Unit 4: Equilibrium Test
_____________________
April 11, 2011
Name
K _____/27 I _____/ 40 A _____/ 2
Modified True/False
K _____/ 5 I _____/ 3
Indicate whether the sentence or statement is true or false. If false, change the identified word or phrase to
make the sentence or statement true.
____
1. A precipitate forms when the ion product for the precipitate exceeds the Ksp. _________________________
____
2. Ksp values are temperature dependent. _________________________
____
3. For the gaseous equilibrium shown, 2A + 3B <====> 4C + D + heat.
If some B is added to the system, the quantity of C will decrease 4×'s as much as the quantity of D decreases.
______________________________
____
4. The pH scale ranges from 0 to 14. ___________________________________
____
5. A concentrated weak acid cannot have a lower pH than a dilute strong acid. _________________________
____
6. Conjugate acid base partners differ by a single proton. _________________________
____
7. If the pH of an aquatic solution at 95oC is 4.5 the pOH must be 9.5.
___________________________________
____
8. The Kb expression for H2PO41- is Kb = [OH1-][H3PO4] / [H2PO41-]. _________________________
Multiple Choice
K _____/ 1 I _____/ 8
Identify the letter of the choice that best completes the statement or answers the question.
____
9. For the equilibrium system below, which of the following would result in an increase in the quantity of
PCl5(g)?
PCl3(g) + Cl2(g) <=====> PCl5(g) + 45 kJ
a. increasing temperature
d. removing some Cl2(g)
b. increasing the size of the container
e. injecting some He gas
c. decreasing temperature
____ 10. 1.6 mol of CH3OH(g) are injected into a 4.0 L container and the following equilibrium becomes established.
2H2(g) + CO(g) <=====> CH3OH(g) + 92 kJ
If at equilibrium 0.80 mol of CH3OH is still in the container the Ke must be which of the following?
a. 0.78
d. 0.16
b. 25
e. 6.25
c. 5.0
____ 11. 4.5 mol of HI(g) are injected into a 5.0 L container and the following equilibrium was established.
H2(g) + I2(g) <=====> 2HI(g) + 65 kJ
If at equilibrium there was 4.0 mol of HI(g) left the Ke for this equilibrium must be which of the following?
a. 8.0
d. 0.063
b. 16
e. 0.016
c. 64
____ 12. Consider this equilibrium
4HCl(g) + O2(g) <=====> 2H2O(g) + 2Cl2(g)
The equilibrium law expression for the balanced chemical equation would be
a. [HCl][O2] / [H2O][Cl2]
d. [HCl]4[O2] / [H2O]2[Cl2]2
b. [H2O]2[Cl2]2/ [HCl]4[O2]
e. [H2O][Cl2]/HCl][O2]
c. 2[H2O][Cl2]/ 4[HCl][O2]
____ 13. The pH of a solution of HClO4 was found to be 3.4. The concentration of this solution in mol/L is which of
the following?
a. 4.0 × 10-4
d. 2.5 × 10-11
b. 3.4
e. none of the above
c. 0.29
____ 14. When 45 mL of 0.65 mol/L acetic acid is added to 65 mL of 0.45 mol/L sodium hydroxide the resulting mixture is/has a(n)
a. neutral
d. pH < 7
b. basic
e. both c and d
c. acidic
____ 15. When water is heated to its boiling point the system has which of the following?
a. increased entropy and decreased enthalpy
b. decreased entropy and increased enthalpy
c. increased both entropy and enthalpy
d. decreased both entropy and enthalpy
e. none of the above
____ 16. Kw is which of the following?
a. the equilibrium constant for water which is always 1.0 × 10-14
b. Ka × Kb for conjugate acid - base partners @ 25oC
c. the log[H2O] @ 25oC
d. both a and c
e. none of the above
____ 17. A solution of nitrous acid has a pH of 2.45. The [H1+] in mol/L and pOH must be respectively
a. 3.5 × 10-3, 11.55
d. 2.8 × 10-12, 12
b. 3.6 × 10-3, 11.55
e. 3.8 × 10-3, 12.55
c. 2.8 × 10-12, 11.6
Completion
K _____/ 6
Complete each sentence or statement.
18. If solutions of barium chloride and sodium sulfate were mixed and a precipitate formed, the precipitate would
be _________________________.
19. CO(g) + 2H2(g) → CH3OH(l); during this reaction the entropy ____________________.
20. A system at equilibrium always has forward and reverse reactions which are
___________________________________.
21. Baking soda, NaHCO3, acts like a base because _____________________________________________.
22. When nitric acid is titrated to an end point by lithium hydroxide the salt formed is
_________________________.
23. Bronsted and Lowry's definition of acids is acids are substances which _________________________.
Matching
K _____/ 8 I _____/ 4
Look at the entropy and enthalpy changes below and match them to spontaneity choices below.
a.
S is positive, H is positive
b.
S is negative, H is positive
c.
S is positive, H is negative
d.
