Mid-term exam 2, 2004 with answers

# Mid-term exam 2, 2004 with answers - INFORMATION T =...

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INFORMATION T = K b m solute T = K f m solute Π = MRT P soln = X solvent P o solvent P TOTAL = P A + P B X A = (n A + n B ) / n A P = k H X λυ = c E = h υ h = 6.626 x 10 -34 J s c = 3.0 x 10 8 m/s R = 8.3145 J mol -1 s -1 R = 0.08206 L atm mol -1 K -1 1.0 atm = 760 Torr

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1. What is the molality of a solution of 50.0 g of propanol (CH 3 CH 2 CH 2 OH) in 152 mL water, if the density of water is 1.0 g/mL? a) 5.47 m b) 0.00547 m c) 0.833 m d) 0.183 m e) none of these ANS: a) 5.47 m 2. An aqueous solution contains 100.0 g of ethanol (C 2 H 5 OH) in 200.0 g of solution. What is the mole fraction of ethanol? a) 0.281 b) 0.391 c) 0.500 d) 1.00 e) none of these ANS: a) 0.281 3. Which of the following concentration measures will change in value as the temperature of a solution changes? a) mass percent b) mole fraction c) molality d) molarity e) all of these ANS: d) molarity 4. Rank the following compounds according to increasing solubility in water. I. CH 3 –CH 2 –CH 2 –CH 3 II. CH 3 –CH 2 –O–CH 2 –CH 3 III. CH 3 –CH 2 –OH IV. CH 3 –OH a) I < III < IV < II b) I < II < IV < III c) III < IV < II < I d) I < II < III < IV e) No order is correct. ANS: d) I < II < III < IV
5. Solid KF has a lattice energy of 804 kJ/mol and a heat of solution (in water) of –15 kJ/mol. RbF has a lattice energy of 768 kJ/mol and a heat of solution (in water) of –24 kJ/mol. Which salt forms stronger attractions with water? a) KF, since it has a larger lattice energy b) RbF, since it has a smaller lattice energy c) KF, since it has a more negative heat of hydration d) RbF, since it has a more negative heat of hydration e) They form equally strong attractions with water, since they both have negative heats of mixing. ANS: d) RbF, since it has a more negative heat of hydration 6. The solubility of O 2 in water is 0.590 g/L at an oxygen pressure of 15 atm. What is the Henry’s law constant for O 2 (in units of L-atm/mol)? 10 –3 10 –3 10 2 d) 1.26 e) None of the above is within 5% of the correct answer. ANS: c) 2 7. A 50.0 g sample of glucose (a nondissociated, nonvolatile solute with the formula C 6 H 12 O 6 ) is dissolved in 150.0 g water. What is the vapor pressure of this solution at 100 ° C? a) 760 torr b) 25 torr c) 735 torr d) 715 torr e) none of these ANS: c) 735 torr 8. Pentane (C 5 H 12 ) and hexane (C 6 H 14 ) form an ideal solution. The vapor pressures of pentane and hexane at 25 ° C are 511 torr and 150 torr, respectively. The mole fraction of hexane in a pentane-hexane solution is 0.50. Calculate the mole fraction of pentane in the vapor in equilibrium at 25 ° C with this solution. a) 0.23 b) 0.50 c) 0.77 d) 0.89 e) none of these ANS: c) 0.77

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9. A salt solution sits in an open beaker. Assuming constant temperature and pressure, the vapor pressure of the solution a) increases over time. b)
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Mid-term exam 2, 2004 with answers - INFORMATION T =...

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