Elevation of boiling point and depression of freezing point — practice questions

Question 1 · difficulty L2 · understanding

A solution containing $$2 \mathrm{~g}$$ of a non-volatile solute in $$20 \mathrm{~g}$$ of water boils at $$373.52 \mathrm{~K}$$. The molecular mass of the solute is ___________ $$\mathrm{g} ~\mathrm{mol}^{-1}$$. (Nearest integer) Given, water boils at $$373 \mathrm{~K}, \mathrm{~K}_{\mathrm{b}}$$ for water $$=0.52 \mathrm{~K} \mathrm{~kg} \mathrm{~mol}^{-1}$$

Question 2 · difficulty L2 · understanding

$$1.80 \mathrm{~g}$$ of solute A was dissolved in $$62.5 \mathrm{~cm}^{3}$$ of ethanol and freezing point of the solution was found to be $$155.1 \mathrm{~K}$$. The molar mass of solute A is ________ g $$\mathrm{mol}^{-1}$$. [Given : Freezing point of ethanol is 156.0 K. Density of ethanol is 0.80 g cm $$-$$3 . Freezing point depression constant of ethanol is 2.00 K kg mol $$-$$1 ]

Question 3 · difficulty L2 · understanding

$$150 \mathrm{~g}$$ of acetic acid was contaminated with $$10.2 \mathrm{~g}$$ ascorbic acid $$\left(\mathrm{C}_{6} \mathrm{H}_{8} \mathrm{O}_{6}\right)$$ to lower down its freezing point by $$\left(x \times 10^{-1}\right)^{\circ} \mathrm{C}$$. The value of $$x$$ is ___________. (Nearest integer) [Given $$\mathrm{K}_{f}=3.9 \mathrm{~K} \mathrm{~kg} \mathrm{~mol}^{-1}$$; molar mass of ascorbic acid $$=176 \mathrm{~g} \mathrm{~mol}^{-1}$$]

Question 4 · difficulty L2 · understanding

The elevation in boiling point for 1 molal solution of non-volatile solute A is $$3 \mathrm{~K}$$. The depression in freezing point for 2 molal solution of $$\mathrm{A}$$ in the same solvent is 6 $$K$$. The ratio of $$K_{b}$$ and $$K_{f}$$ i.e., $$K_{b} / K_{f}$$ is $$1: X$$. The value of $$X$$ is [nearest integer]

Question 5 · difficulty L2 · understanding

A solution containing 2.5 $$\times$$ 10 $$-$$3 kg of a solute dissolved in 75 $$\times$$ 10 $$-$$3 kg of water boils at 373.535 K. The molar mass of the solute is ____________ g mol $$-$$1 . [nearest integer] (Given : K b (H 2 O) = 0.52 K kg mol $$-$$1 and boiling point of water = 373.15 K)

Question 6 · difficulty L2 · understanding

40 g of glucose (Molar mass = 180) is mixed with 200 mL of water. The freezing point of solution is __________ K. (Nearest integer) [Given : K f = 1.86 K kg mol $$-$$1 ; Density of water = 1.00 g cm $$-$$3 ; Freezing point of water = 273.15 K]

Question 7 · difficulty L2 · understanding

83 g of ethylene glycol dissolved in 625 g of water. The freezing point of the solution is ____________ K. (Nearest integer) [Use : Molal Freezing point depression constant of water = 1.86 K kg mol $$-$$1 ] Freezing Point of water = 273 K Atomic masses : C : 12.0 u, O : 16.0 u, H : 1.0 u]

Question 8 · difficulty L2 · understanding

When 3.00 g of a substance 'X' is dissolved in 100 g of CCl 4 , it raises the boiling point by 0.60 K. The molar mass of the substance 'X' is ______________ g mol $$-$$1 . (Nearest integer). [Given K b for CCl 4 is 5.0 K kg mol $$-$$1 ]

Question 9 · difficulty L2 · understanding

2 moles each of ethylene glycol and glucose are dissolved in 500 g of water. The boiling point of the resulting solution is: (Given : Ebullioscopic constant of water $=0.52 \mathrm{~K} \mathrm{~kg} \mathrm{~mol}^{-1}$ )

• A. 377.3 K
• B. 379.2 K
• C. 375.3 K
• D. 277.3 K

Question 10 · difficulty L2 · understanding

Given below are two statements : Statement (I): NaCl is added to the ice at 0°C, present in the ice cream box to prevent the melting of ice cream. Statement (II): On addition of NaCl to ice at 0°C, there is a depression in freezing point. In the light of the above statements, choose the correct answer from the options given below :

• A. Both Statement I and Statement II are false
• B. Statement I is true but Statement II is false
• C. Both Statement I and Statement II are true
• D. Statement I is false but Statement II is true