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Multiple Choice
Stoichiometry/Chemical Reactions
1. (2 points) Carbon monoxide and oxygen gas are combined in a reaction vessel and react completely to
form carbon dioxide. Which mixture of gases will react to create the highest yield of CO2 ?
A. 1.0 L CO and 4.0 L O2
B. 2.0 L CO and 3.0 L O2
C. 3.0 L CO and 2.0 L O2
D. 4.0 L CO and 1.0 L O2
2. (2 points) The metabolism of sucrose, C12 H22 O11 , can be thought of as a form of combustion. If I were to
consume a whole pack of m&ms (31.0 g of sucrose), how much oxygen would I need to stoichiometrically
digest it all?
A. 17.4 g

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B. 34.8 g
C. 69.6 g
D. 139 g

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3. (2 points) 3.0 g of an unknown hydrocarbon was burned in excess oxygen. If 6.0 g of water is formed
as a product, what is the mass percentage of hydrogen in the mystery compound?
A. 22 %
B. 39 %
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C. 44 %
D. 77 %
4. (2 points) Zinc metal is added to an acidic solution and reacts according to the following equation: Zn
A

(s) + 2 H+ (aq) −−→ Zn2+ (aq) + H2 (g). What is the maximum volume of hydrogen gas that can be
produced from 10.0 g of zinc at STP?
A. 0.857 L
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B. 1.51 L
C. 3.43 L
D. 6.85 L
5. (2 points) A 20.00 g sample of a sodium salt with an unknown sulfur oxide anion contains 8.11 g of
sulfur and 6.07 g of oxygen. What is the identity of the anion?
A. SO4 2 –
B. SO3 2 –
C. S2 O3 –
D. S2 O3 2 –
6. (2 points) What is the concentration of an aqueous 3.0% w/w H2 O2 solution? You may assume the
density of the solution is the same as pure water.
A. 0.74 M
B. 0.86 M
C. 0.88 M

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 D. 0.91 M
7. (2 points) What is the w/w ratio of ethanol (C2 H5 OH) to water in a 3 molal solution of ethanol?
A. 0.121
B. 0.138
C. 0.333
D. 0.400
8. (2 points) 10.0 g of phosphorus and 24.0 g of chlorine gas react according to the following equation:
P4 (s) + 6 Cl2 (g) −−→ 4 PCl3 (l). If 26.3 g of PCl3 are formed, what is the percent yield of this reaction?
A. 14.8 %
B. 28.3 %
C. 59.3 %
D. 84.9 %
9. (3 points) Timmy has a splitting headache, but because he is frugal, he decides to make his own aspirin

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(acetylsalicylic acid) instead of buying some at the pharmacy. The reaction that he is carrying out is:

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If he has 45.0 g of salicylic acid (C7 H6 O3 ) and 23.0 g of acetic anhydride (C4 H6 O3 ), what is the minimum
amount of aspirin (C9 H8 O4 ) he needs to make to have an 80.0 % yield?
A

A. 32.5 g
B. 40.6 g
C. 50.7 g
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D. 59.3 g

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 Equilibrium
10. (2 points) A sample of nitrogen dioxide dimerizes reversibly in a rigid container. Select all of the
following changes that would shift the reaction towards the right. 2 NO2 −
↽−
−⇀
− N2 O4 ∆H = -57 kJ/mol
A. Increasing the volume of the reaction vessel
B. Increasing the pressure by adding nitrogen
C. Increasing the pressure by adding more N2 O4
D. Increasing the pressure by adding more NO2
E. Cooling the reaction vessel
11. (2 points) PCl5 decomposes reversibly in a vessel with a movable piston and constant external pressure.
Select all of the following changes that would shift the reaction towards the right. PCl5 −
↽−
−⇀
− PCl3 + Cl2
∆H = +88 kJ/mol.
A. Increasing the volume of the reaction vessel
B. Adding helium to the reaction vessel

