Cu²⁺ + SO₄^2-
(ii) n resolution of water : H₂O \(\rightleftharpoons\) H⁺ + OH^–
(iii) Reaction in cathode : Cu²⁺ + 2e → Cu^–
(iv) Reaction in anode : Cu – 2e → Cu²⁺

Conclusion : As a result of the electrolytic reaction describe above, anode is gradually dissoluted and due to deposition of copper in cathode it becomes thicker.

5. Electrolysis of aqueous solution of AgNO₃ :
(a) Using platinum electrodes:
Electrodes:
Cathode – Platinum

Anode – Platinum

Electrolyte : Aqueous solution of AgNO₃

Electrolytic reaction:
(i) Dissolution of AgNO₃ : AgNO₃ \(\rightleftharpoons\) Ag⁺ + NOg^–₃
(ii) Dissolution of water : H₂O \(\rightleftharpoons\) H⁺ + OH^–
(iii) Reaction in cathode : Ag⁺ + e → Ag
(iv) Reaction in anode : OH^– – e → OH; 4OH → 2H₂O + O₂↑

(b) Using silver electrodes :

Electrodes :
Cathode – Silver
Anode – Silver
Electrolyte : Aqueous solution of AgNO₃

Electrolytic reaction:
(i) Dissolution of AgNO₃ : AgNO₃ \(\rightleftharpoons\) Ag⁺ + NO^–₃
(ii) Dissolution of water : H₂O \(\rightleftharpoons\) H⁺ + OH^–
(iii) Reaction in cathode : Ag⁺ + e → Ag
(iv) Reaction in anode : Ag – e → Ag⁺

Practical application of electrolysis :

(i) Extraction of metal : Highly electro positive such as Na, Ca, Mg, Al etc. : metals are extracted by electrolysis method. e.g. Extraction of Aluminium (Al)

Electrolyte : It contains of pure alumina (Al₂O₃)-20% ;
Fused cryolite (Na₃A/F₆)-60% ; CaF₂-20%.

Electrolytic reaction:
(i) Decomposition of cryolite :
(Na₃AlF₆>) A1F₃ ; 3NaF \(\rightleftharpoons\)A1F₃+ 3NaF; A/F₃\(\rightleftharpoons\) Al³⁺ + 3F^–
(ii) Reaction in cathode : Al³⁺ + 3e → Al
(iii) Reaction in anode : 3F^– – 3e → 3F
(iv) Final reaction ; AF₂O₃ + 6F → 2A1F₃ + 3O ; 6O → 3O₂↑
Non-metals like oxygen, hydrogen, chlorine and industrial preparations of caustic soda (NaOH) and heavy water (D₂O) are done by electrolysis.

Electro-plating: Some metals are required to be electroplated because some­times for the preservation of the less active metal or article and to prevent rusting or for attractive appearance.

Electroplating of Cu, Ag. Ni, Sn, Cr, Zn, Au :

(iv) Metals after extraction by chemical means are purified by electrolysis, e.g. Purification of copper :

Electrolyte : In aqueous solution of copper sulphate, small amount of 1% H₂SO₄ is added to increase the conductivity of the solution.

Electrodes . Cathode : Pure thin copper plate Anode : Thick impure copper plate

Procedure : Electric current is now passed in the solution from a battery, copper ion is formed from anode and is mixed into the solution where in cathode copper metal is deposited.

Electrolytic reaction:

• Reaction in cathode : Cu²⁺ + 2e → Cu
• Reaction in anode : Cu – 2e → Cu²⁺

Conclusion : After passing electricity for sometimes it is found that anode, an impure copper metal is totally dissolved and a very thin plate of cathode gradually becomes thicker.

Ability to discharge ions in increasing order :

Comprehensive WBBSE Class 10 Physical Science Notes Chapter 5 Light can help students make connections between concepts.

Light Class 10 WBBSE Notes

Reflection of light: Light travelling in one medium when falls on a second medium, a portion of the incident light, depending on the nature of the surface of the second medium, is turned back into the first medium. This phenomenon is known as reflection of light.

Laws of reflection:

• The incident ray, the reflected ray and the normal at the point of incidence on the reflecting surface line in one plane.
• The angle of incidence is equal to the angle of reflection.

