Chemistry 116: Exam 4 (AM)
April 11, 2017
1. What is the solubility of AgI (234.77 g/mole) in grams per liter at a temperature when its KSP is
1.45×10−16?
a. 1.20×10−8 g/L
b. 7.77×10−4 g/L
c. 3.31×10−6 g/L
d. 2.83×10−6 g/L
2. Calculate the pH change when 0.15 mole of OH− is added to 1.00 liter of a buffer containing 1.14
M sodium dihydrogen phosphate and 1.14 M sodium hydrogen phosphate.
a. A change of 0.057 pH units
b. A change of 0.82 pH units
c. A change of 0.23 pH units
d. A change of 0.15 pH units
e. A change of 0.11 pH units
3. Calculate ∆S° for the reaction N2(g) +2O2(g) → 2NO2(g)
a.
b.
c.
d.
−156.5 J/K
−121.7 J/K
+15.5 J/K
+636.5 J/K
N2(g)
O2(g)
NO2(g)
S0 in J/K
191.5
205.0
239.9
4. The following plot shows a titration curve for the titration of 1.00 L of 1.00 M diprotic acid H2A
with NaOH. A buffer region is indicated by which point(s) a-d?
a. point a
b. points a and c
c. point b
d. points b and d
5. What is the pH of a solution resulting from the addition of 30.0 mL of 0.050 M HNO3 to 25.0 mL
of 0.10 M KOH?
a. 1.56
b. 1.34
c. 1.74
d. 11.96
e. 12.26
It’s not that I’m so smart, it’s just that I stay with problems longer.” ~ Albert Einstein
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Chemistry 116: Exam 4 (AM)
April 11, 2017
6. A titration of 25.0 mL of formic acid (HCOOH, KA=1.77×10−4) requires 36.0 mL of 0.100 M
NaOH to reach equivalence. What is the pH at this point?
a. 2.49
b. 5.73
c. 11.51
d. 8.26
7. In which aqueous system is Hg2Cl2 least soluble?
a. 0.3 M KCl
b. 0.2 M CaCl2
c. H2O
d. 0.2 M HCl
e. 0.5 M HNO3
8. The following plot shows two titration curves, each representing the titration of 50.00 mL of 0.100
M acid with 0.100 M NaOH. At which point is the pKA of the acid equal to the pH?
9. A saturated solution of barium sulfate (BaSO4) contains 1.08×10−5 M Ba2+(aq). What is the KSP of
barium sulfate?
a. 5.03×10−15
b. 2.16×10−5
c. 3.67×10−19
d. 1.16×10−10
10. Calculate the solubility of silver chromate, Ag2CrO4, in 0.0050 M Na2CrO4. Ksp = 2.6×10–12
a. 1.4×10–4 M
b. 3.4×10–5 M
c. 1.1×10–5 M
d. 1.6×10–6 M
It’s not that I’m so smart, it’s just that I stay with problems longer.” ~ Albert Einstein
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Chemistry 116: Exam 4 (AM)
April 11, 2017
11. The following pictures represent solutions that contain a weak acid HA and its potassium salt KA.
(K+, H3O+ initially present, OH− initially present and solvent water molecules have been omitted
for clarity.)
Which picture represents the equilibrium state of the solution after addition of one OH− ion to the
solution shown in picture (1)?
12. Which of the following processes have a positive value of ∆S
a. NaCl(s) → NaCl(aq)
b. H2O(l) → H2O(s)
c. 2H2S(g) + 3 O2(g) → 2H2O(l) + 2 SO2(g)
d. a, b, and c all have ∆S > 0
e. only a and b have ∆S>0
13. When 50 mL of 0.10 M NaF is added to 50 mL of 0.10 M HF, relative to the pH of the 0.10 M HF
solution the pH of the resulting solution will
a. become 7
b. decrease.
c. increase
d. remain the same
14. What is the Ksp for Ag3PO4 if its molar solubility is 1.76×10−5 mole/L?
a. 3.10×10−10
b. 2.18×10−14
c. 8.64×10−19
d. 7.04×10−5
e. 2.59×10−18
15. The 1996 Nobel prize in physics was awarded to Douglas Osheroff, Robert Richardson, and david
lee for discovering superfluidity (apparently frictionless flow) in 3He. When 3He is cooled to
0.0027K, the liquid settles into an ordered superfluid state. What is the predicted sign of the
entropy changing for the conversion of liquid 3He into its superfluid state?
a.
b.
c.
d.
Zero since both states are liquids
Indeterminant
Negative due to the conversion into a more ordered state
Positive due to the conversion into a more ordered state
It’s not that I’m so smart, it’s just that I stay with problems longer.” ~ Albert Einstein
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Chemistry 116: Exam 4 (AM)
April 11, 2017
For questions 16 through 18 consider solid sodium fluoride (NaF) slowly added to a water sample that
contains 0.0410 M Ba2+ ion and 0.0505 M Ca2+ ion.
KSP of BaF2 is 1.00×10−6. KSP of CaF2 is 3.90×10−11.
16. What metal cation will precipitate first?
a. Na+
b. Ca2+
c. Ba2+
17. What is the concentration of fluoride ion when the second metal cation begins to precipitate?
a. 1.98×10−5 M
b. 2.44×10−5 M
c. 3.08×10−5 M
d. 4.94×10−3 M
e. 1.00×10−3 M
18. What is the concentration of the first metal cation to precipitate when the second metal cation
begins to precipitate
a. 7.89×10−9 M
b. 3.08×10−5 M
c. 1.60×10−6 M
d. 0.0410 M
e. 1.97×10−6 M
19. The following pictures represent solutions at various points in the titration of a weak acid HA with
aqueous KOH. Unshaded spheres represent H atoms, black spheres represent oxygen atoms, and
shaded spheres represent A− ions. Which picture represents the solution before the equivalence
point but after the start of the titration? Note: K+, H3O+ initially present, OH− initially present and
solvent water molecules have been omitted for clarity.
a.
b.
c.
d.
It’s not that I’m so smart, it’s just that I stay with problems longer.” ~ Albert Einstein
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Chemistry 116: Exam 4 (AM)
April 11, 2017
20. A 25. mL sample of a weak acid solution (KA= 4.3×10−4) is titrated with 0.20 M NaOH. If 20.68
mL of NaOH are needed to reach the equivalence point, what is the pH halfway to the equivalence
point?
a. 3.37
b. 5.85
c. 9.26
d. 4.74
21. Which compound below has the strongest base strength?
a. Pyridine, pKB= 8.79
b. Aniline, pKB= 9.4
c. Ammonia, pKB=4.75
d. Acetate ion, pKB= 9.3
e. Methylamine, pKB= 3.36
Key (versions B, D, and E)
4. B
1. D
5. E
2. E
3. B
6. D
7. B
8. A
9. D
10. C
11. B
12. A
13. C
14. E
15. C
16. B
17. D
18. C
19. B
20. A
21. E
Key (versions A, C, and F)
1. A
4. B
2. D
5. A
3. C
6. C
7. E
8. C
9. B
10. A
11. E
12. B
13. D
14. C
15. D
16. E
17. B
18. B
19. E
20. D
21. B
It’s not that I’m so smart, it’s just that I stay with problems longer.” ~ Albert Einstein
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