WBBSE Class 9 Physical Science Solutions Chapter 4.3 Solution

Detailed explanations in West Bengal Board Class 9 Physical Science Book Solutions Chapter 4.3 Solution offer valuable context and analysis.

WBBSE Class 9 Physical Science Chapter 4.3 Question Answer – Solution

Very short answer type questions

Question 1.
Write down the name of an inorganic and an organic solvent.
Answer:
Name of an inorganic solvent: water Name of an organic solvent: benzene

Question 2.
Write down the name of a substance whose solubility remains almost the same with rise of temperature.
Answer:
Solubility remains almost the same with rise of temperature: Sodium chloride (NaCl).

Question 3.
Write down the name of a substance whose solubility decreases with the increase of temperature.
Answer:
Solubility decreases with the increase of temperature: Calcium sulphate (CaSO₄).

Question 4.
Write down the name of a substance whose solubility increases tremendously with the increase of temperature.
Answer:
Solubility increases tremendously with the increase of temperature: e.g. Potassium nitrate (KNO₃)

Question 5.
What is the unit of solubility ?
Answer:
Solubility has no unit.

Question 6.
Which gas is soluble in soda water ?
Answer:
Carbon dioxide (CO₂) is soluble in soda water.

Question 7.
Give an example of a drying agent.
Answer:
Drying agent : concentrated H₂SO₄.

Question 8.
Give a common example of colloidal solution.
Answer:
Common example of colloidal solution : milk.

Question 9.
What are the components of a colloidal solution ?
Answer:
Components of a colloidal solution :

• dispersed phase
• dispersion medium

Question 10.
Give one example of a salt having water of crystallisation.
Answer:
Example of a salt having water of crystallisation :
Blue vitriol (CuSO₄. 5H₂O)

Question 11.
Mention one particulate matter in air that causes its pollution.
Answer:
Particulate matter in air that causes its pollution : Fine particules of dust.

Question 12.
What are the sizes of the colloid particles?
Answer:
Sizes of the colloid particles : 10^-5 cm to 10^-7 cm in diameter.

Question 13.
State whether solution is a mixture or compound.
Answer:
Solution is a mixture.

Question 14.
Why edible salt (NaCl) becomes moist in the rainy season?
Answer:
Edible salt (NaCl) becomes moist in rainy season due to the presence of deliquescent MgCL₂ 6H₂O as impurity in it.

Question 15.
Name an efflorescent substance.
Answer:
Efflorescent substance: Washing soda (Na₂CO₃.10H₂O)

Question 16.
Name a deliquescent substance.
Answer:
Deliquescent substance : Calcium chloride (CaCl₂)

Question 17.
What happens if a saturated solution is cooled?
Answer:
The cooled solution sheds the excess solute as crystals.

Question 18.
What is the effect of increase of pressure on the solublilty of a gas In water?
Answer:
Increase of pressure increases solubility of a gas.

Question 19.
What is the effect of increase of pressure on the sotubility of a solid in water?
Answer:
Increase of pressure does not cause any change of solubility of a solid in water.

Question 20.
What is occlusion?
Answer:
Hydrogen get dissolved in spongy palladium in some similar metals. This phenomenon is called occlusion.

Question 21.
What is TEL?
Answer:
Tetra ethyl lead (TEL).

Question 22.
What is epsome salt?
Answer:
Epsome salt : MgSO₄, 7H₂O

Question 23.
What is SPM?
Answer:
Suspended particulate matter (SPM)

Question 24.
What do you mean by smog ?
Answer:
Smog is fog containing smoke.

Question 25.
How a saturated solution may be made unsaturated ?
Answer:
A saturated solution may be made unsaturated either by :

• adding more solvent
• or, raising temperature of the solution.

Question 26.
State the biological importance of dissolved O₂ in water.
Answer:
Aquatic plants and animals can take oxygen for their respiration.

Question 27.
What is the effect of temperature on the solubility of KNO₃ and CasO₄ ?
Answer:
Solubility of KNO₃ increases with rise of temperature.
Solubility of CaSO₄ decreases with rise of temperature.

Question 28.
How can you increases the solubility of a given volume of gas in water ?
Answer:
An increase of pressure on the surface of water causes increase of solubility of gas in water.

Question 29.
Why does the CO₂ gas rapidly bubbles out when the lid of its bottle is opened ?
Answer:
CO₂ gas rapidly bubbles out when the lid of its bottle is opened because on opening the lid the pressure on the solution suddenly decreases.

