Q: What is the correct formula for calculating molality ($m$)?

$m = \frac{\text{moles of solute}}{\text{kilograms of solvent}}$

Question 1

Which of the following statements best describes a colligative property?

Accepted Answer

It depends on the concentration of the solute, not its identity.

Question 2

A solution is prepared by dissolving 22.5 g of lactose ($C_{12}H_{22}O_{11}$) in 100.0 g of water at 25°C. The vapor pressure of pure water at this temperature is 23.8 torr. What is the vapor pressure of the solution? (Molar mass of lactose = 342 g/mol)

Accepted Answer

$23.5$ torr

Question 3

Which equation correctly expresses Raoult’s Law for a solution with a nonvolatile solute?

Accepted Answer

$P_{solution} = X_{solvent} P^0_{solvent}$

Question 4

Which of the following is NOT a typical unit for expressing solution concentration?

Accepted Answer

Density percent

Question 5

A 1.00 L sample of water contains lead at a concentration of 15 ppb. What is the maximum mass of lead (in mg) present in the sample? (Assume density of water is $1.00 \ \mathrm{g/cm^3}$)

Accepted Answer

$0.015$ mg

Question 6

Which property is NOT a colligative property?

Accepted Answer

Color change

Question 7

What is the correct formula for calculating molality ($m$)?

Accepted Answer

$m = \frac{	ext{moles of solute}}{	ext{kilograms of solvent}}$

Question 8

Which equation describes the boiling point elevation of a solution?

Accepted Answer

$\Delta T_b = i K_b m$

Question 9

A solution is made by mixing two volatile liquids, A and B. According to Dalton’s Law of Partial Pressures, what is the total vapor pressure above the solution?

Accepted Answer

$P_{total} = X_A P_A^0 + X_B P_B^0$

Question 10

Which real-world scenario is most directly related to osmotic pressure?

Accepted Answer

Desalination of seawater

Question 11

If a solution is prepared by dissolving 7.53 mol of ethanol in 31.0 mol of water, what is the mole fraction of ethanol?

Accepted Answer

$0.195$

Question 12

Which of the following best explains why adding salt to ice causes the ice to melt at a lower temperature?

Accepted Answer

Salt lowers the freezing point of water due to freezing point depression, a colligative property.

Question 13

What is the van’t Hoff factor ($i$) for $NaCl$ in dilute aqueous solution?

Accepted Answer

$i = 2$

Question 14

Which formula is used to calculate osmotic pressure ($\Pi$) of a solution?

Accepted Answer

$\Pi = i M R T$

Question 15

A solution is made by dissolving 347 g of ethanol ($C_2H_5OH$) in 559 g of water. What is the mass percent of ethanol in the solution?

Accepted Answer

$38.3\%$

Question 16

Which of the following best describes why colligative properties are important in battery design?

Accepted Answer

They affect whether the battery will freeze or operate at low temperatures.

Question 17

Which concentration unit is most appropriate for expressing the concentration of a toxic metal in drinking water at very low levels?

Accepted Answer

Parts per billion (ppb)

Question 18

If the mole fraction of water in a solution is $0.988$, what is the mole fraction of all other components combined?

Accepted Answer

$0.012$

Question 19

Which of the following is a direct consequence of vapor pressure lowering in a solution?

Accepted Answer

The solution boils at a higher temperature than the pure solvent.

Solution Concentration and Colligative Properties

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