Q: A solution is prepared by dissolving 10 g of a nonvolatile solute in 100 g of water. If the mole fraction of water is 0.95 and the vapor pressure of pure water is 25 torr, what is the vapor pressure of the solution?

$$P_{solution} = 25 \times 0.95 = 23.75$$ torr

Q: A solution is made by dissolving 0.1 mol of glucose in 1 kg of water. If $$k_f$$ for water is $$1.86 \ ^\circ C/m$$, what is the freezing point of the solution?

$$0.00 \ ^\circ C - (1.86 \times 0.1) = -0.186 \ ^\circ C$$

Q: What is the osmotic pressure ($$\pi) of a $$solution with a molarity of $$0.01 M at$$ $$25 \ ^\circ C$$? (Use $$R = 0.0821 \ L \cdot atm / K \cdot mol)$$

$$\pi = 0.01 \times 0.0821 \times 298 = 0.244$$ atm

Q: A solution contains 0.2 mol NaCl in 1 kg water. What is the expected freezing point depression? ($$k_f = 1.86 \ ^\circ C/m$$, $$i = 2$$ for NaCl)

$$\Delta T_f = 1.86 \times 0.2 \times 2 = 0.744 \ ^\circ C$$

Question 1

Which statement best explains the effect of adding a nonvolatile solute to a solvent, as illustrated in the first image?

Accepted Answer

The vapor pressure of the solution decreases because fewer solvent molecules can escape into the gas phase.

Question 2

According to Raoult’s Law, what is the formula for the vapor pressure of a solution containing a nonvolatile solute?

Accepted Answer

$$P_{solution} = P_{solvent}^\circ \cdot X_{solvent}$$

Question 3

A solution is prepared by dissolving 10 g of a nonvolatile solute in 100 g of water. If the mole fraction of water is 0.95 and the vapor pressure of pure water is 25 torr, what is the vapor pressure of the solution?

Accepted Answer

$$P_{solution} = 25 	imes 0.95 = 23.75$$ torr

Question 4

Which scenario would result in a positive deviation from Raoult’s Law, as shown in the third vapor pressure diagram?

Accepted Answer

Weak solute-solvent interactions

Question 5

What is the effect of adding a nonvolatile solute on the boiling point of a solvent, as shown in the phase diagram?

Accepted Answer

The boiling point increases because the vapor pressure is lowered.

Question 6

Which equation correctly describes boiling point elevation?

Accepted Answer

$$\Delta T_b = k_b m$$

Question 7

A solution is made by dissolving 0.1 mol of glucose in 1 kg of water. If $$k_f$$ for water is $$1.86 \ ^\circ C/m$$, what is the freezing point of the solution?

Accepted Answer

$$0.00 \ ^\circ C - (1.86 	imes 0.1) = -0.186 \ ^\circ C$$

Question 8

Which property is used in cryoscopy to determine the molar mass of a solute?

Accepted Answer

Freezing point depression

Question 9

What is the osmotic pressure ($$\pi) of a $$solution with a molarity of $$0.01 M at$$ $$25 \ ^\circ C$$? (Use $$R = 0.0821 \ L \cdot atm / K \cdot mol)$$

Accepted Answer

$$\pi = 0.01 	imes 0.0821 	imes 298 = 0.244$$ atm

Question 10

A red blood cell placed in a hypotonic solution will:

Accepted Answer

Swell and possibly burst due to water entering the cell.

Question 11

What is the van’t Hoff factor ($$i) $$for CaCl$$_2 in $$water, assuming complete dissociation?

Accepted Answer

$$i = 3$$

Question 12

How does the van’t Hoff factor ($$i) $$affect the calculation of colligative properties for electrolyte solutions?

Accepted Answer

It multiplies the property value, increasing the effect.

Question 13

A solution contains 0.2 mol NaCl in 1 kg water. What is the expected freezing point depression? ($$k_f = 1.86 \ ^\circ C/m$$, $$i = 2$$ for NaCl)

Accepted Answer

$$\Delta T_f = 1.86 	imes 0.2 	imes 2 = 0.744 \ ^\circ C$$

Question 14

Why do experimentally determined van’t Hoff factors ($$i) $$for electrolytes often differ from theoretical values at higher concentrations?

Accepted Answer

Because ion pairs form, reducing the number of free particles.

Question 15

Which of the following is NOT a colligative property?

Accepted Answer

Solubility of the solute

Question 16

A solution is made by dissolving 0.1 mol K$$_2SO$_4 in 1 kg $$water. If $$k_f = 1.86 \ ^\circ C/m$$ and $$i = 3$$ for K$$_2SO$_4$$, what is the freezing point depression?

Accepted Answer

$$\Delta T_f = 1.86 	imes 0.1 	imes 3 = 0.558 \ ^\circ C$$

Question 17

Which concentration unit is preferred for colligative property calculations and why?

Accepted Answer

Molality, because it is not temperature dependent.

Question 18

What is the main reason why the addition of salt to icy roads helps to melt the ice in winter?

Accepted Answer

Salt decreases the freezing point of water, causing ice to melt at lower temperatures.

Colligative Properties of Solutions: Mini-Textbook Study Guide

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