Chem 142
Exam 2 (Chapters 12 and 14)
Name:________________________________________________
Useful Constants and formulas: R = 8.314 J/mol•K = 0.0821 L•atm/ mol•K
Henry’s Law:
[gas]aq = kHPgas
Freezing Point Depression:
ΔT = i × m × Kf
G   RT n( Kc)
G  G    RT n(Q)
H vap  1 1 
P
n 1   
  
R  T1 T2 
 P2 
b
=
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c d e
= = =
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= = =
= = =
= = =
= = =
= = =
= = =
= = =
= = =
= = =
[13]
[14]
[15]
[16]
[17]
[18]
[19]
[20]
[21]
[22]
[23]
[24]
a
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Osmotic Pressure:
Π = iMRT
ax 2  bx  c  0
PA  X A PA
x
Multiple Choice Darken answer like: = =
a
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[11] =
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Boiling Point Elevation:
ΔT = i × m × Kf
b  b 2  4ac
2a
●=
b
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c d e
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= = =
1 atm = 760 mmHg
Multiple Choice (on your scantron, mark the one best answer for each question below)
1)
Determine the partial pressure of oxygen necessary to form an aqueous solution that is 4.1 × 10 -4 M O2 at
25°C. The Henry's law constant for oxygen in water at 25°C is 1.3 × 10-3 M/atm.
A) 1.9 atm
B) 0.53 atm
C) 0.24 atm
D) 0.77 atm
E) 0.32 atm
2)
Determine the Henry's law constant for ammonia in water at 25°C if an ammonia pressure of 0.022 atm
produces a solution with a concentration of 1.3 M.
A) 59 M/atm
B) 0.017 M/atm
C) 0.029 M/atm
D) 35 M/atm E) 0.038 M/atm
3)
Which of the following should have the largest Henry's law constant (kH) in water? [Hint: remember
intermolecular forces.]
A) Ar
B) CO
C) Xe
D) CH3CH3
E) CO2
4)
Which of the following statements is TRUE?
A) In general, the solubility of a solid in water decreases with increasing temperature.
B) In general, the solubility of a gas in water decreases with increasing temperature.
C) The solubility of a gas in water usually increases with decreasing pressure.
D) Substances with similar intermolecular forces do not like to mix.
E) None of the above statements are true.
5)
A solution is formed at room temperature by dissolving enough of the solid solute so that some solid
remains at the bottom of the solution. Which statement below is TRUE?
A) The solution is considered unsaturated.
B) The solution is considered supersaturated.
C) The solution is considered saturated.
D) The solution would be considered unsaturated if it were cooled a bit to increase the solubility of the
solid.
E) None of the above are true.
6)
Calculate the molality of a solution formed by dissolving 27.8 g of LiI in 500.0 mL of water.
A) 0.254 m
B) 0.394 m
C) 0.556 m
D) 0.241 m
E) 0.415 m
7)
What mass (in g) of NH3 must be dissolved in 475 g of methanol to make a 0.250 m solution?
A) 2.02 g
B) 4.94 g
C) 1.19 g
D) 8.42 g
E) 1.90 g
8)
How many moles of KF are contained in 347 g of water in a 0.175 m KF solution?
A) 1.65 × 10-2 mol KF
B) 5.04 × 10-2 mol KF
C) 6.07 × 10-2 mol KF
D) 3.22 × 10-2 mol KF
-2
E) 1.98 × 10 mol KF
9)
Choose the aqueous solution below with the lowest freezing point. Assume ideal van’t Hoff factors.
A) 0.075 m NaI
B) 0.075 m (NH4)3PO4
C) 0.075 m NaBrO4
D) 0.075 m LiCN
E) 0.075 m KNO2
Page 2 of 8
10)
Choose the aqueous solution that has the highest boiling point. Assume ideal van’t Hoff factors.
A) 0.100 m NaNO3
B) 0.100 m Li2SO4
C) 0.200 m C3H8O3
D) 0.060 m Na3PO4
E) They all have the same boiling point.
11)
An aqueous sucrose (C12H22O11, 342.30 g/mol) solution is made using 500.0 g of water and the boiling point
elevation is found to be 0.39°C. What mass of sucrose was added to the water? Kb of water = 0.512°C/m.
