AT Chemistry
Chapter 11 Review Problems
1. A solution of phosphoric acid was made by dissolving 10.0 g H3PO4 in 100.0 mL
of water. The resulting volume was 104 mL. Calculate trhe density, mole
fraction, molarity, and molality of the solution. Assume water has a density of
1.00 g/cm3.
2. The lattice energy of NaI is -686 kJ/mol, and the enthalpy of hydration is -694
kJ/mol. Calculate the enthalpy of solution per mole of solid NaI. Describe the
process to which this enthalpy change applies.
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3. The density of a solution containing 75.0 grams of ethanol, C2H5OH, in 175.0
grams of water is 0.9575 g/mL. Assume the density of water to be 1.00 g/mL.
a) calculate the molarity of the ethanol/water solution:
b) calculate the molality of the solution:
c) calculate the mol fraction of alcohol:
d) calculate the weight percent ethanol
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4. Which solvent, water or hexane (C6H14), would you choose to dissolve each of
the following?
a) Cu(NO3)2
b) CS2
c) CH3C-OH
O
d) CH3(CH2)16CH2OH
e) HCl
f) C6H6
5. Calculate the solubility of O2 in water at a partial pressure of O2 of 120 torr at
25oC. The Henry’s law constant for O2 is 1.3 X 10-3 mol/L-atm for Henry’s law
in the form C = kP, where C is the gas concentration (mol/L).
6. The vapor pressure of a solution containing 53.6 g glycerin (C3H8O3) in 133.7 g
ethanol (C2H5OH) is 113 torr at 40oC. Calculate the vapor pressure of pure
ethanol at 40oC assuming that glycerin is a nonvolatile, nonelectrolyte solute in
ethanol.
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7. At a certain temperature, the vapor pressure of pure benzene (C6H6) is 0.930 atm.
A solution was prepared by dissolving 10.0 g of a nondissociating, nonvolatile
solute in 78.11 g of benzene at that temperature. The vapor pressure of the
solution was found to be 0.900 atm. Assuming the solution behaves ideally,
determine the molar massof the solute.
8. A solution of sodium chloride in water has a vapor pressure of 19.6 torr at 25oC.
What is the mole fraction of solute particles in this solution? What would be the
vapor pressure of this solution at 45oC? The vapor pressure of pure water is 23.8
torr at 25oC and 71.9 torr at 45oC and assume sodium chloride exists as Na+ and
Cl- ions in solution.
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9. Pentane (C5H12) and hexane (C6H14) form an ideal solution. At 25oC the vapor
pressures of pentane and hexane are 511 and 150. torr, respectively. A solution is
prepared by mixing 25 mL of pentane (density, 0.63 g/mL) with 45 mL hexane
(density, 0.66 g/mL).
a) What is the vapor pressure of the resulting solution?
b) What is the composition by mole fraction of pentane in the vapor that is in
equilibrium with this solution?
10. Benzene and toluene form an ideal solution. Consider a siolution of benzene and
toluene prepared at 25oC. Assuming the mole fractions of benzene and toluene in
the vapor phase are equal, calculate the composition of the solution. At 25oC the
vapor pressures of benzene and toluene are 95 and 28 torr, respectively.
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11. When 20.0 grams of a nonvolatile, nonelectrolyte is dissolved in 43 grams of nhexane, C6H14, the vapor pressure drops from 120 torr for pure hexane to 80 torr
for the solution. What is the molar mass of the unknown substance?
12. A 2.00-g sample of a large biomolecule was dissolved in 15.0 g carbon
tetrachloride. The boiling point of this solution was determined to be 77.85oC.
Calculate the molar mass of the biomolecule. For carbon tetrachloride, the
boiling-point constant is 5.03oC-kg/mol, and the boiling point of pure carbon
tetrachloride is 76.50oC.
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13. The freezing point of t-butanol is 25.50oC and Kf is 9.1oC-kg/mol. Usually tbutanol absorbs water on exposure to air. If the freezing point of a 10.0-g sample
of t-butanol is 254.59oC, how many grams of water are present in the sample?
14. An aqueous solution containing 0.250 mol Q, a strong electrolyte, in 500. g water
freezes at -2.79oC. What is the van’t Hoff factor for Q? The molal-freezing point
depression constant for water is 1.86oC-kg/mol. What is the formula of Q if it is
38.68% chlorine by mass and there are twice as many anions as cations in one
formula unit of Q?
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15. A solutioun contains 23.0 grams of an unknown in 100.0 grams of cyclohexane
and boils at a temperature of 87.60°C. The unknown was found to be composed
of 39.1% carbon, 8.69% hydrogen, and 52.2% oxygen by mass. The normal
boiling point and boiling point elevation constant for cyclohexane are 80.72°C
and 2.75°C/m, respectively.
a) Determine the empirical formula of the compound:
b) Calculate the molar mass of the compound:
c) Determine the compound’s molecular formula:
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