Name: ________________________
Hour: ____ Date: ___________
AP Chemistry: 13HW
Directions: Complete the following problems.
Would you use water or carbon tetrachloride to dissolve each of the following?
1A.
xenon difluoride
1B.
sodium chloride
sulfur dichloride
methanal (CH2O)
sulfur dioxide
ethene (H2C=CH2)
carbon dioxide
hydrogen bromide
For each pair, circle the substance that would be more soluble in water.
2A.
CH3OH or CH3CH3
CHF3 or CF4
2B.
CH3CH2OH or CH3(CH2)5OH
heptane (C7H14) or (NH4)3PO4
3A. At 25oC, the solubility of oxygen in water is 2.86 x 10–4 M when the partial pressure of the oxygen above the
water is 0.210 atm. Determine the Henry’s law constant for oxygen at 25oC and also the solubility of
oxygen when its partial pressure above the water is 3.10 atm.
3B. The Henry’s law constant for helium is 3.58 x 10–4 M/atm at 25oC. Determine the partial pressure of helium
above a water solution if there are 0.0103 g of helium dissolved in a solution of volume 941 mL?
ANSWERS:
3A. 1.36 x 10–3 M/atm; 4.22 x 10–3 M
3B. 7.64 atm
4A. A 35.0-mL water sample is found to contain 8.2 x 10–8 g of lead. Determine the presence of lead in ppb.
4B. Arsenic is found in a 5.0-L sample of pond water in a proportion of 1.23 ppm. If the pond contains
approximately 2,500 m3 of water, estimate the total mass of arsenic in the pond.
5A. A phosphoric acid solution was made by dissolving 12.5 g of solute in 125 mL of water. The resulting
solution’s volume was 130. mL. Determine the solution’s density, mole fraction, molarity, and molality.
5B. An aqueous antifreeze solution is 50.0% ethylene glycol (C2H6O2) by mass and has a density of 1.07 g/mL.
Determine the molality, molarity, and mole fraction of the ethylene glycol.
ANSWERS:
4A. 2.3 ppb
4B. 3100 g
5A. 1.06 g/mL; X = 0.0180; 0.982 M; 1.02 m
5B. 16.1 m; 8.63 M; X = 0.225
5C. A solution contains 35 mL of pentane (C5H12, D = 0.63 g/mL) and 65 mL of heptane (C7H16, D = 0.68 g/mL).
Assuming additive volumes, find the mass percent, mole fraction, molality, and molarity of the pentane.
6A. A 39.8oC aqueous solution has a vapor pressure (VP) of 47 torr. The solution contains 63.4 g of the
nonvolatile, nondissociating liquid glycerin (C3H8O3) and 73.7 g of water. Find the VP of water at 39.8oC.
6B. Find the VP of a 40.0oC solution containing 146 g of the nonvolatile, nonelectrolyte urea ((NH2)2CO) and
385 mL of ethanol (CH3CH2OH). Ethanol’s VP at 40.0oC is 136 torr; its density is 0.789 g/mL.
ANSWERS:
5C. 33%; X = 0.41; 6.9 m; 3.1 M
6A. 54 torr
6B. 91.3 torr
6C. At 64oC, the VP of 1,2-dichloroethane (C2H4Cl2) is 0.526 atm. At that temperature, a solution was made
using 13.2 of a nonvolatile, nondissociating solute and 138.5 g of C2H4Cl2. The solution’s VP was found
to be 0.472 atm. Determine the molar mass of the solute.
7A. A solution has 22.0 mL of heptane (C7H16, D = 0.680 g/mL) and 75.0 mL of hexane (C6H14, D = 0.660 g/mL).
At 50oC, assume that their VPs are 150. and 400. torr, respectively. Find the solution’s VP at 50oC.
7B. A sealed vessel contains a mixture of 956 g of trichloromethane (CHCl3, also called chloroform) and 230. g
of ethanol (CH3CH2OH). At 30oC, assume that their vapor pressures are 36.0 kPa and 13.0 kPa,
respectively. Find the composition of the vapor above the solution, in terms of mole fractions, at 30oC.
ANSWERS:
6C. 82.5 g
7A. 348 torr
7B. XCHCl3 = 0.816, Xethanol = 0.184
8A. A solution contains 72.0 g of the nonelectrolyte glycerin, C3H8O3, in 180.0 g of water. Find its boiling point.
8B. What mass of the nonelectrolyte urea, (NH2)2CO, must be dissolved in 250. g of water to give a solution with
a freezing point of –3.25oC?
8C. The freezing point of 1,4-dichlorobenzene (i.e., para-dichlorobenzene) is 53.5oC; its Kf is 7.1oC/m. What
mass of sodium chloride is in a 42.0-g sample of 1,4-dichlorobenzene, if the mixture freezes at 47.9oC?
9A. A 3.50-g sample of an enzyme is dissolved in 21.0 g of carbon tetrachloride. The mixture’s BP is 79.25oC.
The Kb for carbon tetrachloride is 5.03oC/m and its NBP is 76.50oC. Find the enzyme’s molar mass.
9B. Testosterone is a natural steroid responsible for, among other things, muscle growth in males. If 0.515 g of
testosterone are dissolved in 15.0 g of benzene (Kf = 5.12oC/m), the freezing point drops by 0.610oC.
Determine the molar mass of testosterone.
ANSWERS:
8A. 102.26oC
8B. 26.2 g
8C. 1.94 g
9A. 305 g
9B. 288 g
9C. Estradiol, the predominant estrogen during a female’s reproductive years, has the empirical formula C9H12O.
When 1.12 g of estradiol is dissolved in 11.2 g of camphor (Kf = 40.oC/m, MP = 176.0oC), the mixture
freezes at 161.3oC. Find the molecular formula of estradiol.
10A. A 27oC aqueous solution contains 7.5 g of the enzyme catalase per liter. Assuming catalase’s molar mass
to be 2.5 x 105 g and the solution’s density to be that of water, find the osmotic pressure, in torr.
10B. An aqueous solution contains 12.25 g of a protein in a total volume of 425 mL. The solution’s osmotic
pressure is 1.34 torr at 22oC. Determine the protein’s molar mass.
Use the available choices to answer each question. Solutions are aqueous, unless otherwise noted.
11A.
choices:
X conc. MgCl2 X conc. K3PO4
X conc. NaBr X conc. HF
11B.
choices:
X conc. C12H22O11
X conc. LiF
has same BP as 2X conc. C6H12O6
has highest FP
has highest VP at 28oC
has lowest FP
has largest FP depression
has highest BP
has smallest BP elevation
has lowest BP
has largest osmotic pressure
has largest osmotic pressure
ANSWERS:
9C. C18H24O2
10A. 0.56 torr
10B. 3.96 x 105 g
pure water
X conc. CaBr2