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

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

Q: If a solution is made by mixing two volatile liquids, how is the total vapor pressure above the solution calculated?

$$P_{\text{total}} = X_1$ P_1$^\circ + X_2$ P_2$^\circ$$

Q: Which of the following is the correct formula for molality?

$$\text{molality} = \dfrac{\text{moles of solute}}{\text{kilograms of solvent}}$$

Q: Which of the following is the correct formula for mass percent?

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

Q: Which of the following is the correct formula for mole fraction?

$$\text{Mole fraction} = \dfrac{\text{moles of solute}}{\text{total moles of all components}}$$

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 the solution is 1.00 g/cm$$^3.$$

Accepted Answer

$$0.015 mg$$

Question 2

A bottle of gin is labeled as 44% alcohol by volume. If you have 1.000 L of this gin, what is the molarity of ethanol ($$\mathrm{C_2H_5OH}) in $$the solution? (Density of ethanol = $$0.789 g/mL$$, molar mass = $$46.1 g/$$mol)

Accepted Answer

$$7.53 M$$

Question 3

Which of the following best describes a colligative property?

Accepted Answer

A property that depends only on the number of solute particles, not their identity.

Question 4

Which equation correctly expresses 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? (Molar mass of lactose = 342$ g/mol, water = 18.02$ g/mol)

Accepted Answer

$$23.5$$ 	ext{ torr}

Question 6

Which of the following solutions will have the lowest freezing point? All solutions are $$0.15 m in $$their respective solutes.

Accepted Answer

The $$0.15 m $$solution of $$\mathrm{Zn(NO_3$)_2}$$

Question 7

Which formula is used to calculate the boiling point elevation of a solution?

Accepted Answer

$$\Delta T_b = i K_b m$$

Question 8

A solution is prepared by mixing $$347 g of $$ethanol ($$\mathrm{C_2H_5OH}$$, molar mass $$46.1 g/$$mol) and $$559 g of $$water ($$\mathrm{H_2O}$$, molar mass $$18.0 g/$$mol). What is the mole fraction of ethanol in the solution?

Accepted Answer

$$0.195$$

Question 9

Which equation is used to calculate osmotic pressure?

Accepted Answer

$$\Pi = i M R T$$

Question 10

A $$0.05 m $$aqueous solution of $$\mathrm{$$MgCl_2$$}$$ 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

$$2.7$$

Question 11

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 12

If a solution is made by mixing two volatile liquids, how is the total vapor pressure above the solution calculated?

Accepted Answer

$$P_{	ext{total}} = X_1$ P_1$^\circ + X_2$ P_2$^\circ$$

Question 13

Which of the following is the correct formula for molality?

Accepted Answer

$$	ext{molality} = \dfrac{	ext{moles of solute}}{	ext{kilograms of solvent}}$$

Question 14

A solution contains $$0.15 m $$NaCl and $$0.15 m $$glycerin ($$\mathrm{C_3H_8O_3}). $$Which will have a greater effect on the freezing point of water and why?

Accepted Answer

NaCl, because it dissociates into more particles in solution.

Question 15

Which of the following is the correct formula for mass percent?

Accepted Answer

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

Question 16

Which of the following best describes why the vapor pressure of a solvent decreases when a nonvolatile solute is added?

Accepted Answer

The solute particles occupy surface sites, reducing the number of solvent molecules that can escape into the vapor phase.

Question 17

If the mole fraction of ethanol in a solution is $$0.195$$ and the vapor pressure of pure ethanol at $$20^{\circ}C is$$ $$45.0$$ torr, what is the partial pressure of ethanol above the solution?

Accepted Answer

$$8.78$$ 	ext{ torr}

Question 18

Which of the following is the correct formula for mole fraction?

Accepted Answer

$$	ext{Mole fraction} = \dfrac{	ext{moles of solute}}{	ext{total moles of all components}}$$

Solution Concentration and Colligative Properties

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