Real Image and Virtual image: If rays diverging from a point source after reflection or refraction suffer changes or direction and either actually converge to, or appear to diverge from a second point, the second point is called the image of the first point and the image is real in the first case and virtual in the second case.

Characteristics of the image formed by plane mirror

• the image is virtual
• the image is erect
• the size of the image is equal to the size of the object
• the image is formed as for behind the mirror as the object is infront of it
• the image is laterally inverted.

Effect of rotation of a plane mirror on the reflected ray: For a given incident ray, if a mirror be rotated through angle say θ, the reflected ray rotates through double the angle (2θ).

Multiple images formed by two mirrors inclined at an angle: When an object is kept between two mirrors inclined at an angle θ, a number of images are formed due to multiple reflections.

The number of images formed = \(\left(\frac{2 \pi}{\theta}-1\right)\)
when θ = 90°, images formed 3.
when θ = 0°, images formed infinite.

Spherical mirrors: A spherical mirror is a reflecting surface so curved that it forms a part of a regular hollow sphere.

Centre of Curvature: The centre of the sphere of which the mirror is a part is called the centre of curvature of the mirror. C and C’ are the centres of curvatures of a concave and a convex mirror respectively.

Radius of curvature: The radius of the sphere of which the mirror is a part called its radius of curvature (r).

Aperture: The perimeter of a spherical mirror is generally circular in shape and diameter (AB) of this circle is called aperture of the mirror.

Pole: The central point (P) of the mirror is called its pole.

Principal axis: The straight line (XX’) passing through the pole and centre of curvature is called principal axis of the mirror.

Principal section: When a spherical mirror is intersected by a plane passing through the principal axis, the section is a circular arc (APB) called principal section of the mirror.

Principal focus: A beam of rays parallel to the principal axis of a spherical mirror after reflection either converges to (in case of a concave mirror) or appears to diverge from (in the case of a convex mirror) a fixed point (F) on the axis, which is called the Principal focus of the mirror.

Focal length: The distance of the focus from the pole of the mirror is called the focal length (PF) of the mirror.

Focal plane: The plane passing through the principal focus of a mirror and at right angle to its principal axis is called the focal plane of the mirror.

Sign conventions:

As the radius of curvature and focal length of a concave mirror are measured towards the left of its pole, so they are taken as negative in the new cartesian sign convention.

As the radius of curvature and focal length of a convex mirror are measured towards the right of its pole, so they are taken as positive in this sign convention.

Relation between radius of curvature and focal length

r = 2f

The mirror formula: The general equation for a spherical mirror is

\(\frac{1}{u}+\frac{1}{v}=\frac{2}{r}=\frac{1}{f}\)

Linear magnification: The ratio of the linear size of the image to the linear size of the object is called the linear magnification.

m = \(\frac{h2}{h1}\) = \(\frac{-v}{u}\)

This relation is valid for both the mirrors (concave and convex).

In the case of a concave mirror depending on the position of the object, the image may be real, inverted, magnified, of same size or diminished and also virtual erect and magnified.

In the case of a convex mirror the image is always virtual, erect and diminished for all positions of the object.

The relation between the speed of object and fmage formed by a spherical mirror:

v_i = speed of image
v_o = speed of object

Applications of spherical mirrors:

• A concave mirror is used as a shaving mirror as it produces magnified erect image.
• A concave mirror is used as a reflector in search lights, head lights in cars, solar cookers etc.
• A concave mirror is used by the opticians in opthalmoscopes for reflecting light on the retina.
• A convex mirror is used as rear view mirrors, in automobiles as it always produces an erect image of diminished size giving a wide field of view.
• A convex mirror is used as a reflector in street lamps, as it can diverge light over a large area.

Refraction of light: The phenomenon of change in the direction of light ray, when it passes obliquely from one homogeneous medium to another is called refraction of light.

Laws of refraction:

The incident ray, the refracted ray and the normal at the point of incidence on the refracting surface lie in the same plane.

Snell’s Law: For a given pair of media and for a given colour of light, the sine of the angle of incidence bears a constant ratio to the sine of angle of refraction.

