Chemistry 1304.001
Exam 2 (100 points)
Name (please print CLEARLY)
February 24, 2016
On my honor, I have neither given nor received unauthorized aid on this exam.
Signed
Date
1. (3 points) Which solution will have the lowest pH? (Please discretely circle only the letter of your answer here and in #2.)
a. 0.10 M NaOH
b. 0.10 M Ba(OH)2
c. 0.10 M HCN
d. 0.10 M NaCl
e. 0.10 M HNO3
f. all will have the same pH
2. (4 points) For the reaction H2 (g) + I2 (g)
2 HI (g), Kc = 0.52 at a certain temperature. If the
concentrations are H2 = 0.40 M, I2 = 0.40 M , HI = 0.40 M, which of the following is true?
a. The system is at equilibrium and no concentrations changes will occur.
b. The concentration of HI and I2 will increase as the system approaches equilibrium.
c.
The concentrations of HI and I2 will decrease as the system approaches equilibrium.
d.
The concentration of HI will increase as the system approaches equilibrium.
e.
The concentrations of H2 will increase as the system approaches equilibrium.
f.
None of the above is true.
3. (6 points) Fill in the missing information in the following table.
Solute
Molarity
NaBr
4.6 M
–
[OH ]
HCl
pH
pOH
– 0.7
4. (4 points) If a 0.055 M solution of the weak acid CH3COOH is 3.3% ionized, the pH of the solution is
and the conjugate acid of HCO3– is
5. (4 points)The conjugate base of HNO2 is
6. (8 points) Label each of the following aqueous solutions as acidic (A), a basic (B), or neutral (N).
RbF
(CH3)2NH
KNO3
CH3CH2COOH
7. (2 points) Nitrous oxide (N2O) decomposes at 600 °C according to the balanced equation
2 N2O (g) → 2 N2 (g)
+
O2 (g) .
A reaction mechanism involving three steps is shown below.
The catalyst(s) in this mechanism is(are)
Cl2 (g) → 2 Cl (g)
N2O (g) + Cl (g) → N2 (g) + ClO (g) (occurs twice)
ClO (g) + ClO (g) → Cl2 (g) + O2 (g)
8. (6 points) If the Kb of NH3 is 1.8 x 10-5, what is the pH of a 0.75 M aqueous solution of NH3? SHOW
REACTION and WORK.
.
page 2
9.
(8 points)
(aq) Write the equilibrium reaction (including states) for an aqueous solution of each of the following,
and note which equilibrium constant (Ka, Kb, Kc, Kp, Kw etc.) applies. (You don't need the entire expression.)
CsBrO2
CH3NH3Cl
10. Coal can be used to produce hydrogen (a potential fuel) by the following reaction (∆H° = 90 kJ).
C (s) + 2 H2O (g)
CO2 (g) + 2 H2 (g)
At equilibrium, how will the molar
concentration of H2(g) and/or the value of Kc be
affected by each of following changes? Indicate
your answers by writing the appropriate letter.
Change
(10 points)
[H2]
increase the pressure
add more coal, C (s)
increase the temperature
[I = increase, D = decrease, N = no change]
add a catalyst
remove some CO2 (g)
11. Consider the following reaction in terms of kinetics and mechanism. The answers to part a and part b are
unrelated, so you can answer one question without the other.
N2O5 + O2 →
N2O + 2 O3
a. (3 points) Could this reaction possibly occur by a simple one-step mechanism? Briefly explain (in 30
words or less!) your answer and predict the rate law for the reaction if it did occur in one-step.
b.
(7 points) There is experimental evidence for the possible existence of N2O2 as an intermediate in the
above reaction.
a. Propose a reasonable two-step mechanism for this reaction that is consistent with this
observation.
b. Now derive the predicted rate law, if the second step in this mechanism is the rate-determining
step. (Note: Use symbols like k1, k-1, and k2 for rate constants where appropriate.)
page 3
12. (8 points) A reaction vessel at 100 °C initially contains a mixture of SO2 (P = 0.50 atm) and O2 (P = 0.20 atm).
The following reaction occurs and, at equilibrium, the total pressure is 0.625 atm. Determine the value of Kp
for this reaction. CLEARLY SHOW ALL WORK!
