Q: A solution is made by dissolving 4.00 g of NaOH (molar mass = 40 g/mol) in 250 g of water. What is the molality ($$b) of $$the solution?

$$b = \frac{0.10\ \text{mol}}{0.250\ \text{kg}} = 0.40\ \text{mol/kg}$$

Q: Which equation correctly expresses Raoult’s Law for the vapour pressure of a solution?

$$P_\text{solution} = x_\text{solvent} \times P_\text{solvent}$$

Q: A 10% (by mass) aqueous solution of sugar ($$\mathrm{C$$_{12}$$H_{22}O$$_{11}}$$) is prepared by dissolving 10 g of sugar in 90 g of water. What is the molality (b$) of the solution? (Molar mass of sugar = 342.3 g/mol)

$$b = \frac{0.029\ \text{mol}}{0.090\ \text{kg}} = 0.32\ \text{mol/kg}$$

Q: Which of the following is the correct formula for calculating the freezing point depression ($$\Delta T_{freezing}) of a $$solution?

$$\Delta T_{freezing} = K_f \times b$$

Question 1

Which of the following statements best describes a colligative property?

Accepted Answer

A property that depends on the amount of solute particles present, not their identity.

Question 2

Why is molality ($$b) $$preferred over molarity ($$M) $$when calculating colligative properties?

Accepted Answer

Because molality is based on the mass of solvent, which does not change with temperature.

Question 3

A solution is made by dissolving 4.00 g of NaOH (molar mass = 40 g/mol) in 250 g of water. What is the molality ($$b) of $$the solution?

Accepted Answer

$$b = \frac{0.10\ 	ext{mol}}{0.250\ 	ext{kg}} = 0.40\ 	ext{mol/kg}$$

Question 4

Which equation correctly expresses Raoult’s Law for the vapour pressure of a solution?

Accepted Answer

$$P_	ext{solution} = x_	ext{solvent} 	imes P_	ext{solvent}$$

Question 5

A 10% (by mass) aqueous solution of sugar ($$\mathrm{C$$_{12}$$H_{22}O$$_{11}}$$) is prepared by dissolving 10 g of sugar in 90 g of water. What is the molality (b$) of the solution? (Molar mass of sugar = 342.3 g/mol)

Accepted Answer

$$b = \frac{0.029\ 	ext{mol}}{0.090\ 	ext{kg}} = 0.32\ 	ext{mol/kg}$$

Question 6

Which of the following will have the greatest effect on the freezing point depression of water, assuming equal molal concentrations?

Accepted Answer

Ammonium sulfate ($$\mathrm{(NH_4$)_2SO_4})$$

Question 7

A red blood cell is placed in a hypotonic solution. What is the most likely outcome?

Accepted Answer

The cell will gain water and swell, possibly bursting.

Question 8

Which of the following best explains why adding salt to icy roads helps to melt the ice?

Accepted Answer

Salt decreases the freezing point of water, so ice melts at a lower temperature.

Question 9

Calculate the boiling point of a solution made by dissolving 0.50 mol of NaCl in 1.00 kg of water. ($$K_b$$ for water = $$0.51\ \mathrm{K\ $$mol^{-1}$$\ kg}$$, boiling point of pure water = $$100.00\ ^\circ\mathrm{C}). $$Assume complete dissociation.

Accepted Answer

Question 10

Which of the following is the correct formula for calculating the freezing point depression ($$\Delta T_{freezing}) of a $$solution?

Accepted Answer

$$\Delta T_{freezing} = K_f 	imes b$$

Question 11

A solution contains 0.20 mol of ethanol and 0.80 mol of water. What is the mole fraction of ethanol ($$x_{ethanol}$$)?

Accepted Answer

$$x_{ethanol} = \frac{0.20}{0.20 + 0.80} = 0.20$$

Question 12

Which of the following scenarios best illustrates osmosis?

Accepted Answer

Water moving from a region of low solute concentration to high solute concentration through a semipermeable membrane.

Question 13

Which of the following is NOT a colligative property?

Accepted Answer

Color change of the solution

Question 14

A solution is prepared by dissolving 1.0 mol of glucose ($$\mathrm{C_6H_{12}O_6$}) $$and 1.0 mol of NaCl in 1.0 kg of water. How many total solute particles are present, assuming complete dissociation of NaCl?

Accepted Answer

3.0 mol

Question 15

Which of the following best describes the effect of adding a nonvolatile solute to a solvent?

Accepted Answer

The vapour pressure decreases, boiling point increases, and freezing point decreases.

Question 16

Which of the following medical scenarios is a direct result of osmosis?

Accepted Answer

A patient receiving an intravenous solution that is not isotonic, causing their red blood cells to swell and burst.

Question 17

Which of the following equations correctly relates osmotic pressure ($$\Pi) to $$solute concentration for dilute solutions?

Accepted Answer

$$\Pi = iMRT$$

Question 18

A cucumber is placed in a concentrated NaCl solution and loses water, becoming a pickle. Which process is responsible for this transformation?

Accepted Answer

Osmosis, with water moving out of the cucumber cells into the NaCl solution.

Colligative Properties of Solutions: Concepts, Calculations, and Applications

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