MCQs on Freezing Point of the Solvent

The normal freezing point of a pure liquid is the temperature at which the vapour pressure of the solid is equal to the vapour pressure of the liquid at atmospheric pressure. At the freezing point of a solvent, the solid and the liquid are in equilibrium. When a solution freezes, it is not the solution that solidifies but the pure solvent that freezes out from the solution.

Thus the freezing point of a solution is the temperature at which the vapour pressure of the solvent in the solid-state and the vapour pressure of the solution in the liquid state are equal. Since the vapour pressure of a solution is lower than that of the pure liquid solvent the solution and the solid solvent can be in equilibrium only if the vapour pressure of the solid solvent becomes lower.

1. Which one of the following gases has the lowest value of Henry’s law constant?

1. N₂
2. He
3. H₂
4. CO₂

Answer: (d)

2. If 10ml of 0.1M aqueous solution of NaCl is divided into 1000 drops of equal volume. What will be the concentration of one drop?

1. 0.01M
2. 0.10M
3. 0.001M
4. 0.0001M

Answer: (b)

3. A 0.5 molal solution of ethylene glycol in water is used as a coolant in a car. If the freezing point constant of water be 1.86^oC per mole, the mixture shall freeze at

1. 0.93^oC
2. -0.93^oC
3. 1.86^oC
4. -1.86^oC

Answer: (b)

4. Which statement is true for a solution of 0.020M H₂SO₃?

1. 2 litre of the solution contains 0.020 mole of SO₄^2-
2. 2 litre of the solution contains 0.080 mole of H₃O⁺
3. 1 litre of the solution contains 0.020 mole of H₃O⁺
4. None of these

Answer: (b)

5. A 500g toothpaste sample has 0.2g fluoride concentration. What is the concentration of F in terms of ppm level?

1. 250
2. 300
3. 400
4. 1000

Answer: (c)

6. If at a certain temperature the vapour pressure of pure water is 25 mm Hg and that of a very dilute aqueous urea solution is 24.5mm Hg, the molality of the solution is

1. 0.02
2. 1.2
3. 1.11
4. 0.08

Answer: (c)

7. Which of the following 0.10m aqueous solutions will have the lowest freezing point?

1. Al₂(SO₄)₃
2. C₆H₁₂O₆
3. KCl
4. C₁₂H₂₂O₁₁

Answer: (a)

8. The amount of urea to be dissolved in 500 cc of water (K = 1.86^oC mol^-1) to produce a depression of 0.186^oC in the freezing point is

1. 9g
2. 6g
3. 3g
4. 0.3g

Answer: (c)

9. The empirical formula of a nonelectrolyte is CH₂O. A solution containing 6g of the compound exerts the same osmotic pressure as that of 0.05M glucose solution at the same temperature, The molecular formula of the compound is

1. C₂H₄O₂
2. C₃H₆O₃
3. C₅H₁₀O₅
4. C₄H₈O₄

Answer: (d)

10. The molar mass of the solute sodium hydroxide obtained from the measurement of the osmotic pressure of its aqueous solution at 27^oC is 25gmol^-1. Therefore its ionization solution at 27^oC is 25 g mol^-1. Therefore its ionization percentage in this solution is

1. 75
2. 60
3. 80
4. 70

Answer: (b)

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