2 SO2 (g)
+
O2 (g)
2 SO3 (g)
13. (8 points) What mass of sodium formate (HCOONa, molar mass, 68.0) must be added to 500.0 mL of water in
order to obtain a solution having a pH of 7.90? [Ka (HCOOH) = 1.8 × 10-4] . CLEARLY STATE and
EXPLAIN ANY ASSUMPTIONS that you make and SHOW ALL WORK. You must write the chemical
reaction.
14. (8 points) Hydrogen, a potential fuel, is found in great abundance in water. Before the hydrogen can be used
as a fuel, however, it must be separated from the oxygen, i.e., the water must be split into H2 and O2. One
possibility is thermal decomposition, but this requires very high temperatures. Even at 1000 °C,
Kc = 7.3 x 10-18 for the reaction. If at 1000 °C, the H2O concentration in a reaction vessel is set initially at
2.50 M, what will the H2 concentration be when the reaction reaches equilibrium? CLEARLY STATE and
EXPLAIN ANY ASSUMPTIONS that you make and SHOW ALL WORK!
2 H2O (g)
2 H2 (g) + O2 (g)
page 4
15. One of the ways to make essentially insoluble ionic compounds dissolve is to form more soluble complex
ions that pull the one of the insoluble ions into solution. This can be applied to make Cu3(PO4)2 (s) as
shown in the following reaction.
Cu3(PO4)2 (s) + 12 CN– (aq)
2 PO43– (aq) + 3 Cu(CN)42- (aq)
a. (3 points) Write the equilibrium constant expression, Kc, for this reaction.
b. (8 points) Using the following information, determine the value of the equilibrium constant for the reaction
above. SHOW ALL WORK CLEARLY.
3 Cu2+ (aq) + 2 PO43– (aq)
K' = 1.4 x 10-37
Cu3(PO4)2 (s)
Cu2+ (aq) + 4 CN– (aq)
Cu(CN)42K" = 1.0 x 1029
c.
(Extra credit: 5 points) If the initial concentration of CN– is 1.20 M, what is the final concentration of CN–,
PO43–, and Cu(CN)42–? CLEARLY STATE and EXPLAIN ANY ASSUMPTIONS that you make and
SHOW ALL WORK!
Chemistry 1304.001
Exam 2 (100 points)
Name (please print CLEARLY)
February 24, 2016
On my honor, I have neither given nor received unauthorized aid on this exam.
Signed
Date
1. (3 points) Which solution will have the lowest pH? (Please discretely circle only the letter of your answer here and in #2.)
a. 0.10 M NaOH
b. 0.10 M Ba(OH)2
c. 0.10 M HCN
d. 0.10 M NaCl
e. 0.10 M HNO3
f. all will have the same pH
2. (4 points) For the reaction H2 (g) + I2 (g)
2 HI (g), Kc = 0.52 at a certain temperature. If the
concentrations are H2 = 0.40 M, I2 = 0.40 M , HI = 0.40 M, which of the following is true?
a. The system is at equilibrium and no concentrations changes will occur.
b. The concentration of HI and I2 will increase as the system approaches equilibrium.
c.
The concentrations of HI and I2 will decrease as the system approaches equilibrium.
d.
The concentration of HI will increase as the system approaches equilibrium.
e.
The concentrations of H2 will increase as the system approaches equilibrium.
f.
None of the above is true.
3. (6 points) Fill in the missing information in the following table.
Solute
Molarity
NaBr
4.6 M
–
[OH ]
HCl
pH
pOH
– 0.7
4. (4 points) If a 0.055 M solution of the weak acid CH3COOH is 3.3% ionized, the pH of the solution is
and the conjugate acid of HCO3– is
5. (4 points)The conjugate base of HNO2 is
6. (8 points) Label each of the following aqueous solutions as acidic (A), a basic (B), or neutral (N).
RbF
(CH3)2NH
KNO3
CH3CH2COOH
7. (2 points) Nitrous oxide (N2O) decomposes at 600 °C according to the balanced equation
2 N2O (g) → 2 N2 (g)
+
O2 (g) .
A reaction mechanism involving three steps is shown below.
The catalyst(s) in this mechanism is(are)
Cl2 (g) → 2 Cl (g)
N2O (g) + Cl (g) → N2 (g) + ClO (g) (occurs twice)
ClO (g) + ClO (g) → Cl2 (g) + O2 (g)
8. (6 points) If the Kb of NH3 is 1.8 x 10-5, what is the pH of a 0.75 M aqueous solution of NH3? SHOW
REACTION and WORK.
