Houston Community college System
Chemistry 1412
Exam # 1
Summer 2012
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CHEM 1412 Exam #1
Summer 2012
Name: ____________________________
Score:
PART I - ( 3 points each) - Please write your correct answer next to each question number. DO NOT
CIRCLE.
___1. Calculate the molality of a 3.62% by mass aqueous solution of sodium hypochlorite, NaOCl (molar mass
= 74.43 g/mol)?
A. 0.505 m
B. 0.0486 m
C. 0.584 m
D. 0.486 m
E. 2.25 m
___2. What is the molarity of a solution containing 25.0 g NaCl and 75.0 g H2O if the density of the solution is
1.20 g/mL?
A. 6.84 M
B. 3.56 M
C. 4.75 M
D. 5.13 M
E. 5.70 M
___3. Which of the following is least likely to participate in hydrogen bonding?
A. H2O
B. CH3OH
C. NH3
D. CH3NH2
E. C6H6
___4. Which of the following happens when NaCl is dissolved in water?
A. Vapor Pressure of increases
D. freezing point increases
B. Boiling point increases
E. Melting point increases
C. water dissociates
___ 5. Which one of the following 0.15 m aqueous solutions should have the highest boiling point?
A. NH2CONH2
B. NH4Cl
C. CaCl2
D. Na3PO4
E. HNO3
____6. The reaction A + B → products was found to have the rate law, rate = k[B]2. Predict by what factor the
rate of reaction will increase when the concentration of A is tripled
A. 3
B.6
C. 9
D. 18
E. unchanged
___7. Pure benzene freezes at 5.48°C. The freezing point depression constant of benzene is 5.12 °C/m.
Estimate the freezing point of the solution formed by dissolving 0.120 moles of naphthalene, C10H8, in
78.0 g of benzene.
A. 5.48 °C
B. 7.88 °C
C. -2.40 °C
D. 13.4 °C
E. 121 °C
___8. The vapor pressure of pure water at 50°C is 92.5 torr. What is the vapor pressure of the aqueous
solution prepared by dissolving 1.00 mol Na2CO3 in 10.0 mol H2O?
A. 8.41 torr
B. 84.1 torr
C. 21.3 torr
D. 71.3 torr
E. 120 torr
____9. The normal boiling point of pure cyclohexane is 80.7°C. The boiling point elevation constant of
cyclohexane is 2.79 °C/m. Estimate the boiling point of the solution formed by dissolving 0.200 moles
of a molecular solute in 500.0g of cyclohexane.
A. 79.6 °C
B. 81.8 °C
C. 81.0 °C
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D. 80.4 °C
E. 87.7 °C
____10. If the overall order of a reaction= 1/3, the unit for the rate constant is ………
A. M1/3s-1
B. M-1/3s-1
C. M2/3s-1
D. M-2/3s-1
E. Ms-1
___11. For the reaction A + 2B → C + 3D at a particular time, -Δ[B]/Δt = 6.2 M/s.
What is Δ[C]/Δt at the same instant?
A. 2.1 M/s
B. 12.4 M/s
C. 3.1 M/s
D. 9.3 M/s
E. 6.2 M/s
___12. The half-life of a first order reaction is 10.0 s when the initial reactant concentration is 1.00M. What will be the halflife if 0.500 M initial reactant concentration had been taken?
A. 5.00 s
B. 10.0 s
C. 20.0 s
D. 0.050 s
E. Cannot determine
___13. The reaction Aproducts has the rate law, rate = k[A]2. If the rate of the reaction is 0.47 Ms-1 when the
concentration [A] is 0.30 M, what is the value of the rate constant for this reaction?