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C. Adding chlorine to the reaction vessel
D. Adding a catalyst

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E. Heating the reaction vessel
12. (2 points) Ammonia is produced from elemental nitrogen and hydrogen gases in a rigid container. Select
all of the following that would shift the reaction towards the left. N2 + 3 H2 −
↽−
−⇀
− NH3 ∆H = -22 kJ/mol
A. Decreasing the volume of the reaction vessel
B. Increasing the pressure by adding hydrogen
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C. Adding a catalyst
D. Heating the reaction vessel
E. Increasing the volume of the reaction vessel
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13. (2 points) A sample of sulfur dioxide is oxidized to sulfur trioxide in the presence of oxygen. This
reaction takes place with in a vessel that maintains a constant total pressure of 10.0 bar. For the
following reaction, select all of the following that would shift the reaction towards the left. 2 SO2 (g) +
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−−
O2 (g) ↽−⇀
− 2 SO3 (g) ∆H = -197 kJ/mol
A. Decreasing the volume of the reaction vessel
B. Adding argon to the reaction vessel
C. Adding a catalyst
D. Cooling the reaction vessel
E. Adding oxygen to the reaction vessel
14. (2 points) What is the pH of a 0.3 M solution of CH3 COOH? The pK a of CH3 COOH is 4.76.
A. 0.52
B. 2.64
C. 3.14
D. 4.12
15. (2 points) What is the pH of a 0.5 M solution of NH3 ? The pK b of NH3 is 4.75.
A. 2.53
B. 9.78

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 C. 10.22
D. 11.47
16. (2 points) What is the pH of a 3.8 M solution of NH4 CH3 COO? Use the pK a /pK b values provided in
previous questions.
A. 4.76
B. 5.8
C. 7
D. 9.25
17. (3 points) What is the pH of a 8 · 10−8 M solution of HCl?
A. 5.9
B. 6.83
C. 6.99
D. 9

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18. (4 points) A student is trying to experimentally determine the molar mass of an acid. The student
knows that the pK a is 3.8, and after adding 250 mL of 1.0 M NaOH to a solution with 50 g of the acid
dissolved in 1 L of water, it has a pH of 4.2. What is the approximate molar mass of the acid?
A. 28 g/mol
B. 56 g/mol
C. 98 g/mol
D. 143 g/mol
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19. (3 points) What volume of a 2.0 M solution of NaOH is necessary to add to a 250 mL solution with 14
g of NH4 Cl dissolved in it in order to maximize buffering capacity?
A. 65.4 mL
B. 131 mL
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C. 262 mL
D. It is already at maximum buffering capacity
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20. (3 points) What is the pH of the buffer in the previous question? The pK b of NH3 is 4.75.
A. 4.75
B. 5.32
C. 7
D. 9.25

21. (4 points) How much anhydrous ammonia is required to dissolve 20 g of AgCl in 500 mL of water?
Ksp [AgCl] = 1.8 · 10−10 , Kf [Ag(N H3 )+
2 ] = 1.7 · 10
7

A. 4.8 g
B. 43 g
C. 48 g
D. 109 g

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 Free Response
Stoichiometry/Reactions
22. (14 points) Predict the reaction products for the following reactions. Completing the net ionic equation
is sufficient. It is also possible that no reaction happens. It is not necessary to balance equations.

(a) (1 point) Na2 SO4 + BaCl2 −−→

(b) (1 point) H2 S + CdCl2 −−→

(c) (1 point) NaOH + HCl −−→

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(d) (2 points) HCl + Al(s) −−→

(e) (2 points) HCl + Cu(s) −−→

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∆
(f) (2 points) CaCO3 (s) −−→
A

(g) (2 points) CrO3 (s)+ H2 O −−→

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(h) (3 points) KMnO4 + NaOH + H2 O2 −−→

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23. (10 points) Phoenix got in trouble for mysterious stimulants and has turned to more mild alternatives.
He has a powder that contains only carbon, hydrogen, nitrogen and oxygen. Burning a 5.00 g sample of
this compound in excess oxygen yields 9.065 g CO2 , 2.319 g H2 O, 4.739 g NO2 .
(a) (4 points) Calculate the mole ratios of the different elements.