Question 30.
Which solution is more concentrated : 10g/L NaOh or 10 molar NaOH solution ?
Answer:
10 molar NaOH solution.

Short Answer Type Question

Question 1.
What is a solution ?
Answer:
Solution : A solution (or true solution) is a uniformly homogeneous mixture of two or more substances whose relative proportions may be varied upon a certain limit.

Question 2.
Name the different types of solution known to you in respect of concentration.
Answer:
Classification of solution : Solutions are classified into three types based on concentration at a certain temperature. These are :

•  unsaturated
• saturated
• super saturated solutions.

Question 3.
What is an unsaturated solution ?
Answer:
Unsaturated solution : At a particular temperature, an unsaturated solution is one in which the solvent is capable of dissolving further amount of the solute.

Question 4.
What is a saturated solution ?
Answer:
Saturated solution : A saturated solution at a particular temperature is one in which the amount of the solvent has reached its maximum capacity of dissolving the solute.

Question 5.
What is a supersaturated solution ?
Answer:
Supersaturated solution : A supersaturated solution is one, in which the amount of the solvent has dissolved more amount of the solute than is necessary to make a saturated solution at the particular temperature.

Question 6.
How can you detect a saturated sugar solution ?
Answer:
Detection for saturated sugar solution : To the given solution, some amount of sugar is added into the solution and stirred. If the added sugar does not dissolve, the solution is said to be a saturated solution at that temperature.

Question 7.
How can you detect an unsaturated sugar solution ?
Answer:
Detection for unsaturated sugar solution : To the tested solution some sugar is added and stirred. If the sugar readily dissolves, the given solution is said to be an unsaturated solution.

Question 8.
What do you mean by solute ?
Answer:
Solute : The substances which are present in smaller quantities and gets dissolved are called solute.

Question 9.
What is meant by solvent ?
Answer:
Solvent : The medium in which the solutes are uniformly dispersed through dissolution is called the solvent.

Question 10.
Define a colloid or colloidal solution.
Answer:
Colloid or colloidal solution : A colloid or colloidal solution is a stable heterogeneous solution consisting of finely divided particles of a substance (of the size of 10^-5 cm to 10^-7 cm in diameter) uniformly dispersed in a continuous medium.

Question 11.
What do you mean by solubility ?
Answer:
Solubility : Solubility of a given solute in a solvent is defined as the weight in grams of the solute dissolved in 100 grams of solvent so as to saturate the solution at a given temperature.

Question 12.
What is meant by ‘solubility is dependent on temperature’ ?
Answer:
Solubility is dependent on temperature: It means, in general, solubility of a solid in a liquid solvent increases with increasing temperature and decreases with decreasing temperature. This rule is not obeyed in some cases.

Question 13.
What are the effects of temperature on solubility of CaSO₄) KNO₄, NaCl ?
Answer:
Effect of temperature on solubility of CaSO₄, KNO₃, NaCl.
Solubility of CaSO₄ decreases with increasing temperature.
Solubility of KNO₃ increases rapidly with rise of temperature.
Solubility of NaCl remains almost unchanged with rise of temperature

Question 14.
What do you mean by ‘dispersed phase’ and ‘dispersion medium’ ?
Answer:

• Dispersed phase : The component of colloid present in small amount and which behaves like a solute in a solution is called dispersed phase.
• Dispersion medium : The component of colloid present in excess amount and which behaves like a solvent in solution is called dispersion medium.

Question 15.
Define crystal.
Answer:
Crystal : Crystals are homogeneous solid particles bounded by plane surfaces arranged symmetrically and meeting at sharp edges and forms a definite three-dimenstional geometrical shape.

Question 16.
What do you mean by crystallisation ?
Answer:
Crystallisation : Crystallisation is a process by which crystals of a substance are obtained from its solution.

Question 17.
What is water of crystallisation ?
Answer:
Water of crystallisation : The fixed number of water molecules that are associated with a crystal as an integral part of the constitution of the crystal is called water of crystallisation.
Example : Blue vitriol (CuSO₄, 5H₂O) has five molecules of water of crystallisation.

Question 18.
What is meant by efflorescent substance ?
Answer:
Efflorescent substance : Efflorescent substances are those which crumble to powder when exposed to air due to partial or total loss of water molecules present in their crystalline structures.
Example : Washing soda (Na₂CO₃, 10H₂O)

Question 19.
What do you mean by deliquescent substance ?
Answer:
Deliquescent substance : Deliquescent substances are those solid which when exposed to atmosphere form concentrated solution dissolving in the moisture absorbed by them from air.
Example : Calcium chloride (CaCl₂).

