WBBSE Class 10 Physical Science Solutions Chapter 8.3 Electricity and Chemical Reactions

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.