1. No category

Name
Chemistry 1B
Exam 1 Version A
Section
Score
Fall 2014
/100
Questions 1, 2, and 3 relate to the following hypothetical equation at equilibrium
in a closed container:
aA(aq) + bB(s)
cC(g) + dD(aq)
∆H = – 200 kJ.
For each question below determine whether the reaction would shift to the Left, to
the Right, have No effect, or, Cannot tell from the information given.
"
1)
Some B is removed from the container.
Solid
(a) Right (b) Left (c) No effect (d) Cannot tell
2)
The container is heated.
Exothermic
(a) Right (b) Left (c) No effect (d) Cannot tell
3)
The size of the container is increased.
Gas
(a) Right (b) Left (c) No effect (d) Cannot tell
4)
Hydrazine, N2H4 is a weak base, Kb = 3.0 x 10–6. Find the pH of an aqueous
2.0 M solution of its conjugate acid, N2H5+.
(a)
5)
– 0.30
(b)
5.52
(c)
8.48
(d)
Find the pH of 100.0 mL of an aqueous 0.43 M Ba(OH)2 solution
(a)
0.37
(b)
12.63
(c)
12.93
(d)
4.09
(e)
Two OH—
13.63 (e)
6)
Under the Brønsted concept of acids and bases, a base is:
(a)
a proton donor.
(b)
a proton acceptor, (c)
a hydroxide donor
(d)
an electron pair donor
(e)
opposite of a nonelectrolyte.
7)
Which of the following is the strongest acid ?
8)
(a)
Ascorbic Acid,
(b)
Benzoic Acid,
(c)
3–chlorobenzoic acid,
(d)
2–hydroxybenzoic acid,
(e)
Chloroacetic acid,
Ka = 8.0 x 10–5
Ka = 6.5 x 10–5
Ka = 1.5 x 10–4
Ka = 1.1 x 10–3
Ka = 1.4 x 10–3
9.91
13.93
pKa = 4.10
pKa = 4.18
pKa = 3.82
pKa = 2.95
pKa = 2.84
If you want to make a buffer of pH = 4.00, which of the acids in (7) above with
its conjugate base would be best ?
(a)
(b)
(c)
(d)
(e)
Page 1
9)
Which of the following is not true about a chemical system at equilibrium ?
(a)
no reactions take place.
(b)
the rates of forward and reverse reactions are equal.
(c)
temperature changes can affect concentrations.
(d)
if the system is disturbed it will attempt to re-establish equilibrium.
(e)
the equilibrium constant relates reactant and product concentrations.
10)
Which of the following correctly relates the two equilibrium constants for the
two reactions shown ?
NOCl(g) ⇌ NO(g) + 12 Cl2(g)
K1
2 NO(g)
11)
Cl2(g)
⇌
2 NOCl(g)
1
(a)
K2 = – K1
(b)
K2 =
(d)
K2 = 2 K1
(e)
K2 = – 2 K1
K1
1.6 x 10–16
(e)
(c)
K2 =
1
K12
9.3 x 10–9
The following reaction is at equilibrium.
2 NO2(g) ⇌ N2O4(g)
K = 180.
If [N2O4] = 4.6 x 10–5 M, what is [NO2] ?
(a)
1980 M
(b)
4.6 x 10–5 M
(c)
(d)
13)
K2
Given the following two equilibria:
PbI2(s) ⇌ Pb2+(aq) + 2 I–(aq)
K1 = 8.7 x 10–9.
PbSO4(s)
⇌ Pb2+(aq) + SO42–(aq)
K2 = 1.8 x 10–8.
calculate the equilibrium constant for the following reaction:
PbSO4(s) + 2 I– ⇌ PbI2(s) + SO42–(aq)
K3 = ? = K2 ÷ K1
(a)
0.48
(b)
6.4 x 1015
(c)
2.1
(d)
12)
+
5.1 x 10–4 M
(e)
3.9 x 106 M
2.6 x 10–7 M
For the following reaction:
2 COF2(g) ⇌ CO2(g) + CF4(g) K = 2.00 at 1000°C.
If we have the concentrations of [COF2] = 0.255 M, and [CF4] = 0.118 M, and
[CO2] = 1.50 M, which of the following is correct:
Q = 3.50
(a)
The system is at equilibrium and no change will occur.
(b)
The system is at equilibrium and will shift to the left.
(c)
The system is at equilibrium and will shift to the right.
(d)
There is too much reactant and the system will shift right.
(e)
There is too much product and the system will shift left.