Question 20.
What happens if a saturated solution is cooled ?
Answer:
If a hot saturated solution is cooled, the capacity of holding solute by the solution decreases. The cooled solution sheds the excess solute as crystals.

Question 21.
What are the effects of increase of pressure on the solubility of a gas and a solid solute in water ?
Answer:
Increase of pressure increases solubility of a gas in water ; increase of pressure does not cause any change of solubility of a solid in water.

Question 22.
Why is temperature mentioned in defining solubility ?
Answer:
In defining solubility of a substance, temperature is to be mentioned, because, with change of temperature solubility of most of the substances changes.

Question 23.
Why is a solution kept stirred continuously during its preparation ?
Answer:
It is done to mix well the saturated and the unsaturated portions of the solution to bring about homogeneity of the solution.

Question 24.
What are hygroscopic substances ?
Answer:
Hygroscopic substances : Certain substances exposed to air absorb moisture from air but are not dissolved in the absorbed water. These substances are called hygroscopic substances.

Question 25.
What are drying agents ?
Answer:
Drying agents : Some substances have the property to absorb moisture from moisturous bodies present nearby. These substances are called drying agents.
Example : Concentrated H₂SO₄, Phosphorous pentoxide (P₂O₅), Silica gel.

Question 26.
What is Mother liquor ?
Answer:
Mother liquor : In the process of crystalisation, the saturated solution left after separation of crystals is known as Mother liquor.

Question 27.
Define unit of concentration of solution in percentage.
Answer:
Concentration of solution in percentage :
If V ml of the solution contains W g of the solute, percentage of the solution is \(\frac{W}{V}\) × 100%

Question 28.
Define unit of concentration of solution in grams per litre.
Answer:
Concentration of solution in grams per litre :
Its unit is g/L. When 1 litre (1000 ml) of the solution, contains w grams of the solute, its strength is w g/1L.

Broad answer type questions 

Question 1.
‘Solubility of A of t°C is y’ — what does it mean ?
Answer:
‘Solubility of A at t°C is y’ — it means y’ g of A can produce a saturated solution when dissolved in a solvent at t°C.

Question 2.
How can you transform a saturated solution into an unsaturated one without adding more solvent ?
Answer:
Without adding more solvent a saturated solution may be made unsaturated by raising its temperature at which the solubility of the solute increases appreciably and the solution thus turns unsaturated.

Question 3.
How does solubility of KNO₃, NaCl and CaSO₄ change with rise of temperature ?
Answer:
Solubility of KNO_t increases rapidly with rise of temperature.
Solubility of NaCl remains almost unchanged with rise of temperature.
Solubility of CaSO₄ decreases with increasing temperature.

Question 4.
What is the cause of efflorescence ? Give one example of efflorescent substance.
Answer:
Cause of efflorescence : Efflorescence happens only when the vapour pressure within the hydrated crystal at ordinary temperature is greater than the vapour pressure of the atmosphere. These hydrated crystals are called efflorescent substances.
Example : Na₂CO₃, 10H₂O

Question 5.
What is the cause of deliquescence ? Give one example of deliquescent substance.
Answer:
Cause of deliquescnces : Deliquenscence occurs when the vapour pressure of water in the deliquescent substance is less than the vapour pressure in the atmosphere at ordinary temperature.
Example : CaCl₂

Question 6.
Why does effervescence occur when a soda water bottle is opened ?
Answer:
Soda water is a solution of carbon dioxide in water, prepared under high pressure. For this reason when a bottle of soda water is opened, i.e. pressure on the liquid content in the bottle is reduced, effervescence or raising bubbles occur. These effervescences form, as a part of dissolved carbon dioxide gas, escapes through the liquid.

Question 7.
Why edible salt becomes moist in rainy season ?
Answer:
Edible salt (NaCl) becomes moist in rainy season due to the presence of deliquescent substances like MgCl₂ and CaCl₂ as impurities in it.

Question 8.
How can you prepare a super saturated solution of a solid solute (hypo) at room temperature ?
Answer:
Preparation of a super saturated solution : Super saturated solution can be prepared by heating a few crystals of sodium thiosulphate or hypo (Na₂S₂O₃, 5H₂O) in a test tube. The crystals appear to melt or they dissolve in their own water of crystallization and a very concentrated solution of the salt in water is obtained.

