Q: Which of the following correctly expresses the molality ($$m) of a $$solution?

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

Q: Which equation correctly represents Raoult’s Law for vapor pressure lowering?

$$P_{\text{solution}} = X_{\text{solvent}} P$$^{\circ}$$_{\text{solvent}}$$

Q: Which of the following is the correct formula for mass percent of a solute in a solution?

$$\text{Mass \%} = \frac{\text{mass of solute}}{\text{total mass of solution}} \times 100$$

Q: Which of the following is the correct formula for calculating mole fraction ($$X) of a $$component in a solution?

$$X = \frac{\text{moles of component}}{\text{total moles of all components}}$$

Question 1

The Environmental Protection Agency (EPA) requires action when the concentration of lead (Pb$$^{2+}) in $$water exceeds 15 ppb. What is the maximum mass of lead that could be present in 1.00 L of water before exceeding this limit? Assume the density of water is 1.00 g/cm$$^3.$$

Accepted Answer

$$0.015 mg$$

Question 2

Which of the following correctly expresses the molality ($$m) of a $$solution?

Accepted Answer

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

Question 3

A bottle of gin is labeled as 44% alcohol by volume. If you have 1.000 L of this gin, and the density of ethanol is $$0.789 g/mL$$, what is the mass of ethanol in the solution?

Accepted Answer

$$347 g$$

Question 4

Which equation correctly represents Raoult’s Law for vapor pressure lowering?

Accepted Answer

$$P_{	ext{solution}} = X_{	ext{solvent}} P$$^{\circ}$$_{	ext{solvent}}$$

Question 5

A solution is made by dissolving $$22.5 g of $$lactose ($$\mathrm{C$$_{12}$$H_{22}O$$_{11}}$$) in 100.0$ g of water at 25$$^{\circ}$$C. The vapor pressure of pure water at this temperature is 23.8$ torr. What is the vapor pressure of the solution?

Accepted Answer

$$23.5$$ 	ext{ torr}$

Question 6

Which of the following best describes a colligative property?

Accepted Answer

A property that depends on the concentration of solute particles but not their identity.

Question 7

Which solution will have the lowest freezing point? (All are $$0.15 m $$aqueous solutions.)

Accepted Answer

The $$\mathrm{Zn(NO_3$)_2}$$ solution

Question 8

What is the correct formula for calculating the boiling point elevation of a solution?

Accepted Answer

$$\Delta T_b = i K_b m$$

Question 9

A $$0.05 m $$solution of $$\mathrm{$$MgCl_2$$} in $$water has a measured freezing point depression of $$-0.25^{\circ}C. If$$ $$K_f$$ for water is $$1.86$$ $$^{\circ}C/m$$, what is the van’t Hoff factor $$i$$ for this solution?

Accepted Answer

$$i = 2.7$$

Question 10

Which of the following best explains why salt is spread on icy roads in winter?

Accepted Answer

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

Question 11

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

Accepted Answer

$$\Pi = i M R T$$

Question 12

If a solution is prepared by mixing $$347 g of $$ethanol ($$\mathrm{CH_3CH_2OH}) $$and $$559 g of $$water, what is the mole fraction of ethanol?

Accepted Answer

$$0.195$$

Question 13

A solution contains two volatile components, A and B. If $$X_A = 0.7$$, $$P_A$$^{\circ}$$ = 100$$ torr, $$X_B = 0.3$$, and $$P_B$$^{\circ}$$ = 50$$ torr, what is the total vapor pressure above the solution?

Accepted Answer

$$85$$ 	ext{ torr}$

Question 14

Which of the following is NOT a colligative property?

Accepted Answer

Color of the solution

Question 15

If $$7.53$$ mol of ethanol is dissolved in $$0.559 kg of $$water, what is the molality of the solution?

Accepted Answer

$$13.47$$ 	ext{ m}$

Question 16

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

Accepted Answer

The vapor pressure of the solvent decreases.

Question 17

Which of the following is the correct formula for mass percent of a solute in a solution?

Accepted Answer

$$	ext{Mass \%} = \frac{	ext{mass of solute}}{	ext{total mass of solution}} 	imes 100$$

Question 18

Which of the following best explains why the van’t Hoff factor ($$i) $$for NaCl is less than 2 at higher concentrations?

Accepted Answer

Ion pairing reduces the number of effective particles in solution.

Question 19

A solution is prepared by dissolving $$10 g of $$NaCl in $$100 g of $$water. Which concentration unit would be most appropriate for expressing the concentration of NaCl for environmental monitoring of trace contaminants?

Accepted Answer

Parts per million (ppm)

Question 20

Which of the following is the correct formula for calculating mole fraction ($$X) of a $$component in a solution?

Accepted Answer

$$X = \frac{	ext{moles of component}}{	ext{total moles of all components}}$$

Solution Concentration and Colligative Properties

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