\(\frac{\sin t}{\sin r}\) = const = μ₂ (refractive index)

Types of refractive index :

Absolute refractive index: The refractive index of a medium with respect to vacuum or air is taken as the absolute refractive index of the medium.

Relative refractive index: The refractive index of a medium with respect to any other medium is called its relative refractive index.

Principle of Reversibility of Light: The principle states that if the path of ray of light is reversed after so suffering a number of reflections and refractions, it retraces its path. Thus according to this principle, image and object positions can be interchanged. The points corresponding to object and image are called conjugate points.

Generalised Snell’s law of refraction:

μ₁ sin i = μ₂ sin r

Optically denser media: When the absolute refractive index of a medium is greater then that of a second medium, then the first medium is called the optically denser media than the second one.

Optically rarer media: The second medium is called optically rarer media.

Real depth and Apparent depth:

When μ₁>μ₂, real depth > apparent depth i.e. when the observer is in rarer medium the image appears closer to the surface than the object.

When μ₂ = 1 i.e. when the observer in the air medium, μ₁= μ = refractive index of the medium in which object is situated then

μ = \(\frac{\text { real depth }}{\text { apparent depth }}\)

When μ₂>μ₁ i.e. when the observer in the denser medium, the image appears further away from the surface than the object.

For this reason a tank filled with water or any transparent liquid appears less deep. Also a straight stick put obliquely in water appears bent. lens is called double convex lens. It is used in camera, telescope etc.

Refraction through a parallel slab:

\({ }_1 \mu_2 \times{ }_2 \mu_1=1\)

Refraction through a compound slab:

\({ }_1 \mu_2 \times{ }_2 \mu_3={ }_1 \mu_3\)

Total internal reflection : It is a phenomenon in which a ray of light travelling from an optically denser medium to an optically rarer medium is incident at an angle greater than the critical angle for the pair of media in contact, the ray is totally reflected back into denser medium.

Conditions for total internal reflection :

• light must travel from a denser to a rerer medium.
• angle of incidence in the denser medium must be greater than the critical angle for the pair of media in contact.

Relation between refractive index and critical angle :

sin i_c = \(\frac{1}{μ}\)

Spherical refracting surface: A refracting surface, which is a part of a sphere of transparent refracting material is known as a spherical refracting surface.

Types of spherical refracting surfaces :

• convex spherical refracting surface: These surface have convex towards rarer medium side.
• Concave spherical refracting surface: These surfaces have towards rarer medium side.

Refraction from rarer to denser medium at a convex spherical refracting surface:

Image formation by a concave mirror:

Position of the object	Position of the image	Size of the image	Nature of the image
between	Behind the	Enlarged	virtual and erect
P and F	mirror	Highly enlarged	Real and inverted
A + F	A + infinity	Enlarged	Real and inverted
Between	Beyond C	Same size	Real and inverted
C and F	A + C	Diminished	Real and inverted
A + C	Between F and C	Highly dminished point sized	Real and inverted
Beyond C	At the focus F	Size of the image	Nature of the image
A + infinity	Position of the image	Enlarged	virtual and erect

Image formation by a convex mirror:

Position of the object	Position of the image	Size of the image	Nature of the image
At infinity	At the focus F, behind the mirror	Highly diminished point	virtual and erect
Between infinity and the pole P of the	Between P and F behind the mirror	sized	virtual and erect

The new cartesian sign convention for spherical mirrors :

Absolute Refractive index of some material media:

Lenses: A lens is a portion of a transparent medium bounded by two polished surfaces with at least one of them being curved.

Types of Lenses: Lenses are broadly of two types :

• Convex lens: If the lens is thicker at its centre than at its edges, it is a convex lens.
• Concave lens: The lens which is thinner of the centre and wider at the two edges is called a concave lens.

Other types of lenses:

Double convex lens : If both the surfaces of convex lens are convex then the lens is called double convex lens. It is used in camera, telescope etc.

Plano-convex lens: If one surface of convex lens is plane and the other is cinvex then it is called plano convex lens. It is used in eye piece of telescope.

Concavo-convex lens: If one surface of convex lens is convex and the other is concave then it is called concavo convex lens. It is used in spectacles.

