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Exam
Name___________________________________
MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.
1) Which one of the following substances would be the most soluble in CCl4 ?
1)
A) H2 O
B) NaCl
C) C10H22
D) NH3
E) CH3CH2OH
2) Calculate the molarity of a 25.4% (by mass) aqueous solution of phosphoric acid (H3 PO4 ).
2)
3) Which one of the following concentration units varies with temperature?
A) mass percent
B) molality
C) molarity
D) mole fraction
E) all of the above
3)
4) Which of the following liquids will have the lowest freezing point?
A) pure H2 O
4)
A) 3.47 m
B) 4.45 m
C) 2.59 m
D) 25.4 m
E) The density of the solution is needed to solve the problem.
B) aqueous KF (0.50 m)
C) aqueous sucrose (0.60 m)
D) aqueous FeI3 (0.24 m)
E) aqueous glucose (0.60 m)
5) Colligative properties of solutions include all of the following except __________.
A) depression of vapor pressure upon addition of a solute to a solvent
B) depression of the freezing point of a solution upon addition of a solute to a solvent
C) the increase of reaction rates with increase in temperature
D) elevation of the boiling point of a solution upon addition of a solute to a solvent
E) an increase in the osmotic pressure of a solution upon the addition of more solute
5)
6) Of the following, all are valid units for a reaction rate except __________.
A) g/s
B) mol/L-hr
C) mol/L
D) M/s
6)
1
E) mol/hr
7) At elevated temperatures, dinitrogen pentoxide decomposes to nitrogen dioxide and oxygen:
2N2O5 (g)
7)
4NO 2 (g) + O2 (g)
When the rate of formation of O2 is 2.2 × 10-4 M/s, the rate of decomposition of N2 O5 is
__________ M/s.
A) 1.1 × 10-4
B) 4.4 × 10-4
C) 2.8 × 10-4
D) 5.5 × 10-4
E) 2.2 × 10-4
8) The rate law of a reaction is rate = k[D][X]. The units of the rate constant are __________.
A) mol2 L-2s-1
8)
B) mol L-1 s-2
C) L mol-1 s-1
D) mol L-1 s-1
E) L2 mol-2s-1
The data in the table below were obtained for the reaction:
2 ClO2 (aq) + 2 OH- (aq)
ClO3 - (aq) + ClO2 - (aq) + H2O (1)
Experiment
Initial Rate
Number [ClO2 ] (M) [OH- ] (M)
(M/s)
1
0.060
0.030
0.0248
2
0.020
0.030
0.00276
3
0.020
0.090
0.00828
9) What is the order of the reaction with respect to OH- ?
A) 0
B) 1
C) 2
D) 3
9)
E) 4
10) As the temperature of a reaction is increased, the rate of the reaction increases because the
__________.
A) reactant molecules collide less frequently
B) reactant molecules collide more frequently with less energy per collision
C) reactant molecules collide less frequently and with greater energy per collision
D) reactant molecules collide more frequently and with greater energy per collision
E) activation energy is lowered
10)
11) What is the molality (m) of a solution of 31.8 g of ethanol (CH3 CH2 OH molar mass 46 g/mol) in
481 mL of water if the density of water is 1.0 g/mL?
11)
A)
1.44
m
B)
1.35
m
C)
0.025
2
8
m
D)
0.025
2
m
E)
66.1
m
12) A possible mechanism for the overall reaction
Br2 (g) + 2NO (g)
is
NO (g) + Br2 (g)
12)
2NOBr (g)
k1
k -1
NOBr2 (g) + NO (g)
NOBr2 (g)
k2
2NOBr
(fast)
(slow)
The rate law for formation of NOBr based on this mechanism is rate = __________.
A) k1 [Br2 ]1/2
B) (k1 /k-1 )2[NO]2
C) k1 [NO]1/2
D) (k2 k1 /k-1 )[NO][Br2 ]2
E) (k2k1 /k-1)[NO]2 [Br2 ]
13) Calculate the freezing point (0°C) of a 0.05500 m aqueous solution of NaCl. The molal
freezing-point-depression constant of water is 1.86 °C/m.
A) -0.2046
B) -0.1023
C) -0.05627
D) 0.1023
E) 0.0286
13)
14) Which energy difference in the energy profile below corresponds to the activation energy for the
forward reaction?
14)
A) x
B) y
C) x - y
D) y - x
ESSAY. Write your answer in the space provided or on a separate sheet of paper.
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E) x + y
15) The decomposition of a certain insecticide in water at 12 oC follows first-order kinetics with a rate constant of
1.45 /yr.
a.
A quantity of this insecticide is washed into a lake on June 1, leading to a concentration of 5.0 x 10-7
g/cm3 . Assume that the average temperature of the lake is 12 oC. (a) What is the concentration of the
insecticide on June 1 after 1 year?
(b) How long will it take for the insecticide concentration to decrease to 3.0 x 10—7 g/cm3 ?
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16) (a)Consider a 2m solution of sugar in water at 25oC. What is the value of the mole fraction of water in this
solution? [Hint: Imagine that the solution was made up with exactly 1.00 Kg of water.] (m.w. H2O = 18.02 u)
(b) Calculate the vapor pressure above a 2m solution of sugar in water at 25oC, given that the vapor pressure of
pure water at this temperature is 23.77 mm Hg
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