.
page 2
9.
(8 points)
(aq) Write the equilibrium reaction (including states) for an aqueous solution of each of the following,
and note which equilibrium constant (Ka, Kb, Kc, Kp, Kw etc.) applies. (You don't need the entire expression.)
CsBrO2
CH3NH3Cl
10. Coal can be used to produce hydrogen (a potential fuel) by the following reaction (∆H° = 90 kJ).
C (s) + 2 H2O (g)
CO2 (g) + 2 H2 (g)
At equilibrium, how will the molar
concentration of H2(g) and/or the value of Kc be
affected by each of following changes? Indicate
your answers by writing the appropriate letter.
Change
(10 points)
[H2]
increase the pressure
add more coal, C (s)
increase the temperature
[I = increase, D = decrease, N = no change]
add a catalyst
remove some CO2 (g)
11. Consider the following reaction in terms of kinetics and mechanism. The answers to part a and part b are
unrelated, so you can answer one question without the other.
N2O5 + O2 →
N2O + 2 O3
a. (3 points) Could this reaction possibly occur by a simple one-step mechanism? Briefly explain (in 30
words or less!) your answer and predict the rate law for the reaction if it did occur in one-step.
b.
(7 points) There is experimental evidence for the possible existence of N2O2 as an intermediate in the
above reaction.
a. Propose a reasonable two-step mechanism for this reaction that is consistent with this
observation.
b. Now derive the predicted rate law, if the second step in this mechanism is the rate-determining
step. (Note: Use symbols like k1, k-1, and k2 for rate constants where appropriate.)
page 3
12. (8 points) A reaction vessel at 100 °C initially contains a mixture of SO2 (P = 0.50 atm) and O2 (P = 0.20 atm).
The following reaction occurs and, at equilibrium, the total pressure is 0.625 atm. Determine the value of Kp
for this reaction. CLEARLY SHOW ALL WORK!
2 SO2 (g)
+
O2 (g)
2 SO3 (g)
13. (8 points) What mass of sodium formate (HCOONa, molar mass, 68.0) must be added to 500.0 mL of water in
order to obtain a solution having a pH of 7.90? [Ka (HCOOH) = 1.8 × 10-4] . CLEARLY STATE and
EXPLAIN ANY ASSUMPTIONS that you make and SHOW ALL WORK. You must write the chemical
reaction.
14. (8 points) Hydrogen, a potential fuel, is found in great abundance in water. Before the hydrogen can be used
as a fuel, however, it must be separated from the oxygen, i.e., the water must be split into H2 and O2. One
possibility is thermal decomposition, but this requires very high temperatures. Even at 1000 °C,
Kc = 7.3 x 10-18 for the reaction. If at 1000 °C, the H2O concentration in a reaction vessel is set initially at
2.50 M, what will the H2 concentration be when the reaction reaches equilibrium? CLEARLY STATE and
EXPLAIN ANY ASSUMPTIONS that you make and SHOW ALL WORK!
2 H2O (g)
2 H2 (g) + O2 (g)
page 4
15. One of the ways to make essentially insoluble ionic compounds dissolve is to form more soluble complex
ions that pull the one of the insoluble ions into solution. This can be applied to make Cu3(PO4)2 (s) as
shown in the following reaction.
Cu3(PO4)2 (s) + 12 CN– (aq)
2 PO43– (aq) + 3 Cu(CN)42- (aq)
a. (3 points) Write the equilibrium constant expression, Kc, for this reaction.
b. (8 points) Using the following information, determine the value of the equilibrium constant for the reaction
above. SHOW ALL WORK CLEARLY.
3 Cu2+ (aq) + 2 PO43– (aq)
K' = 1.4 x 10-37
Cu3(PO4)2 (s)
Cu2+ (aq) + 4 CN– (aq)
Cu(CN)42K" = 1.0 x 1029
c.
(Extra credit: 5 points) If the initial concentration of CN– is 1.20 M, what is the final concentration of CN–,
PO43–, and Cu(CN)42–? CLEARLY STATE and EXPLAIN ANY ASSUMPTIONS that you make and
SHOW ALL WORK!