Double-concave lens: It both the surfaces of concave lens are concave then the lens is called double concave lens.

Plano-concave lens: If one surface of concave lens is plane and the other is concave then if is called plano-concave lens.

Convexo-concave lens: If one surface of concave lens is concave and the other is convex then if is called convexo-concave lens.

Focal plane of lens: The plane passing through principal focus of a lens and perpendicular to the principal axis of the lens is known as the focal plane of the lens.

Centre of curvature: The spherical surface of a lens is a part of sphere. The centre of the sphere is known as centre of curvature of the surface of lens.

Principal axis of a convex lens: The line joining the centres of curvature of the two spherical surfaces of a convex lens is called its principal axis.

Redius of curvature: Radius of curvature of a lens is the radius of the glass sphere from which the surfaces of the lens are cut.

Focus of convex lens : It a beam of parallel rays, travelling parallel to the principal axis of a convex lens are refracted by the lens, the rays became converging and intersect each other at a particular point on the axis. The point is known as the focus of the convex lens.

Optical centre: It a ray of light strikes one surface of a lens in such a way that emergent ray from the other surface is parallel to it, then the corresponding, refracted ray passed through a definite point on the principal axis. The point is the optical centre of the lens.

Focal length: The distance between the optical centre and the focus is known as focal length.

Formation of image by a lens:

• A ray parallel to the principal axis would pass through the second focus in case of a convex lens or appear to diverge from the second focus in case of a concave lens.
• A ray passes through optical centre of the lens undeviated.
• A ray actually passing through the first focus in case of convex lens or appearing to diverge from the first focus in case of concave lens comes out of the lens parallel to the principal axis.

Location of images formed for both types of lenses in different cases:

Object placed in infinity, the image is real, inverted, diminished and formed at the focus in the focal plane (fig. 5.8)

In (fig 5.9) is shown the position of image formed by a convex lens due to an object between 2 f and the infinity. The image is formed in between f and 2 f and real, inverted and diminished.

The situation for an object at a distance of 2 f is shown in (fig 5.10). The image is real, inverted of equal is size to the object and formed at a distance of 2 f from the lens.

In (fig 5.11) is shown the position of the image formed by a convex lens when the object lies between 2 f and f. The image is real, inverted and magnified.

In (fig 5.12) is shown when the object is situated at the focus of the convex lens. The image is real, inverted, highly magnified and is situated at infinity.

In (fig 5.13) is shown when the object is situated at a position less than the focal length of the convex lens. The image is erect virtual and magnified.

It can be shown in the case of a concave lens image is always erect, diminished and virtual [fig(g).]. As the object from infinity towards the lens, the image moves from the focus towards the lens.

Human eye: Human eye can be treated as a natural optical camera. It is nearly spherical in shape having following principal parts.

• Cornea
• Iris
• Pupil
• Lens
• Retina
• Ciliary muscles
• Optic nerve.

Working of eye :

The working of eye is similar to that of a Camera. In eye the amount of light entering it is adjusted by the iris, like the shutter in camera. The size of the opening of the pupil is changed by ciliary muscles. In a camera focussing of image is done by moving the lens forward or backward, while in human eye its focal length is changed by changing its shape by muscular effort.

The eye lens which is a convex lens forms a real, inverted image on the retina of the eye. The retina contains cells of the shape of rods and cones, which convert light energy into electrical signals and carried to brain through optic nerves. These signals are interpreted by the brain and we are able to see the object.

Accomodation of eye : The process by which ciliary muscles change the focal length of the eye lens so that a sharp image of the object at any distance from the eye is formed on the retina is called accomodation of eye.

Range of normal eye : The range of a normal eye varies from 25 cm to infinity.

Near point : The nearest point from an eye at which an object can be placed to see its sharp image is near point. (25 cm).

Far point: The farthest point from an eye at which an object can be placed to see its sharp image is called far point. For a normal eye the far point is infinity from the eye.

Power of accomodation : For a normal eye, the power of accomodation is about 4D (dioptre).

Defects of vision and their corrections : The common defects of human eye are –

Myopia (short-sightedness) : The defect where far point is less than infinity is known as myopia.
For correction of a myopia eye a concave lens of focal length-d is to be used. The power p of the lens is given by \(\frac{100}{f(\mathrm{in} \mathrm{cm})}\) dioptre.

