14. Solutions

Which of the following solutions has the lowest vapor pres- sure? (Assume complete dissociation for ionic compounds.) (LO 13.10) (a) An aqueous solution of 0.25 m Ca1NO322 (b) An aqueous solution of 0.30 m sodium chloride (NaCl) (c) A mixture of 50 mL of water and 50 mL of ethanol 1CH3CH2OH2 (d) A mixture of 25 mL of water and 50 mL of ethanol 1CH3CH2OH2

Assume that you have a liquid in a cylinder equipped with a movable piston. There is no air in the cylinder, the volume of space above the liquid is 200 mL, and the equilibrium vapor pressure above the liquid is 28.0 mm Hg. What is the equilibrium pressure above the liquid when the volume of space is decreased from 200 mL to 100 mL at constant temperature?

The following phase diagram shows part of the vapor- pressure curves for a pure liquid (green curve) and a solution of the first liquid with a second volatile liquid (red curve).

(a) Is the boiling point of the second liquid higher or lower than that of the first liquid?

Two beakers, one with pure water (blue) and the other with a solution of NaCl in water (green), are placed in a closed container as represented by drawing (a). Which of the draw- ings (b)–(d) represents what the beakers will look like after a substantial amount of time has passed?

You make a solution of a nonvolatile solute with a liquid solvent. Indicate if each of the following statements is true or false. (b) The solid that forms as the solution freezes is nearly pure solute.

You make a solution of a nonvolatile solute with a liquid solvent. Indicate if each of the following statements is true or false. (a) The freezing point of the solution is unchanged by addition of the solvent.

You make a solution of a nonvolatile solute with a liquid solvent. Indicate if each of the following statements is true or false. (d) The boiling point of the solution increases in proportion to the concentration of the solute.

(a) Does a 0.10 m aqueous solution of NaCl have a higher boiling point, a lower boiling point, or the same boiling point as a 0.10 m aqueous solution of C6H12O6?

Which solution has the highest vapor pressure? a. 20.0 g of glucose (C6H12O6) in 100.0 mL of water b. 20.0 g of sucrose (C12H22O11) in 100.0 mL of water c. 10.0 g of potassium acetate KC2H3O2 in 100.0 mL of water

List the following aqueous solutions in order of increasing boiling point: 0.120 m glucose, 0.050 m LiBr, 0.050 m Zn1NO322.

A solution contains 50.0 g of heptane (C7H16) and 50.0 g of octane (C8H18) at 25 °C. The vapor pressures of pure heptane and pure octane at 25 °C are 45.8 torr and 10.9 torr, respectively. Assuming ideal behavior, answer the following: d. Why is the composition of the vapor different from the composition of the solution?

When 1 mL of toluene is added to 100 mL of benzene (bp 80.1 °C), the boiling point of the benzene solution rises, but when 1 mL of benzene is added to 100 mL of toluene (bp 110.6 °C), the boiling point of the toluene solution falls. Explain.

A solution concentration must be expressed in molality when considering boiling-point elevation or freezing-point depression but can be expressed in molarity when consider- ing osmotic pressure. Why?

Two beakers are placed in a sealed box at 25 °C. One beaker contains 30.0 mL of a 0.050 M aqueous solution of a nonvolatile nonelectrolyte. The other beaker contains 30.0 mL of a 0.035 M aqueous solution of NaCl. The water vapor from the two solutions reaches equilibrium. (a) In which beaker does the solution level rise, and in which one does it fall?

13.122 When salt is spread on snow-covered roads at - 2 °C, the snow melts. When salt is spread on snow-covered roads at - 30 °C, nothing happens. Explain.

If cost per gram were not a concern, which of the following substances would be the most efficient per unit mass for melting snow from sidewalks and roads: glucose 1C6H12O62, LiCl, NaCl, or CaCl2? Explain.

Assuming equal concentrations and complete dissociation, arrange these aqueous solutions by their freezing points.