Chem 112
Question 1
6 Points
Question 2
8 Points
Question 3
6 Points
Question 4
4 Points
Spring 2008
Exam II – Key
Write the equilibrium constant expression, Kc, for the following reactions:
A. MnS(s)
Ù Mn2+(aq) + S2-(aq)
Kc = [Mn2+][S2-]
B. 2 NOBr(g)
Ù 2 NO(g) + Br2(g)
Kc = [NO]2[Br2]/[NOBr]2
CO(g) + Cl2(g) Ù COCl2(g), Kc=77.5 at 600K. Assuming you start with equal concentrations
of CO(g) and Cl2(g) and no COCl2(g), at equilibrium:
A. [COCl2]
1
1. Will be higher
B. [Cl2]
4
2. Impossible to tell
C. [CO]
4
3. Will be the same
D. Kc relative to Kp
1
4. Will be lower
Consider the following reaction where Kp = 0.365 at 1150 K:
2 SO2(g) + O2(g) Ù 2 SO3(g)
If the three gases are mixed in a rigid container at 1150 K so that the partial pressure of
each gas is initially one atm, what will happen?
Indicate True (T) False (F), or Impossible to Tell (I) for each of the following:
A. Q is greater than K
T
D. More SO3 will be produced.
F
B. No reaction will occur
F
E. Kp will increase
F
C. Reaction is endothermic.
I
F. SO2 is consumed.
F
Consider the reaction:
N2O4(g) Ù 2 NO2(g)
Write the equilibrium constant for this reaction in terms of the equilibrium constants, Ka
and Kb, for reactions a and b below:
a. N2(g) + 2 O2(g) Ù N2O4(g)
b. ½ N2(g) + O2(g) Ù NO2(g)
Question 5
4 Points
Whelan
NH4Cl(s) Ù NH3(g) + HCl(g)
.............
.............
Ka
Kb
K =
∆Ho = 268 kJ, and Kc = 5.10x10-6, at 548K:
A small amount of NH4Cl(s) is removed from the equilibrium system at constant T:
Circle the correct response for each:
3. The value of Q:
1. The value of Kc:
a. Is greater than K
a. Increase
b. Is equal to K
b. Decrease
c. Is less than K
c. Remain the same
2. The reaction will:
a. Produce more products
b. Produce more reactants.
c. Do nothing.
4. The concentration of NH3 will:
a. Increase
b. Decrease
c. Remain the same
Question 6
6 Points
Question 7
4 Points
Consider the following system at equilibrium at 698K.
2 HI(g) Ù H2(g) + I2(g)
Kc = 1.80x10-2
∆Ho = 10.4 kJ/mol
The production of I2(g) is favored by:
Circle those that apply
1. Removing H2(g)
5. Adding H2(g)
2. Decreasing the temperature
6. Increasing the temperature
3. Decreasing the volume
7. Increasing the volume
4. Adding a catalyst
8. Adding HI(g)
Give the formula for the:
a.
Conjugate base of HPO42--:
b.
Question 8
4 Points
Conjugate acid of HPO42-:
Which of the following can behave as
Bronsted-Lowry acids in aqueous solution?
Circle those that can
Question 9
6 Points
Question 10
5 Points
Question 11
4 Points
PO43H2PO4Which of the following can behave as
Bronsted-Lowry bases in aqueous solution?
Circle those that can
1. NH3
1. NH3
2. HNO2
2. HNO2
3. H2PO4-
3. H2PO4-
The hydroxide concentration in an aqueous solution is found to be 6.7x10-2M @ 25oC.
a. The hydronium ion concentration is:
1.49x10-13 M
b. The pH of this solution is:
12.83
c. The pOH of this solution is:
1.17
Classify each of the following substances:
1. Strong acid
a. Ca(OH)2
3
b. HNO2
2
2. Weak acid
c. MgCO3
5
3. Strong base
d. Sr(OH)2
3
4. Weak base
e. HNO3
1
5. Salt
Write a balanced Net Ionic equation for the reaction that occurs when aqueous solutions
of ammonium iodide and barium hydroxide are combined:
NH4+ + OH- = NH3(aq) + H2O(l)
The extent of this reaction is:
a.