Hypermetropia.(Long-sightedness): The defect where the near point moves away from 25 cm, but the eye can see distant objects without difficulty is called hypermetropia.

The defect can be corrected by using a convex lens of suitable focal length. Power of the lens \(\frac{100}{f(\text { in } \mathrm{cm})}\) dioptre

Presbyopia : The defect where an eye cannot see the near objects as well as distant objects clearly is called presbyopia.
To correct this defect bifocal lens of proper power and type is used with the lower one a convex lens to correct the near point and upper one a concave lens to correct the far point.

Astigmatism : The defect where an eye cannot focus horizontal and vertical lines simultaneously is known as astigmatism.
The cause of this defect is that the cornea of the eye has different curvatures in different directions.
Astigmatism is corrected by using a cylin-drical lens of suitable radius of curvature and suitable axis.

Prism: A prism is a portion of a transparent medium bounded by at least two plane faces inclined at suitable angle to each other.

Refraction through a prism

Angle of the prism

A = r₁ + r₂

Deviation produced

D = i₁ + i₂ – A

Minimum deviation : It is seen that the angle of deviation depends upon –

• angle of incidence
• angle of the prism
• Nature of the material of the prism

Dispersion of light : The phenomenon of splitting of a beam of white light into its constitutent colours is called dispersion of light.

Spectrum : The band of different colours obtained due to dispersion of white lens is known as a spectrum.

Cauchy’s formula : D = (μ-1) A

A prism only splite up the colours already present in white light and does not produce the colours.
The splitting of colours takes place at the first refracting surface of the prism only. In the second surface it is further refracted.
As all colours travel in vacuum with same speed, the material of the prism has same m for all the colours and so no dispersion takes place in vacuum.
The dispersion phenomenon is not exhibited by sound waves in air.
Scattering of light : The process of radiating light by atoms and molecules of the medium in all directions is called scattering of light.

Lord Rayleigh’s equation :

a = \(\frac{A V}{r \lambda^2}\)

\(I_s \propto \frac{1}{\lambda 4}\)

(a = amplitude of scattered light at a distance r from the scattering particle in V volume. A = the amplitude of incident light of wave length λ.)

The intensity of scattered light varies inversely as the fourth power of the wavelength of the incident light-provided the size of the particles scattering light of very very small as compared to the wavelength of the incident light.

Some phenomena due to scattering of light

Blue colour of sky: \(I_s \propto \frac{1}{\lambda 4}\)

The intensity of the scattered blue light would be much more than that of the red colour. Thus in a clear sky, blue colour becomes prominent colour and the sky appears blue.

The clouds appear white

Reddish appearance of sun at sunrise and sunset.

Danger signals are red.

Pure spectrum: The spectrum in which the constituent coloums do not overlap an each other and are separated distinctly into elementary colours in known as a pure spectrum.

Impure spectrum: The spectrum in which the constituent colours partially superpose an each other and are not separated distinctly into elementary colours is known as impure spectrum.

Well structured WBBSE Class 10 Physical Science MCQ Questions Chapter 8.6 Organic Chemistry can serve as a valuable review tool before exams.

Organic Chemistry Class 10 WBBSE MCQ Questions

Question 1.
C_nH_{2n + 2} is general formula of ________
(A) Alkenes
(B) Alkynes
(C) Alkanes
(D) Ring
Answer:
(C) Alkanes

Question 2.
Aliphatic hydrocarbons with double bond : ________
(A) are saturated
(B) generally add bromine
(C) belong to the acetylene family group
(D) belong to the paraffin
Answer:
(B) generally add bromine

Question3.
When sodium acetate is heated with soda lime, the reaction is called: ________
(A) Dehydration
(B) Decarboxylation
(C) Dehydrogenation
(D) Dehydrohalogenation
Answer:
(B) Decarboxylation

Question 4.
Ethylene can be prepared by reacting ethyl bromide with : ________
(A) Alcoholic KOH
(B) Amoniacal AgNO₃
(C) Acidified KMnO₄
(D) C and H₂SO₄
Answer:
(A) Alcoholic KOH