S is negative, H is negative
____ 24. spontaneity temperature dependent, spontaneous at high T
____ 25. spontaneous at all temperatures
____ 26. nonspontaneous, proceeds only with continuous input of energy
Here is a list of weak acids. Match to its conjugate base partner below. If no match exists indicate by writing
none.
a. H2O
d. HPO421b. HSO4
e. H2CO3
c. HC2H3O2
f. H2C6H6O6
____
____
____
____
____
27.
28.
29.
30.
31.
C2H3O21SO42HC6H6O61PO43HCO31Each of the numbers below represent [H1+] ions in solution. Match these to the correct [OH1-] in the same solution. All numbers are in mol/L.
a. 3.4 × 10-3
c. 9.8 × 10-8
-5
b. 2.4 × 10
d. 1.7 × 10-4
____
____
____
____
32.
33.
34.
35.
4.2 × 10-10
5.9 × 10-11
2.9 × 10-12
1.0 × 10-7
Short Answer
K _____/ 7 I _____/ 3 A _____/ 2
36. The chemical calcium hypochlorite is used to control the growth of bacteria and algae in swimming pools. Although it is referred to as chlorine, how can the quantities of this chemical be monitored using a pH scale.
(2A)
37. What 2 ingredients are used to prepare a buffer solution. (2K)
38. Write the equilibrium expression for potassium nitrite that shows how its anion acts like a base. Make sure to
identify the 2 pairs of conjugate acid - base partners. (3K)
39. Explain the difference between a weak concentrated acid and a strong dilute acid. (2K)
40. If the [H1+] of a solution at 25oC is 4.9 × 10-4 mol/L, calculate the [OH1-] in mol/L, the pH and the pOH. (3I)
Problem
I _____/ 22
41. If the concentration of CO32- is found to be 1.3 × 10-4 mol/L in a saturated solution of Ag2CO3, what is the Ksp of
Ag2CO3? (3I)
42. What mass of Cu2S would be found in 34 L of a saturated solution of Cu2S if the Ksp of Cu2S is 1.6 × 10-48?
(3I)
43. What is the concentration of a monoprotic weak acid if its pH is 5.50 and its Ka = 5.7 × 10-10? (3I)
44. A weak base with a concentration of 1.3 mol/L has a percent ionization of 0.72%. What is the Kb of this weak
base? (3I)
45. What is the percent ionization of a 0.48 mol/L weak acid if its Ka = 1.4 × 10-9? (3I)
46. What is the pH of a 1.24 mol/L solution of HCN(aq) if its Ka = 6.2 × 10-10? (3I)
47. 28 mL of standardized 0.43 mol/L NaOH is titrated with 23 mL of 0.36 mol/L acetic acid. Calculate the pH of
the solution. (4I)
Unit 4: Equilibrium Test
Answer Section
MODIFIED TRUE/FALSE
1. ANS:
LOC:
2. ANS:
LOC:
3. ANS:
LOC:
4. ANS:
LOC:
5. ANS:
LOC:
6. ANS:
LOC:
7. ANS:
LOC:
8. ANS:
LOC:
T
CS2.05
T
CS2.01
F, will increase 4×'s as much
CS1.03
F, from below 0 and above 14
CS2.01
F, can have
CS1.02
T
CS2.06
F, pH + pOH = 14 only at 25oC
CS2.06
T
CS2.08
REF: I
OBJ: 7.6
REF: K/U
OBJ: 7.6
REF: I
OBJ: 7.3
REF: K/U
OBJ: 8.1
REF: K/U
OBJ: 8.1
REF: K/U
OBJ: 8.1
REF: I
OBJ: 8.1
REF: K/U
OBJ: 8.3
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
LOC:
LOC:
LOC:
LOC:
LOC:
LOC:
LOC:
LOC:
LOC:
MULTIPLE CHOICE
9.
10.
11.
12.
13.
14.
15.
16.
17.
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
C
E
C
B
A
B
C
B
A
REF:
REF:
REF:
REF:
REF:
REF:
REF:
REF:
REF:
I
I
I
I
I
I
I
K/U
I
7.3
7.5
7.5
7.2
8.1
8.4
7.7
8.1
8.2
CS1.03
CS2.06
CS2.06
CS1.02
CS2.06
CS2.08
CS1.05
CS1.07
CS2.06
COMPLETION
18. ANS:
LOC:
19. ANS:
LOC:
20. ANS:
LOC:
21. ANS:
barium sulfate
REF: K/U
CS1.06
decreases
REF: K/U
CS1.05
occurring at the same rate
REF: K/U
CS1.02
HCO31- steals a proton from water forming OH1- ions
REF: K/U
OBJ: 8.3
22. ANS: lithium nitrate
LOC: CS2.07
REF: K/U
OBJ: 7.6
OBJ: 7.7
OBJ: 7.1
OBJ: 8.4
LOC: CS2.08
23. ANS: donate protons
LOC: CS1.08
REF: K/U
OBJ: 8.1
MATCHING
24. ANS: A
25. ANS: C
26. ANS: B
REF: K/U
REF: K/U
REF: K/U
OBJ: 7.7
OBJ: 7.7
OBJ: 7.7
LOC: CS1.05
LOC: CS1.05
LOC: CS1.05
27.