A) 261 g
B) 528 g
C) 762 g
D) 223 g
E) 130. g
12)
Express the equilibrium constant for the following reaction.
2 CH3Cl(g) + Cl2 (g)  2 CH2Cl2 (g) + H2 (g)
A)
B)
D)
K=
[CH3 Cl]2 [Cl2 ]
[CH2 Cl2 ][H2 ]
E)
1
[CH3 Cl][Cl2 ]
K=
[CH2 Cl2 ][H2 ]
13)
C)
[CH2 Cl2 ]2 [H2 ]
K=
[CH3 Cl]2 [Cl2 ]
[CH2 Cl2 ][H2 ]
K=
[CH3 Cl][Cl2 ]
K=
[CH3 Cl]2 [Cl2 ]
1
[CH2 Cl2 ]2 [H2 ]
Express the equilibrium constant for the following reaction:
P4O10(s)  P4(s) + 5 O2(g)
A)
C)
B)
1
[P4 ][O2 ]5
K=
[P4 O10 ]
[P4 O10 ]
K=
[P4 ][O2 ]5
D)
[P4 ][O2 ]5
K=
[P4 O10 ]
E)
1
K=
[O2 ]5
K = [O2 ]5
14) Express the equilibrium constant for the following reaction: Ag2SO4(s) + H2O(l)  2 Ag+(aq) + SO42-(aq)
A)
B)
K=
[Ag + ]2
[SO2−
4
]
K=
[Ag 2 SO4 ] [H2 O]
D)
C)
[Ag 2 SO4 ] [H2 O]
[Ag + ][SO2−
]
4
E)
K=
[SO2−
4
[Ag + ]
]
K = [Ag + ]2 [SO2−
]
4
Page 3 of 8
2
K=
[Ag + ][SO2−
]
4
[H2 O]
15)
The equilibrium constant is given for one of the reactions below. Determine the value of the missing
equilibrium constant.
H2(g) + Br2(g)  2 HBr(g)
Kc = 3.8 × 104
2 HBr(g)  H2(g) + Br2(g)
Kc = ?
A) 1.9 × 104
16)
2 HD(g)  H2(g) + D2(g)
Kc = 0.28
2 H2(g) + 2 D2(g)  4 HD(g)
Kc = ?
D) 6.4 × 10-4
E) 1.6 × 103
B) 3.57
C) 0.529
D) 12.8
E) 1.89
The equilibrium constant is given for one of the reactions below. Determine the value of the missing
equilibrium constant.
2 SO2(g) + O2(g)  2 SO3(g)
Kc = 1.7 × 106
SO3(g)  ½ O2(g) + SO2(g)
Kc = ?
A) 3.4 × 102
18)
C) 2.6 × 10-5
The equilibrium constant is given for one of the reactions below. Determine the value of the missing
equilibrium constant.
A) 7.84 × 10-2
17)
B) 5.3 × 10-5
B) 8.5
C) 1.3 × 103
D) 1.2 × 10-6
E) 7.7 × 10-4
The equilibrium constant is given for two of the reactions below. Determine the value of the missing
equilibrium constant.
A(g) + B(g)  AB(g)
Kc = 0.24
AB(g) + A(g)  A2B(g)
Kc = 3.8
2 A(g) + B(g)  A2B(g)
Kc = ?
A) 4.0
B) 0.91
C) 3.6
D) 16
E) 0.63
19) Determine the value of Kc for the following reaction if the equilibrium concentrations are as follows:
[N2]eq = 1.5 M, [H2]eq = 1.1 M, [NH3]eq = 0.47 M.
N2 (g) + 3 H2(g)  2 NH3(g)
A) 3.5
B) 0.28
C) 9.1
D) 0.11
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E) 0.78
20)
Consider the following reaction and its equilibrium constant:
SO2(g) + NO2(g)  SO3(g) + NO(g)
Kc = 0.33
A reaction mixture contains 0.43 M SO2, 0.14 M NO2 , 0.11 M SO3 and 0.14 M NO. Which of the
following statements is TRUE concerning this system?
A) The reaction will shift in the direction of reactants.