The test tube is plugged with cotton wool and allowed to cool to the room temperature. This solution is super saturated and even after cooling, no excess solute separates out. If a crystal of the salt is now added into this solution, the crystal groups in size and the whole liquid begins to solidify with evolution of heat.

Question 9.
Why does clear lime water turn milky when heated ?
Answer:
Clear lime water turns milky when heated : Since solubility of slaked lime [Ca(OH)₂] decreases with increase of temperature, clear lime water which is an aqueous solution of Ca(OH)₂ or slaked lime turns milky when heated.
Reason : Due to decrease of solubility at a higher temperature, the excess undissolved slaked lime remains in suspension for which the solution appears milky.

Question 10.
Briefly describe the process of crystallisation.
Answer:
Crystallisation : Crystallisation is a process from which crystal of a substance is obtained from its solution. Process of crystallisation for the preparation of crystal :

(a) From saturated solution of a substance : A hot saturated solution of the substance is slowly cooled and then the crystal of that substance is obtained.

(b) From unsaturated solution : An unsaturated solution is vapourised and thus a concentrated solution of it is obtained. Now if this solution is gradually cooled then crystals of the substance are obtained.

(c) Sublimation process : Iodine, camphor etc. are sublimed. If the sublimate so formed is cooled, then the crystals of the substances are deposited in the pot.

(d) From molten matter : Solid sulphur taken in a pot is heated to melt it and then by slowly cooling, the crystals of P-sulphurs are obtained.

Question 11.
What is colloid ? How does it differ from a true and a suspension state ?
Answer:
Colloid : A colloid is a stable heterogenous solution consisting of finely divided particles of a substance (of the size of 10^-5 cm to 10^-7 cm in diameter) uniformly dispersed in a continuous medium. The component of colloid present in small amount and it behaves like a solute in a solution which is called dispersed phase. The component of colloid present in excess amount and which behaves like a solvent in a solution is called dispersion medium.

Identification of true solution, colloid and suspension : True solution, colloid and suspension are identified on the basis of particle size in it Size of a particle in colloidal state is 10^-5 cm to 10^-7 cm in diameter. The particle in true solution is 10^-8 cm in diameter. The particle in suspension state is
10^-8 cm in diameter.

Question 12.
How can an unsaturated solution be converted to saturated state without adding more solute ?
Answer:
(i) Without adding more solute an unsaturated solution may be made saturated by evaporating off a part of the solvent when the remaining lesser quantity of solvent becomes saturated with the initial content of solute.

(ii) Also, by lowering the temperature of the given solution, it may be made saturated since the solute present in the solution may make it saturated at a lower temperature, because solubility of a substance in general decreases with lowering of temperature.

Question 13.
Describe briefly the mechanism of formation of a solution where a solid dissolves in a liquid.
Answer:
Mechanism of formation of solution of a solid in the liquid : When a solid solute comes in contact with a liquid solvent, the tiny solid particles of diameter 10^-8 cm or less leave the surface of the solid solute depending on temperature and as concentration of the solution increases, some solid particles return and get deposited on the surface of the lump of solute.

At the initial stage, the rate of leaving the solute surface increases and it slows down when concentration of the solution increases. If the rate of leaving the surface of solute is greater than that of their return, the solid dissolves totally.

Question 14.
Why does the colour of sky appear to be blue ?
Answer:
Colour of sky appears to be blue due to the scattering of blue light by dust particles along with water suspended in air.

Question 15.
What is fire foam ?
Answer:
Fire foam : Carbon dioxide froth made by mixing solution of sodium bicarbonate and alum is called fire foam. It is used in fire extinguishers. A protective colloid such as glue or dextrin is added to stabilise the foam.

Question 16.
Does formation of a solution accompany heat exchange ?
Answer:
There is almost always heat changes accompanying formation of solutions. This means some solutes, when go into solution, heat is evolved and for some other solutes heat is absorbed.
e.g.

• NH₄Cl, KNO₃ etc. absorbs heat while they go into the solution i.e. the change is endothermic occurs, so their solubility increases with rise of temperature.
• Solubility of sodium chloride remains almost unchanged with rise of temperature.
• Heat evolves when calcium hydroxide, anhydrous sodium sulphate etc. go into solution. The change in such cases is exothermic, so solubility of them decreases with rise of temperature.