(b) (2 points) Determine the empirical formula of this compound.

(c) (4 points) Given that the molar mass of the compound is between 150 and 250 g/mol, what is the
molecular formula for this compound?

(d) (0.1 points) Bonus: Can you identify this compound?

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 Equilibrium
24. (19 points) Balance the following chemical reactions using the lowest whole number coefficients.

(a) (1 points) HgO(s) −−→ O2 (g) + Hg(l)

(b) (1 points) N2 (g) + H2 (g) −−→ NH3 (l)
(c) (1 points) C6 H12 O6 (s) + O2 (g) −−→ CO2 (g) + H2 O(g)
(d) (1 points) Na(s) + H2 O(l) −−→ NaOH(aq) + H2 (g)
(e) (1 points) P4 (s) + O2 (g) −−→ P2 O5 (s)
(f) (1 points) H2 O2 (aq) −−→ H2 O(l) + O2 (g)

Give the balanced chemical equation for the following redox reactions in acidic conditions (You may
need to add H2 O(l) and/or H+ (aq) to either side of the equation):

(g) (2 points) MnO4 – (aq) + Fe2+ (aq) −−→ Mn2+ (aq) + Fe3+ (aq)

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(h) (3 points) NO3 – (aq) + I – (aq) −−→ NO(g) + I2 (s)
(i) (3 points) ClO3 – (aq) + Cl – (aq) −−→ Cl2 (g) + ClO2 (g)

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Give the balanced chemical equation for the following redox reactions in basic conditions (You may
need to add H2 O(l) and/or OH – (aq) to either side of the equation):

(j) (3 points) Al(s) + NO2 – (aq) −−→ AlO2 – (aq) + NH3 (aq)
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(k) (2 points) MnO4 – (aq) + NO2 – (aq) −−→ MnO2 (s) + NO3 – (aq)
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25. (35 points) Colloquially, we typically use the word “salt” to describe a very specific compound: sodium
chloride, our common table salt! However, chemists use the word “salt” to describe any ionic compounds.
The specifics of salt dissolution are of particular interest to chemists studying equilibrium.
(a) (6 points) When salts dissolve in water, they can create acidic, basic, or neutral solutions. On you
answer sheet, organize the following salts based on the pH of the solution when dissolved in water.
- NH4 I
- NaCl
- KOH
- Cs3 PO4
- KHCO3
- FeCl3
(b) (3 points) Explain your reasoning used in part a (three sentences or less).

The solubility of salts depends on a variety of factors, including the properties of the cations and
anions involved. Many silver salts are insoluble, but the degree of their solubilities depends on the
identity of the anion.

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(c) (2 points) Order the solubilities of the silver halides (AgX, where X = F, Cl, Br, I) in terms of
increasing solubility in water.

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(d) (4 points) Justify your answer in part c in terms of Hard and Soft Acid Base Theory.

(e) (2 points) The solubility of salts may also depend on the pH of the solution. Shown below is the
reaction for the dissolution of CaF2 .
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−− 2+ –
CaF2 (s) ↽−⇀
− Ca (aq) + 2 F (aq)

Write out the equation for the solubility product, Ksp , for the dissolution of CaF2 .
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(f) (2 points) Do you expect CaF2 to be more soluble in a solution with a high pH or low pH?
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(g) (3 points) Justify your answer to part f. Include another equilibrium equation in your explanation.

(h) (3 points) Calculate the molar solubility of CaF2 in a neutral solution of water. The Ksp of CaF2
is 3.9 ×10−11 at 25°C.

(i) (10 points) Calculate the molar solubility of CaF2 in a solution at pH = 3.00. The pK a of HF is
3.17.

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