B) The equilibrium constant will decrease.
C) The reaction will shift in the direction of products.
D) The reaction quotient will decrease.
E) The system is at equilibrium.
21) Consider the following reaction and its equilibrium constant:
I2(g) + Br2(g)  2 IBr(g)
Kc = 1.1 × 102
A reaction mixture contains 0.41 M I2, 0.27 M Br2 and 3.5 M IBr. Which of the following statements is
TRUE concerning this system?
A) The reaction will shift in the direction of products.
B) The reaction will shift in the direction of reactants.
C) The reaction quotient will decrease.
D) The equilibrium constant will increase.
E) The system is at equilibrium.
22) Which of the following statements is FALSE?
A) When K >> 1, the forward reaction is favored and essentially goes to completion.
B) When K << 1, the reverse reaction is favored and the forward reaction does not proceed to a great
extent.
C) When K ≈ 1, neither the forward or reverse reaction is strongly favored, and about the same amount of
reactants and products exist at equilibrium.
D) When Q = K, the system is at equilibrium and the forward and reverse reactions stop.
E) When Q is much greater than K, the reaction will shift left to increase the amount of reactants.
23) Warming the water will increase the solubility of which of the following?
A) CaCl2, which produces heat when it dissolves in water.
B) NH4NO3, which cools when it dissolves in water.
C) CO2 gas
D) ethanol
E) all the above
24) The reaction ClCOCl(g) = Cl2(g) + CO(g) has reached equilibrium in a reaction vessel. Which of the
following is correct?
A) Increasing the pressure decreases the Kp.
B) Increasing the pressure shifts the reaction to the right.
C) Adding an inert gas shifts the equilibrium to the left.
D) Changing the temperature has no effect on Kp.
E) Decreasing the volume shifts the equilibrium to the left.
Page 5 of 8
Calculation / Short answer section. Write your answers, with correct sig figs and units, in the space provided. Show all work for maximum credit.
23)
Review your answer to question 22 in the multiple choice section. Rewrite the false statement below, to
make a correct statement. (4 pts)
24)
At your new job, your boss asks you to make 1.500 liters of an aqueous solution of glucose (C6H12O2) that
is 1.52 % by mass. Assume the density of the final solution will be 0.998 g/mL.
a)
How many grams of glucose do you need? (6 pts)
b)
What is the molarity of this solution? (The molar mass of glucose is 116.15 g/mol)
(5 pts)
c)
What is the molality of the solution?
(5 pts)
25)a Determine the freezing point of a solution that contains 78.8 g of naphthalene (C10H8, molar mass = 128.16
g/mol) dissolved in 722 mL of benzene (density = 0.877 g/mL). Pure benzene has a melting point of
5.50°C and a freezing point depression constant of 4.90°C/m. (8 pts)
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b. What are the partial pressures of benzene and naphthalene above this solution, given the vapor pressures for
the pure substances at the same temperature given below?
Naphthalene
Benzene
26)
P°
.082 mmHg
0.1252 atm
a) What is the ideal van’t Hoff factor for (NH4)2SO4? (2 pts)
b) The boiling point of an aqueous 1.83 m (NH4)2SO4 solution is 102.5 °C. Determine the actual value of
the van't Hoff factor for this solute. The Kb for water is 0.512°C/m and the boiling point of pure water is
100.0 °C. (4 pts)
27)
Consider the following reaction. The equilibrium concentration of NH3 was found to be 2.9 × 10-3 M.
Determine the equilibrium concentration of CO2(g). (6 pts)
NH2COONH4(s)  2 NH3(g) + CO2(g)
Page 7 of 8
Kc = 1.58 × 10-8
28)
Consider the following reaction:
COCl2(g)  CO(g) + Cl2(g)
A reaction mixture initially contains only 1.6 M COCl2. Determine the equilibrium concentration of CO if
Kc for the reaction at this temperature is 8.33 × 10-4. (8 pts)
At what temperature was this equilibrium constant determined? Gibbs Free energy data are provided below;
assume they are constant over the range of temperatures for this problem.
PCl5 (g)
PCl3 (g)
Cl2 (g)
ΔG° (kJ/mol)
-305.0
-267.8
0
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