CH11-12 Exam Dr. Myton Fall 1998 SHOW ALL WORK

 

 

1. How many atoms are contained in 1.4 moles of CaCl2?

 

 

 

 

 

2. Calculate the solubility of carbon dioxide in g · L–1 at 20oC in a closed container of water if the partial pressure of CO2(g) is 3.6 atm. Henry's constant is 0.023 mol · L–1 · atm–1 for CO2(g) at 20oC.

 

 

 

 

 

____ 3. The equilibrium

Ca(HCO3)2(aq) « CaCO3(s) + CO2(g) + H2O(l)

exists during the formation of stalactites and stalagmites, which are mainly CaCO3(s), in underground caves. If a cave was opened to the atmosphere, predict the effect of the increased partial pressure of carbon dioxide.

a) The Ca(HCO3)2(aq) concentration would decrease.

b) The stalactites and stalagmites would become smaller due to dissolution of CaCO3(s).

c) More CaCO3(s) would be produced and the stalactites and stalagmites would become larger.

d) More CO2(g) and H2O(l) would be produced.

e) No change would occur.

 

 

4. The lattice enthalpy of AgF is 971 kJ · mol–1 and the hydration enthalpy is –993 kJ · mol–1. Estimate the enthalpy of solution of AgF.

 

 

 

 

 

____ 5. For AgCl, the lattice enthalpy is larger than the absolute value of the enthalpy of hydration. This means that for AgCl

a) the enthalpy of hydration is endothermic.

b) the enthalpy of solution is exothermic.

c) the enthalpy of solution is endothermic.

d) the lattice enthalpy is exothermic.

e) the solubility increases when the temperature decreases.

 

 

____ 6. Which of the following has the highest boiling point? Why?

a) F2 b) I2 c) Ar d) Br2 e) Cl2

 

 

____ 7. Which of the following species is likely to forn hydrogen bonds in the pure state? Why?

a) CH3C(O)CH3 b) CH3OCH3 c) CH3CH2OH d) (CH3)3N e) CH4

 

 

____ 8. Which of the following has the highest vapor pressure at room temperature? Explain your selection.

a) methanol, CH3OH d) water, H2O

b) dimethylether, CH3OCH3 e) acetic acid, CH3COOH

c) ethanol, CH3CH2OH

 

 

9. The vapor pressure of water above 50 mL of water in a 60-mL closed container is 23.8 Torr at 25oC. What is the vapor pressure of water if the volume of the container is changed to 100 mL?

 

 

 

 

 

10. Calculate the mole fraction of methanol, CH3OH, in a mixture of equal masses of methanol and water. The molar mass of methanol is 32.0 g · mol–1 and that of water is 18.0 g · mol–1.

 

 

 

 

 

____ 11. When the mole fraction of solute is 1.0, there is

a) 1.0 mole of solute and 99 moles of solvent. d) only solvent present.

b) 1.0 g of solute per 100 g of solution. e) only solute present.

c) a 1:1 ratio of solute to solvent.

 

 

12. Commercial nitric acid (molar mass, 63.0 g · mL–1) has a density of 1.42 g/mL. If the molarity of HNO3(aq) is 16.0 M, calculate the molality of HNO3(aq).

 

 

 

 

 

13. Calculate the vapor pressure at 80oC of a solution prepared by dissolving 3.00 moles of glucose in 200 g of water. The vapor pressure of water at 80oC is 355 Torr and the molar mass of water is 18.0 g · mol–1.

 

 

 

 

 

14. A solution made up of 50.0 g each of CS2 (molar mass, 76.13 g · mol–1) and CCl4 (molar mass, 153.8 g · mol–1) has a vapor pressure of 274 Torr at 296 K. If the vapor pressure of pure carbon disulfide is 360 Torr at 296 K, what is the vapor pressure of pure carbon tetrachloride?

 

 

 

 

 

____ 15. Which of the following has the lowest freezing point and the highest boiling point?

a) 1.5 m aluminum nitrate d) 1.5 m calcium chloride

b) 1.0 m acetic acid e) 2.0 m potassium chloride

c) 1.0 m sodium chloride

 

 

____ 16. A 1.0 m aqueous solution of an unknown solute has a freezing point of –9.30oC. Which of the following is the solute? The kf for water is 1.86 K · kg · mol–1.

a) calcium chloride d) sodium chloride

b) aluminum sulfate e) sodium sulfate

c) iron(III) chloride

 

 

17. The addition of 125 mg of caffeine to 100 g of cyclohexane lowered the freezing point by 0.13 K. Calculate the molar mass of caffeine. The kf for cyclohexane is 20.1 K · kg · mol–1.

 

 

 

 

 

18. Blood, sweat, and tears are about 0.15 M in sodium chloride. Estimate the osmotic pressure of these solutions at 37oC. The gas constant is 0.0821 L · atm · K–1 · mol–1.(Hint: The effective molarity of all particles must be used.)

 

 

 

 

 

19. Hexane, C6H14, a component of paint thinners, has an enthalpy of vaporization of 30.1 kJ/mol. At 25oC the vapor pressure of hexane is 148 torr. What is the vapor pressure at 15oC?

 

 

 

 

 

20. Water has a molar heat of vaporization of 40.7 kJ/mol, and a specific heat of 4.184 J/goC. How much energy is needed to vaporize (convert to vapor at 100oC) 1 mole of 25oC water.

 

 

 

 

 

 

 

Answer Key -- Fall98 ch11-12 brady

1. 2.53e24

2. 3.7 g · L–1

3. b The stalactites and stalagmites would become smaller due to dissolution of CaCO3(s).

4. –22 kJ · mol–1

5. c the enthalpy of solution is endothermic.

6. b I2

7. c CH3CH2OH

8. b dimethylether, CH3OCH3

9. 23.8 Torr

10. 0.360

11. e only solute present.

12. 39 m

13. 279 Torr

14. 100 Torr

15. a 1.5 m aluminum nitrate

16. b aluminum sulfate

17. 193 g/mol

18. 7.6 atm

19. 97.06 torr

20. 5648+40700 = 46.35 kJ