Q: A solution is made by mixing 20.0 mL of ethanol with enough water to make 100.0 mL of solution. What is the percent by volume of ethanol in the solution?

$$\frac{20.0}{100.0} \times 100 = 20\%$$

Question 1

Which of the following phase changes is exothermic?

Accepted Answer

Condensation

Question 2

A sample of solid carbon dioxide (dry ice) is left on a table at room temperature and disappears without leaving a liquid residue. Which process best describes this change?

Accepted Answer

Sublimation

Question 3

Which of the following substances would you expect to have the highest boiling point?

Accepted Answer

NH$$_3$$

Question 4

Which intermolecular force is primarily responsible for the high boiling point of water compared to hydrogen sulfide (H$$_2S$$)?

Accepted Answer

Hydrogen bonding

Question 5

A 50.0 g sample of ethanol (C$$_2H$_5OH) is $$dissolved in 200.0 g of water. What is the molality of the solution? (Molar mass of ethanol = 46.07 g/mol)

Accepted Answer

$$m = \frac{50.0}{46.07} \div 0.200 = 5.43\ m$$

Question 6

Which of the following statements about vapor pressure is correct?

Accepted Answer

A volatile liquid has a high vapor pressure.

Question 7

At the triple point of a substance, which of the following is true?

Accepted Answer

Solid, liquid, and gas phases coexist in equilibrium.

Question 8

A solution is prepared by dissolving 0.10 mol of NaCl in 1.0 kg of water. What is the expected van’t Hoff factor ($$i) $$for this solution?

Accepted Answer

$$i = 2$$

Question 9

Which of the following best explains why ice floats on liquid water?

Accepted Answer

The solid-liquid line in water’s phase diagram has a negative slope, indicating ice is less dense than liquid water.

Question 10

Calculate the boiling point of a solution made by dissolving 2.0 mol of CaCl$$_2 in 1.0 kg of $$water. ($$K_b = 0.512\ ^\circC/m$$, $$i = 3)$$

Accepted Answer

$$T_b = 100 + (3)(0.512)(2.0) = 103.072\ ^\circC$$

Question 11

Which of the following concentration units is most appropriate for calculating freezing point depression?

Accepted Answer

Molality (m)

Question 12

A solution contains 0.5 mol of glucose (a nonelectrolyte) dissolved in 1.0 kg of water. If $$K_f = 1.86\ ^\circC/m$$, what is the freezing point of the solution?

Accepted Answer

$$T_f = 0 - (1)(1.86)(0.5) = -0.93\ ^\circC$$

Question 13

Which of the following best describes what happens to the vapor pressure of a liquid as temperature increases?

Accepted Answer

Vapor pressure increases.

Question 14

A heating curve for a pure substance shows a flat region at 0$$^\circC. $$What is happening in this region?

Accepted Answer

The substance is undergoing a phase change from solid to liquid.

Question 15

Which of the following solutions will have the lowest freezing point? Assume equal molalities.

Accepted Answer

CaCl$$_2$$

Question 16

A chemist needs to prepare a solution with a concentration of 1 ppm Na$$^+$$ ions. How many milligrams of Na$$^+$$ should be dissolved in 1.0 L of water?

Accepted Answer

1 mg

Question 17

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

Accepted Answer

Salt decreases the freezing point of water by increasing the number of solute particles.

Question 18

A solution is made by mixing 20.0 mL of ethanol with enough water to make 100.0 mL of solution. What is the percent by volume of ethanol in the solution?

Accepted Answer

$$\frac{20.0}{100.0} 	imes 100 = 20\%$$

Question 19

Which of the following best describes a supercritical fluid?

Accepted Answer

A state where the liquid and gas phases are indistinguishable.

Question 20

A 10.0 g sample of NaCl (molar mass = 58.44 g/mol) is dissolved in 100.0 g of water. What is the mole fraction of NaCl in the solution?

Accepted Answer

$$\chi_{NaCl} = \frac{0.171}{0.171 + 5.56} = 0.030$$

General Chemistry Study Guide: Phases, Intermolecular Forces, and Solutions (Chapters 11 & 13)

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