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14)
For the following reaction:
C(s) + H2O(g)
⇌ CO(g) + H2(g)
Change all to Molarity: ÷ 50.
Initially 2.5 moles of H2O and 8.1 moles of C are placed in a 50.0 L container.
After the system comes to equilibrium [H2] = 0.040 M. Which of the following is true ?
(a)
(d)
15)
[H2O] = 0.020 M
(b)
No Carbon remains
For the following reaction:
2 N2O(g) + N2H4(g) ⇌
(e)
[H2O] = 0.010 M
(c)
[CO] = 0.020 M
None of these.
3 N2(g) + 2 H2O(g)
If we start with 0.10 mol N2O and 0.25 mol N2H4 in a 10.0 L container, and at
equilibrium there are 0.06 mol of N2O,
How many moles of N2 are present at equilibrium ?
(a)
(d)
16)
0.09
0.02
(a)
(b)
(c)
(d)
(e)
0.06
H3O+(aq) + F–(aq)
HF is an acid and H3O+ is its conjugate base.
H2O is an acid and H3O+ is its conjugate base.
HF is an acid and F– is its conjugate base.
H2O is an acid and O2– is its conjugate base.
HF is an acid and H2O is its conjugate base.
HC2H3O2
(e)
Ba(OH)2
(c)
(CH3)NH2
Which of the following will have the lowest pH if all are 0.10 M ?
(a)
NH4Cl
(b)
KC2H3O2
(c)
KBr
(d)
19)
⇌
Which of the following is a weak base ?
(a)
KOH
(b)
NH4Cl
(d)
18)
0.04
(c)
None of these.
In the following reaction:
HF(aq) + H2O
17)
(b)
(e)
NaNO2
(e)
NaCl
Which of the following will be the strongest acid ( all are 0.10 M ) ?
(a)
(CCl3)CO2H
(b)
(CCl2H)CO2H
(c)
(CClH2)CO2H
(d)
(CH3)CO2H
(e)
not enough information
In lecture notes. This was an example of Induction.
Page 3
20)
A solution is made by mixing 50.0 mL of 0.40 M HClO ( Ka = 2.9 x 10–8 )
with 50.0 mL of 0.20 M KClO.
New volumes, NOT same molarity.
Find the pH of the resulting solution.
(a) 6.46
(b) 7.84
(c) 6.76
(d) 7.54
(e) 7.24
21)
The solution of a 0.10 M weak base has pH = 9.86. Find Kb for the base.
(a)
(d)
22)
1.38 x 10–10
1.91 x 10–7
(b)
(e)
5.24 x 10–8
1.91 x 10–9
(c)
7.24 x 10–5
Which of the following combinations will NOT produce a buffer solution ?
(a)
NaCl and HC2H3O2
(b)
NH4Cl and NH3
(c)
KCN and HCN
(d)
Na2HPO4 and NaH2PO4
(e)NaHCO3 and H2CO3
23)
A 1.00 L buffer solution is made using 0.500 moles of Benzoic acid, HC7H5O2
(Ka = 6.5 x 10–5), and 0.500 moles of sodium benzoate, NaC7H5O2 .
0.300 moles of HCl is added to the solution with no change in volume
(it remains 1.00 L total). Find the pH of the final solution.
Two parts: reaction and buffer.
(a) 3.59
(b) 3.98
(c) 4.19
(d) 4.41
(e) 4.79
24)
For the reaction:
2 HI(g)
H2(g) + I2(g)
The system is in equilibrium at 520°C when the partial pressures of the gasses are:
HI is 0.80 atm., H2 is 0.10 atm., and I2 is 0.10 atm.
So, K = 0.0156
⇌
Some HI is added to raise its partial pressure temporarily to 0.96 atm.
When equilibrium is restored, what will be the partial pressure of HI ?
(hint: this can be done without the quadratic formula.)
(a) 0.80 atm.
25)
(b) 0.84 atm.
(c) 0.88 atm.
(d) 0.93 atm.
(e) 0.96 atm.
For the reaction:
2 SO2(g) + O2(g)
⇌ 2 SO3(g)
K = 1.2
If 1.5 mol SO2, 4.0 mol O2, and 2.0 mol SO3 are introduced into a 1.00 L flask, what
changes in concentration (if any) will be observed as the system reaches equilibrium ?
(a)
(b)
(c)
(d)
(e)
[SO2] increases; [O2] increases; [SO3] decreases
[SO2] increases; [O2] decreases: [SO3] decreases
[SO2] decreases; [O2] decreases: [SO3] increases
[SO2] decreases; [O2] increases: [SO3] increases
all concentrations remain the same.
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