28.
29.
30.
31.
ANS:
ANS:
ANS:
ANS:
ANS:
C
B
F
D
E
REF:
REF:
REF:
REF:
REF:
K/U
K/U
K/U
K/U
K/U
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
8.1
8.1
8.1
8.1
8.1
LOC:
LOC:
LOC:
LOC:
LOC:
CS2.01
CS2.01
CS2.01
CS2.01
CS2.01
32.
33.
34.
35.
ANS:
ANS:
ANS:
ANS:
B
D
A
C
REF:
REF:
REF:
REF:
I
I
I
I
OBJ:
OBJ:
OBJ:
OBJ:
8.2
8.2
8.2
8.2
LOC:
LOC:
LOC:
LOC:
CS2.06
CS2.06
CS2.06
CS2.06
SHORT ANSWER
36. ANS:
Hypochlorite ion, ClO1-,acts like a base in water forming OH1- ion when it steals a H atom from water. By
monitoring the pH of the pool water the [ClO1-]can be indirectly measured.
REF: MC
OBJ: 8.3
LOC: CS3.01
37. ANS:
A weak acid and a salt that contains its conjugate base partner OR
A weak base and a salt that contains its conjugate acid partner
REF: K/U
38. ANS:
NO31- + H2O(aq)
base-1 acid-2
OBJ: 8.5
<=====>
LOC: CS1.09
HNO3(aq) + OH1-(aq)
acid-1
base-2
REF: K/U
OBJ: 8.1
LOC: CS1.08
39. ANS:
- A concentrated acid has lots of solute particles in a given volume. A dilute acid has a small number of
solute particles in a given volume. A strong acid is completely ionized. A weak acid is only partially ionized.
- A weak concentrated acid has a high concentration of undissociated particles. A strong dilute acid has only
a small number of dissociated particles and no undissociated particles.
REF: K/U
OBJ: 8.2
LOC: CS1.08
40. ANS:
[OH1-] = 2.0 × 10-11 mol/L, pH = 3.31, pOH = 10.69
REF:
I
OBJ: 8.2
LOC: CS2.06
PROBLEM
41. ANS:
Ag2CO3(s) <====>
@E
+
2Ag1+(aq)
2 * 1.3 × 10-4
CO32-(aq)
1.3 × 10-4
Ksp = ( 2 * 1.3 × 10-4 )2 × 1.3 × 10-4
Ksp = 8.8 × 10-12
REF: I
42. ANS:
Cu2S(s) <====>
@E
OBJ: 7.6
LOC: CS2.03
2 Cu1+(aq)
2×
+
S2-(aq)
×
1.6 × 10-48 = 4×3
× = 7.4 × 10-17 mol/L
mCu2S = (7.4 × 10-17 mol/L)(34 L)(159.16 g/mol = 4.0 × 10-13 g
REF: I
OBJ: 7.6
43. ANS:
HX(aq) <=====> H1+(aq) + X1-(aq)
x
10-pH
10-pH
LOC: CS2.04
[H1+] = 10-pH = 10-5.50
[H1+] = 3.16 × 10-6 mol/L
(3.16 × 10-6)2 / × = 5.7 × 10-10
x = 1.8 × 10-2 mol/L
REF: I
44. ANS:
initial
shift
@E
OBJ: 8.2
XOH <=======>
1.3
LOC: CS2.06
X1+
+
1.3
OH1
(0.72)(1.3)/100
Ka = ((0.72)(1.3)/100)2 / 1.3 = 6.7 × 10-5
REF: I
45. ANS:
initial
shift
@E
OBJ: 8.2
LOC: CS2.06
HY(aq) <====> H1+(aq) + Y1-(aq)
0.48
-x
x
x
x
x
0.48 − x
x2 / 0.48 = 1.4 × 10-9
x = (1.4 × 10-9 × 0.48)0.5
pH = – log x
pH = 4.59,
% Ionization = 100(x / 0.48) = 5.4 × 10-3 %
REF: I
46. ANS:
OBJ: 8.2
LOC: CS2.06
HCN(aq) <====> H1+(aq) + CN1-(aq)
1.24
-x
x
x
x
x
1.24 − x
initial
shift
@E
x2 / 1.24 = 6.2 × 10-10
x = (6.2 × 10-10 × 1.24)0.5
pH = – log x
pH = 4.56
REF: I
47. ANS:
n=CV
(mol)
initial
reacted
left over
OBJ: 8.2
NaOH
+
(0.43 mol/L × 0.028 L)
0.01204
0.00828
0.00376
LOC: CS2.06
HC2H3O2 ----->
(0.36 mol/L × 0.023 L)
0.00828
0.00828
0
COH1- = n/V = 0.00376 mol / 0.051 L = 0.0737 mol/L
pOH = –log[0.0737] = 1.132
pH = 14 – 1.132 = 12.87
REF:
I
OBJ: 8.4
LOC: CS2.08
NaC2H3O2 + H2O