A. 0.042M-1s-1
B. 0.066M-1s-1
C. 5.2M-1s-1
D. 0.19M-1s-1
E. 0.74M-1s-1
___14. The values of equilibrium constants are affected by which of the following:
A. Temperature changes
D. Pressure changes
_____15.
B. Volume changes
E. All of them
C. presence of a catalyst
Calculate Kp for the following reaction: H2(g) + CO2(g)
A. 11.82
B. 0.0846
C. 1.95 x 104
H2O(g) + CO(g) if Kc = 11.82
D. 1
E. 0
_____16. Consider the equilibrium, H2(g) + I2(g)
2HI(g). If the equilibrium constant, Kp, is 54 and the
equilibrium partial pressures of H2 is 0.147 atm and that of HI is 2.69 atm, calculate the equilibrium partial
pressure of I2.
A. 7.35 atm
B. 0.912 atm
C. 0.678 atm
D. 1.10 atm
E. 1.48 atm
_____17. For the following reaction system at equilibrium, which one of the changes would cause the equilibrium
to shift to the right?
2A(g) +B(g)
A. Increase in container volume
D. Increase in Temperature
∆Hº = -250 kJ
C(g) + D(g)
B. Removing A
E. Increase the partial pressure of B
C. Introduction of a Catalyst
_____18. Consider the equilibrium 2X(s) + Y(g)  2Z(g), KC = 100. What is the equilibrium constant, KC
For the equilibrium, Z(g)  X(s) + (1/2)Y(g)
A. 10
B. 0.10
C. 50
D. 0.02
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E. 0.005
_____19. Peroxodisulfate ion can oxidize iodide ions to iodine according to the balanced equation
S2O82– + 2I – → 2SO42– + I2.
The reaction is catalyzed by certain chemical species. Identify the catalyst in the following mechanism:
step 1: Fe3+ + 2I – → Fe2+ + I2
step 2: S2O82– + Fe2+ → 2SO42– + Fe3+
A. Fe+3
B. I-
C. Fe+2
D. I2
E. S2O8-2
_____20. If 0.035 moles of SO2, 0.500 moles of SO2Cl2, and 0.080 moles of Cl2 are combined in a 5.00 L flask
Which of the following statements is true?
SO2Cl2(g)
SO2(g) + Cl2(g)
Kc = 0.078 at 100oC
A. The system is at equilibrium, thus no concentration changes will occur.
B. The concentrations of SO2 and Cl2 will increase as the system approaches equilibrium.
C. The concentration of SO2Cl2 will increase as the system approaches equilibrium.
Part II- Please show all your work for full credit. (8 points each)
21. A certain reaction A products has the rate law: rate = k[A]. If the initial concentration of A is 1.00M and
the concentration of A after 50 s is 0.677, calculate the following:
a.
b.
22.
The rate constant for the reaction
The half-life of the reaction
The osmotic pressure of a100 mL aqueous solution containing 1.00 g of caffeine is 1130 torr at 80.0°C.
Calculate the molar mass of caffeine?
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The following data were collected for the reaction 2A + B  Products:
Exp.
[A] mol/L
[B] mol/L
-∆[A]/∆t (M/s)
1
0.105
0.150
1.8 x 10-5
2
0.105
0.300
7.2 x 10-5
3
0.052
0.300
3.6 x 10-5
Calculate:
a) the rate law expression;
b) the rate constant (include units)
c) the rate of consumption of A when [A] = 0.200 M, [B] = 0.200 M
23.
24.
Initially, the partial pressure of N2O4(g) is 3.00 atm and that of NO2(g) is 2.00 atm. The following
equilibrium is established: 2NO2(g)
N2O4(g). If the equilibrium partial pressure of NO2(g) is 1.05
atm, calculate the equilibrium constant, Kp.
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25.
The rate constant of a first-order reaction is 1.20x10-2min-1 at 379C. If the activation energy is
218kJ/mol, calculate the rate constant at 272C.
Bonus: Consider the equilibrium HA(aq) +H2O(l)
A-(aq) + H3O+(aq). If the equilibrium constant Kc is
10000, and the initial concentration of HA is 1.00 M, calculate the equilibrium concentrations of HA, A- & H3O+.
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