Question 5.
The product obtained when chloroform is treated with silver powder is: ________
Ethylene
ethane
Acetylene
Methane
Answer:
Acetylene

Question 6.
A metallic carbide on treatment with water gives a colourless gas which burns readily in air and gives a precipitate with ammoniacal silver nitrate. The gas is : ________
(A) Methane
(B) Ethane
(C) Ethylene
(D) Acetylene
Answer:
(D) Acetylene

Question 7.
A gas decolourises bromine in CCl₂ and forms a precipitate with ammoniacal silver nitrate. The gas is :
(A) Acetylene
(B) Ethylene
(C) Methane
(D) Ethane
Answer:
(B) Ethylene

Question 8.
The LHCC bond angle in ethylene is : ________
(A) 90°
(B) 120°
(C) 109° 28’
(D) 180°
Answer:
(B) 120°

Question 9.
Saturated hydrocarbons mainly undergo : ________
(A) Addition reactions
(B) Substitution reactions
(C) Elimination reaction
(D) Polymerisation
Answer:
(B) Substitution reactions

Question 10
Which of the following bonds is strongest?

Answer:
(C)

Question 11.
The reaction
is called : ________
(A) Kolbe’s reaction
(B) Annizzaro’s reaction
(C) Sabatier and Senderen’s reaction
(D) Clemmensen reaction
Answer:
(C) Sabatier and senderen’s reaction

Question 12.
Both methane and ethane may be obtained in one step reaction from ________
(A) C₂H₄
(B) CH₃I
(C) CH₃OH
(D) C₂H₅OH
Answer:
(B) CH₃I

Question 13.
Which of the following liberates methane on treatment with water ?
(A) Silicon carbide
(B) Calcium carbide
(C) Aluminium carbide
(D) Iron carbide
Answer:
(C) Aluminium carbide

Question 14.
On heating sodium acetate with sodium hydroxide, the gas evolved will be : ________
(A) Acetylene
(B) Ethane
(C) Methane
(D) Ethylene
Answer:
(C) Methane

Question 15.
A compound having a triple bond is more reactive because : ________
(A) there is a strain in the molecule
(B) valency of hydrogen is different
(C) electron density is higher
(D) none
Answer:
(C) electron density is higher.

Question 16.
Acidic hydrogen is present in : ________
(A) Ethyne
(B) Ehene
(C) Benzene
(D) Ethane
Answer:
(A) Ethyne

Question 17.
Final product of the oxidation of hydrocarbon is : ________
(A) CO₂ and H₂O
(B) Alcohol
(C) Acid
(D) Aldehyde
Answer:
(A) CO₂ and H₂O

Question 18.
General formula for alkenes is : ________
(A) C_nH_2n
(B) C_nH_2n+1
(C) C_nH_2n-1
(D) C_2nH_2n
Answer:
(A) C_nH_2n

Question 19.
Marsh gas mainly contains : ________
(A) H₂S
(B) CO
(C) CH₄
(D) C₂H₂
Answer:
(C) CH₄

Question 20.
Which of the following gases is used in welding ?
(A) C₂H₄
(B) C₂H₂
(C) CH₄
(D) C₂H₆
Answer:
(B) C₂H₂

Question 21.
Which hydrocarbon is used in making printer’s ink and paints ?
(A) CH₄
(B) C₂H₆
(C)  C₂H₄
(D)  C₂H₂
Answer:
(A) CH₄

Question 22.
The sugar which is stored in the liver to act as reserve food is : ________
(A) Glycogen
(B) Glucose
(C) Sucrose
(D) Fructose
Answer:
(A) Glycogen

Question 23.
Sweetest among all the sugar is : ________
(A) Fructose
(B) Glucose
(C) Sucrose
(D) Lactose
Answer:
(A) Fructose

Question 24.
The main structural feature of protein is : ________
(A) Ether linkage
(B) Peptide linkage
(C) Ester linkage
(D) All the above
Answer:
(B) Peptide linkage

Question 25.
Which of the following is protein ?
(A) Terry cotton
(B) Natural silk
(C) Nylon
(D) Rayon
Answer:
(B) Natural silk.