>50%
b.
<50%
c.
100%
d.
Impossible to tell.
Question 12
4 Points
Question 13
6 Points
Question 14
6 Points
For the following reaction, K<1. Classify each of the reactants and products based on
their strength as Bronsted-Lowry acids or bases.
F- + CH3NH3+ Ù CH3NH2 + HF
a. F-
4
1. Stronger Bronsted-Lowry acid
b. CH3NH3+
2
2. Weaker Bronsted-Lowry acid
c. CH3NH2
3
3. Stronger Bronsted-Lowry base
d. HF
1
4. Weaker Bronsted-Lowry base
When the following solutions are combined the resulting pH of the solution will be –
greater that 7 (>7) – less than 7 (<7) – equal to 7 (=7)
a.
25mL of 0.3M nitric acid and 25mL of 0.3M ammonia:
<7
b.
35mL of 0.2M acetic acid and 35mL of 0.1M calcium hydroxide:
>7
c.
35mL of 0.3M hydroiodic acid and 35mL of 0.3M sodium hydroxide:
=7
Calculate the pH of a 0.33M hydrocyanic acid (HCN) solution.
Must show work and ICE table:
Approx:
I
C
E
A
HCN
0.33
-x
0.33-x
~ 0.33
+
H2O(l)
Ù
H3O+
0
x
x
x
+
CN0
x
x
x
Exact:
x = {0.33(4.0x10-10)}
½
x = 1.15x10-5 = [H3O+]
pH=
Question 15
6 Points
Calculate the pH of a 0.51M aniline (a weak base, C6H5NH2) solution.
Must show work and ICE table:
Approx:
I
C
E
A
C6H5NH2
0.51
-x
0.51-x
~ 0.51
+ H2O(l) Ù OH- +
0
x
x
x
C6H5NH3+
0
x
x
x
Exact:
x = {0.51(7.4x10-10)}
½
x = 1.94x10-5 = [OH-]
pH=
Question 16
7 Points
Calculate the pH of a 7.33x10-2M aqueous solution of ammonium perchlorate, NH4ClO4 ?
Must show work and ICE table:
Approx:
Exact:
I
C
E
A
NH4+
0.0733
-x
0.0733-x
~0.0733
+
H2O(l)
Ù
H3O+
0
x
x
x
+
NH3
0
x
x
x
x = {0.0733(5.56x10-10)}
½
x = 6.38x10-6 = [H3O+]
Kb = 1x10-14/1.8x10-5 = 5.56x10-10
pH=
Question 17
4 Points
Question 18
4 Points
Circle the atom on each of the following molecules that can act as an active Lewis base
site.
N2(g) + 3H2(g) Ù 2NH3(g)
T(oC)
25
200
300
K
6.4x102
4.4x10-1
4.3x10-3
From the data given on the left it can be inferred that:
(Circle those that are correct)
1. NH3 production is favored at high temperatures
2. NH3 production is favored at low temperatures
3. The reaction is endothermic
4. The reaction is exothermic
5. The reaction is fast
Question 19
3 Points
The pH of an aqueous solution of 0.59M hydroselenic acid, H2Se(aq), is:
I
C
E
A
H2Se
0.59
-x
0.59-x
~ 0.59
+
H2O(l)
Ù
H3O+
0
x
x
x
+
HSe0
x
x
x
x = {0.59(1.3x10-4)}
½
x = 8.76x10-3 = [H3O+]
pH=
Question 20
3 Points
The Se2- concentration of an aqueous solution of 0.59M hydroselenic acid, H2Se(aq), is:
HSe-
+
H2O(l)
Ù
H3O+
+
Se-2
100Ka2 < [HSe-] = 8.76x10-3
[Se2-] = Ka2
[Se2-]
Do Not Write Below This
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Exam II Score