CLASS XII: ASSIGNMENT ON SOLUTIONS

SOLUTIONS

 

1 Mark Questions

1 How does the morality of a solution change with temperature?

2 What is the sum of the mole fractions of all the components in a three component system?

3 What temperature change is expected during the mixing of two liquids whose solution shows a negative deviation from Raoult’s law ?

4 What are interstitial solid solutions? Give an example.

5 What type of azeotrope is formed on mixing nitric acid and water?

2 Marks Questions

6 With the help of a suitable diagram, show that the lower vapour pressure of a solution than the pure solvent, causes a lowering of freezing point for the solution compared to that of pure solvent.

7 Concentrated nitric acid used in the laboratory work is 68% nitric acid by mass in aqueous is 1.504 g mL^-1?

8 Arrange the following aqueous solution, each of strength 0.1 M, in order of increasing freezing and boiling points. Justify your answer.

C₂H₅OH, Ba₃(PO₄)₂, Na₂SO₄, KCI, Li₃PO₄

3 Marks Questions

9 State Henry’s law for solubility of a gas in a liquid Explain the significance of Henry’s law constant (K_H), At the same temperature, hydrogen is more soluble in water than helium. Which of them will have a higher value of K_H and why ?

10 At 298 K, the vapour pressure of pure water is 23.75 mm Hg,

(a) At the same temperature, calculate the vapour pressure over 10% aqueous solution of an organic compound whose molecular weight is 60 g mol^-1?

(b) What will be the osmotic pressure of this solution at 298 K ? [R=0.082 L atm K^-1 mol^-1]

11 Two elements A and B form compounds having molecular formula AB₂ and AB_4. When dissolved in 20g of C₆H₆, 1g of AB₂ lowers the freezing point by 2.3 K, whereas 1.0g of AB₄ lowers it by 1.3 K. The molar depression constant for benzene is 5.1 K kg mol^-1. Calculate atomic mass of A and B.

5 Marks Questions

12 ( a ) What is meant by a ‘colligative property’?

      ( b ) Why does the presence of a solute in a solvent depress its freezing point?

      ( c ) The freezing point of pure nitrobenzene is 278.8 K. when 2.5 g of an unknown substance was dissolved in 100 g of nitrobenzene, the freezing point of solution was found to be 276.8 K. The freezing point depression constant of nitrobenzene is 8.0 K kg mol^-1. Calculate the molar mass of the unknown solute.