Question 26.
Which of the following contains nitrogen ?
(A) Fats
(B) Proteins
(C) Carbohydrate
(D) None
Answer:
(B) Proteins

Question 27.
Which of the following is an organic compound ?
(A) urea
(B) NaHCO₃
(C) CO₄
(D) NH₄ CNS
Answer:
(A) urea

Question 28.
Organic compound are:________
(A) high melting
(B) low meffing
(C) soluble in water
(D) conducts electricity in molten state
Answer:
(B) low melting

Question 29.
Tetravalence of carbon is proposed by: ________
(A) Wohler
(B) Lavoisier
(C) Kekule
(D) Vant Hoff
Answer:
(C) Kekule

Question 30.
Tetrahedral model of carbon compounds proposed by: ________
(A) Kekule
(B) Rutherford
(C) Wohier
(D) Vant Hoff
Answer:
(D) Vont Hoff

Question 31.
The number of covalent bonds present in ethane is : ________
(A) 4
(B) 6
(C) 7
(D) 9
Answer:
(C) 7

Question 32.
Which molecule has tetrahedral geometry? ________
(A) methane
(B) ethylene
(C) acetylene
(D) carbon dioxide
Answer:
(A) methane

Question 33.
Which does not react with metallic sodium?
(A) methyl alcohol
(B) ethyl alcohol
(C) acetic acid
(D) dimethyl ether
Answer:
(D) Dmethyt ether

Question 34.
How many positional isomers are possible with the molecular formula C₃H₁₀?
(A) 1
(B) 2
(C) 3
(D) 4
Answer:
(C) 2

Question 35.
How many functional isomers are possible with molecular formula C₃H₈O?
(A) 1
(B) 3
(C) 2
(D) 4
Answer:
(C) 2

Question 36.
IUPAC name of CH₃ CH₂ CH₂ OH is:
(A) propan-1-oI
(B) n-propanol
(C) isopropanol
(D) propyl alcohol
Answer:
(A) Propon-I-ol

Question 37.
IUPAC name of Formaldehyde Is:
(A) Butanal
(B) Propanal
(C) Ethanal
(D) Methanal
Answer:
(D) Methanal

Question 38.
The total number of different carbon chains that five carbon atoms form in alkane is:
(A) 5
(B) 4
(C) 3
(D) 2
Answer:
(C) 3

Question 39.
The IUPAC name of the hydrocarbon present in rectified spirit is :
(A) methanol
(B) ethanol
(C) trichioromethane
(D) ethanai
Answer:
(B) ethanol

Question 40.
Which of the following functional group is present in vinegar?
(A) -CHO
(B) C=O
(C) -COOH
(D) -OH
Answer:
(C) -COOH

Question 41.
Which of the following can damage optic nerve?
(A) acetic acid
(B) ethyl alcohol
(C) acetone
(D) methanol
Answer:
(D) methanol

Question 42.
Which one of the following is not a polymer?
(A) LPG
(B) Jute
(C) PVC
(D) PET
Answer:
(A) LPG

Question 43.
Urea was synthesized by wohier from ………
(A) ammonia and carbon monoxide
(B) ammonium cyanate
(C) ammonium thiocyanate
(D) ammonium chloride and CO₂
Answer:
(B) ammonium cyanate

Question 44.
Identify the wrong statement
(A) Organic compounds have low m.p. and b.p.
(B) Organic Compounds are Soluble in solvent having high dielectric constant.
(C) Most organic compounds are do not conduct electricity
(D) Most of the organic compounds are liquid or gaseous under ordinary temperature and pressure.
Answer:
(b) Organic Compounds are soluble in solvent having high dielectric constant.

Question 45.
Organic compounds are generally
(A) Soluble in water
(B) insoluble in water
(C) ionize in water
(D) hydrolyze in water
Answer:
(B) insoluble in water

Question 46.
The biggest source of methane is …………….
(A) Synthesis gas
(B) natural gas
(C) nerve gas
(D) LPG
Answer:
(B) natural gas

Question 47.
Chlorine reacts with saturated hydrocarbons at room temperature in the
(A) presence of sunlight
(B) absence of sunlight
(C) presence of moisture
(D) presence of an acid catalyst
Answer:
(A) presence of sunlight

Fill in the Blanks:

1. …………. is the abbreviation of polyvinyl chloride.
Answer:
PVC.

