SEPARATION OF SUBSTANCES ( By: Dharmendra Sir )

(A) VERY SHORT ANSWER QUESTIONS:

Q. 1-By what name are the substances present in a mixture called?

Ans-Constituents or mixtures

Q. 2-Give one example of heterogeneous mixture.

Ans-Chalk in water

Q. 3-What happens when vapour of a liquid is cooled?

Ans-It gets condensed and converts into water.

Q. 4-Do oil and water form a homogeneous mixture?

Ans-No, they form a heterogeneous mixture.

Q. 5-Name the term that describes the maximum mass of a solute that can be dissolved in 100 g of the solvent.

Ans-Solubility

(B) SHORT-ANSWER QUESTIONS:

Q. 1-Describe the process called loading.

Ans-During sedimentation, the finer particles can be made to settle faster by dissolving a small quantity of alum in muddy water. This method is called loading.

Q. 2-How much solid solute can be dissolved in certain fixed quantity of a solvent?

Ans-It depends on its solubility.

Q. 3-Name the methods employed during the purification of an impure sample of common salt.

Ans-The following processes are employed-

         Dissolution, filtration and evaporation.

Q. 4-Why do fish in shallow pond die during summers?

Ans-The fish in shallow pond die during summers because the water in the pond gets warm due to summer heat. As a result, the amount of dissolved oxygen in water decreases and the fish in that pond die.

Q. 5-What is meant by aqueous solution? How does the solubility of a solid change with rise in temperature?

Ans-Solution of any substance in water is known as its aqueous solution. Solubility of a solid rise increases with the rise in temperature.

(C) LONG ANSWER QUESTIONS:

Q. 1-Define heterogeneous and homogeneous mixture. Give one example of each.

Ans-Mixtures in which particles of the substances present can be seen are called heterogeneous mixtures. For example- dust in air.

Mixtures in which the particles of the substances present cannot be seen are called homogeneous mixtures. For example-solution of sugar and salt in water.

Q. 2-Describe sedimentation and decantation. What kind of mixtures can be separated by decantation?

Ans-

Sedimentation-Separating the suspended particles of a solid from the liquid using the effect of gravity is called sedimentation.

Decantation- Separating clear liquid without disturbing the settled solid particles simply by transferring.

Solid coarse particles which are insoluble in the liquid can be separated by decantation.

Q. 3-What is meant by a pair of miscible liquids? Give one example of such a pair.

Ans-The two liquids which dissolve in one another are called a pair of miscible liquids. For example-lemon juice and water.

Q. 4-Draw a flowsheet diagram describing separation of the constituents of a mixture containing sand and common salt.

Ans-

Q. 5-Define solubility of a solid substance in water. How does the solubility of common salt in water change with a rise in temperature?

Ans-The maximum mass of a solute that can be dissolved in 100 g of the solvent at any specified temperature is called its solubility. The solubility of common salt in water increases with a rise in temperature.

(D) TICK THE ODD ONE-ONE OUT GIVING REASON

Q. 1-Dust in air, Solution of salt in water, Cold drinks, Air (pure)

Ans-Dust in air because it is a heterogeneous mixture and rest others are homogeneous mixtures.

Q. 2-Sedimentation, Evaporation, Condensation, Dissolution

Ans-

3-Filtrate, Filter paper, Residue, Sugar solution, Suspension

Ans-Sugar solution because rest others are part of filtration method.

Q. 4-Soluble, Aqueous solution, Homogeneous, Heterogeneous

Ans-Heterogeneous because rest others are related to homogeneous mixtures.

Q. 5-Homogeneous mixture, Pure substance, Heterogeneous mixture

Ans-Pure substance because rest others are mixtures.

(E) DEFINE THE FOLLOWING TERMS

1-Components of a mixture-the various substances present in a mixture are called its components or constituents.

2-Threshing-The process of separating grains from sun dried stalks is called threshing.

3-Loading-During sedimentation, the finer particles can be made to settle faster by dissolving a small quantity of alum in muddy water. This method is called loading.

4-Saturated solution-A solution in which no more solute can be dissolved at a given temperature is called a saturated solution.

5-Solubility- The maximum mass of a solute that can be dissolved in 100 g of the solvent at any specified temperature is called its solubility.

HOTS ( HIGHER ORDER THINKING SKILLS )

Q. 1-A sample water boils at 102*C and has salty taste. What do you conclude from this?

Ans-1 conclude from this that the given sample of water contains some impurities(salt) because the boiling point of pure water is 100°C.

Q. 2-You are given sample of a white powdery substance. It may be common salt or chalk powder. How will you identify it without tasting it?

Ans-I will dissolve that sample in the water. If it is common salt, it will be dissolved in the water and makes homogeneous mixture. If it is chalk powder, it will not be dissolved in the water and makes a heterogeneous mixture.

Q. 3-During the purification of water for city supply, the raw water from the river /lake is allowed to stand undisturbed in large tanks. What happens here?

Ans-The process sedimentation happens here so that solid insoluble impurities settle down at the bottom of the tank.