Question 1

Which of the following best explains why the vapor pressure of an aqueous solution (right flask in image 1) is lower than that of pure water (left flask in image 1)?

Accepted Answer

The solute particles occupy space at the surface, reducing the number of water molecules that can escape into the vapor phase.

Question 2

According to Raoult’s Law, what is the correct formula for the partial vapor pressure of component A in an ideal solution?

Accepted Answer

$$P_A = \chi_A P_A^*$$

Question 3

Refer to the graph of vapor pressure vs. mole fraction for an ideal solution (image 2). What does the straight line for the vapor pressure of the solution indicate?

Accepted Answer

The solution follows Raoult’s Law and the intermolecular forces between all components are similar.

Question 4

Which equation correctly represents the total vapor pressure of a solution containing two volatile components, A and B?

Accepted Answer

$$P_{total} = \chi_A P_A^* + \chi_B P_B^*$$

Question 5

In the context of non-ideal solutions, what does a vapor pressure curve below the Raoult’s Law prediction (image 4) indicate about solute-solvent interactions?

Accepted Answer

Solute-solvent interactions are stronger than solute-solute and solvent-solvent interactions.

Question 6

Which real-world process is best illustrated by the laboratory setup in image 6?

Accepted Answer

Distillation

Question 7

In the context of fractional distillation (image 7), why do smaller molecules tend to be collected at the top of the column?

Accepted Answer

They have lower boiling points and are more volatile.

Question 8

Which equation describes the boiling point elevation for a solution?

Accepted Answer

$$\Delta T_b = m 	imes K_b$$

Question 9

A solution is prepared by dissolving 15.6 g of ethanol (FW 46.07 g/mol) in 625 g of water. If the boiling point elevation constant for water is $$0.512\ ^\circ C\ kg\ $$mol^{-1}$$, what is the boiling point elevation?

Accepted Answer

$$0.277\ ^\circ C$$

Question 10

Which of the following best describes the process of osmosis as shown in image 12?

Accepted Answer

Solvent moves from the pure solvent side to the solution side through a semipermeable membrane.

Question 11

Which equation is used to calculate the osmotic pressure of a solution?

Accepted Answer

$$\Pi = iMRT$$

Question 12

A 0.085 M aqueous solution of $$Ca($$ClO_3$$)_2 at 298 K $$has an osmotic pressure of approximately:

Accepted Answer

$$6.3$$ atm

Question 13

Which of the following statements about the van’t Hoff factor ($$i) is $$correct?

Accepted Answer

It is the ratio of the observed colligative property to the expected value for a non-electrolyte.

Question 14

A solution of $$CaCl_2 is $$prepared with a molality of 1.5 m. What is the expected van’t Hoff factor ($$i) $$for $$CaCl_2$$ assuming complete dissociation?

Accepted Answer

3

Question 15

Which of the following best explains why the vapor pressure of a solution with weak solute-solvent interactions (image 5) is higher than predicted by Raoult’s Law?

Accepted Answer

The solute-solvent interactions are weaker, making it easier for molecules to escape into the vapor phase.

Question 16

Given the reaction $$2NH_3(g) \rightarrow N_2$(g) + 3H_2(g)$$, which expression correctly relates the rate of disappearance of $$NH_3 to $$the rate of appearance of $$H_2$$?

Accepted Answer

$$-\frac{1}{2} \frac{\Delta [NH_3$]}{\Delta t} = \frac{1}{3} \frac{\Delta [H_2$]}{\Delta t}$$

Question 17

A nonvolatile solute with empirical formula $$CH_2O is $$dissolved in 100.00 mL of water, raising the boiling point by $$0.20\ ^\circ C. If$$ $$K_b$$ for water is $$0.512\ ^\circ C\ kg\ $$mol^{-1}$$, what is the molar mass of the solute?

Accepted Answer

$$180\ g/mol$$

Question 18

Which of the following best describes the effect of adding a nonvolatile solute to a solvent on the freezing and boiling points of the solution?

Accepted Answer

The freezing point decreases and the boiling point increases.

Question 19

Which of the following is a correct statement about the rate of a chemical reaction?

Accepted Answer

It can be measured as the rate of appearance of a product or disappearance of a reactant, normalized by stoichiometry.

L16: Colligative Properties and Reaction Rates: Study Notes for General Chemistry

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