2. The monomer of …………. is tetrafluoroethene.
Answer:
teflon.

3. …………. is a large molecule made up of many similar units of small molecules.
Answer:
Polymer.

4. The compound bearing the monovalent functional group – CHO are ………….
Answer:
aldehydes.

5. Alkynes are hydrocarbons where at least two carbon atoms combine with a …………. bond.
Answer:
triple.

6. The function group of organic acid is ………….
Answer:
– COOH

7. The functional group of …………. is -NH.
Answer:
amines.

8. Hydrocarbons in which at least two carbon atoms join with a double bond are called ………….
Answer:
alkenes.

9. Catenation is the property where a large number of …………. atoms link together to form large organic molecules.
Answer:
carbon.

10. Proteins contain various kinds of …………. acids.
Answer:
amino

11. RNA is the abbreviation for…………. acid.
Answer:
ribonucleic.

12. …………. is a complex organic compound responsible for reproduction and maintaining heredity.
Answer:
Gene.

13. …………. and proteins are the polymerisation products of amino acids.
Answer:
Polypeptides.

14. Amino acids are the end products of the digestion of ………….
Answer:
proteins.

15. Polypeptide chains are the chains of ………….
Answer:
polymers of amino acids.

16. Sucrose on hydrolysis give one …………. and one fructose molecule.
Answer:
glucose.

17. Starch is …………. saccharide.
Answer:
poly.

18. Carbohydrates containing a keto group are called ………….
Answer:
ketoses.

19. Vitamin C is soluble in ………….
Answer:
water.

20. Globular proteins me …………. in water.
Answer:
soluble.

21. The carbon chains in alkenes are ………….
Answer: zig-zag.

22. Hydrocarbons are more soluble in …………. solvents.
Answer:
non-polar.

23. Ethane on combustion produces ………….
Answer:
Carbon dioxide and water.

24. AlC evolves …………. when treated with water.
Answer:
methane.

25. Halogenation of alkanes does not occur in ………………….
Answer: dark.

26. Wurtz reaction is used for the preparation of ………………….
Answer:
alkanes.

27. Melting point of organic compounds are …………………. than of inorganiccompounds.
Answer:
lower.

28. Organic compounds are …………………. and inorganic compounds are…………………..
Answer:
covalent, electrovalent

29. Kekule proposed C is …………………. and Vant Hoff proves C is ………………….
Answer:
tetravalent, covalent

30. The simplest alkane is …………………..
Answer:
methane

31………………… is the active ingredient of all alcoholic drinks.
Answer:
Ethanol

32. The first organic compound synthesized in the laboratory is ……..
Answer:
urea

33. H – C – H bond angle is methane is …………….
Answer:
109°28′

34. The existence of huge number of carbon compounds are due to two properties of carbon : tetravalency and ……………
Answer: catenation

35. n-propyl alcohol and iso-propyl alcohol exhibit…………… isomerism.
Answer:
positional

36. Methane, ethane and propane are the first three members of a ………….. series.
Answer:
homologous

37. …………. is the main constituent of CNG.
Answer:
Methane

38. Ethanoic acid is commonly known as…………..acid.
Answer:
acetic

39. IUPAC name of formic acid is …………
Answer:
methanoic acid

State whether the following statement is True or False : VSA

1. One must not drive a car after consuming alcohol._________________
Answer:
True

2. Denatured spirit cannot be consumed orally._____________________
Answer:
True

3. ‘Carbon’ comes from the Latin word ‘carbo’ meaning coal.
Answer:
True

4. Methane is the main constituent of marsh gas.
Answer:
True

5. Industrially ethane is produced by catalytic cracking of petroleum.
Answer:
True

6. Burning of methane in air is an exothermic reaction.
Answer:
True

7. PVC is highly fire resistant,
Answer:
True

8. Ethanol is used as a solvent in laboratory.
Answer:
True

9. Ethanol damages the optic nerve and may cause blindness.
Answer:
False

10. Teflon is hydrophobic and high heat resistant.
Answer:
True