Dr. Bolaños
Spring 2016
CHEM 111- Exam #2A
NAME_______________________________________________________
There are 17 questions totaling 100 points. PLEASE look over the entire examination (6 pages total) BEFORE you begin to
ensure your packet is complete. REMEMBER: The best place to start your exam may not be at the beginning! You have 2
hours to complete this examination and may only use a basic scientific calculator, the resource sheet and the periodic table
provided. When specified, all work must be shown for credit AND all answers must be expressed with the proper amount of
significant figures. Please sign the honor code at the end of the document, when complete. A scratch sheet will be
provided by the instructor; please staple when you submit your exam. If you need further clarification, please speak with
the instructor. *** I certify that the work presented in this examination is my own and that the rules set-forth for this
examination were followed.
Signature: ___________________________________________________
Please answer all of the following questions. No work is required for Questions 1-9 (no partial
credit!). Show ALL work for credit for Questions 18-21.
1. The equilibrium, constant for a reaction is 4.34 x 10-3 at 300 oC. At equilibrium, which predominates? (1.5 pts)
a. Products are only present
b. Reactants are only present
c. Products predominate
d. Reactants predominate
e. Both are present roughly at the same amount
2. For weak acids, as the percent ionization decreases, the hydroxide ion concentration __________________.
(1.5 pts)
3. The conjugate acid of HCO3- is __________________________. An example of an Arrhenius base is
__________________. The PO43- can _____________________ this number ______ of protons (H+). (4 pts
total, 1 pt each))
4. For the set below, the weakest acid is______________ and the strongest acid is _________________. (4 pt
total, 2 pts each))
HBrO
HIO2
HClO2
HIO
5. True
or False ? (circle one) For an endothermic reaction at equilibrium, if more reactants are added,
the K value increases. (1.5 pts)
6. True
or
False ? (circle one) HF is a strong acid. (1.5 pts)
7. The pH of a 1.30 x 10-1 M HNO3 solution is __________________. Watch S.F.! (2.5 pts)
8. The pOH of a KOH solution is 4.67. The [H3O]+ is __________________________. Watch S.F.! (4 pts)
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Dr. Bolaños
Spring 2016
CHEM 111- Exam #2A
9. At 400K, Kp = 7.0 for the reaction below. (1.5 pts)
2 BrCl (g)
Kp = 7.0
Br2 (g) + Cl2 (g)
A closed vessel at 400 K has partial pressures of 1 atm Cl2, 1 atm Br2 and 2 atm BrCl. The scientist wonders if the
system is at equilibrium. Please determine which of the statements below is true.
a. The equilibrium partial pressures of Cl2, Br2 and BrCl will be the same as the initial values.
b. The reaction will go to completion since there are equal amounts of Cl2 and Br2 .
c. The equilibrium partial pressure of Br2 will be greater than 1 atm.
d. The equilibrium partial pressure of BrCl will be greater than 2 atm.
e. At equilibrium, the total pressure in the vessel will be less than the initial total pressure.
10. What is the Kc expression for the reaction below? (2.5 pts)
4 CuO (s) + CH4
(g)
CO2 (g) + 4 Cu (s) + 2 H2O (g)
11. Consider the data in the table below and assume that all solutions are 1.0 M. The weakest conjugate base
is ________________________ and the strongest acid is ___________________________________. (4 pts
total, 2 pts each)
Ka
HNO2 (aq)
HCHO2 (aq)
-4
-4
4.6 x 10
1.8 x 10
HClO (aq)
2.9 x 10
-8
HCN (aq)
4.9 x 10-10
12. Consider each substance dissolved individually in beakers to 0.100 M solutions. (5 pts total)
a. LiClO3
b. H2NNH3+
c. NaClO2
d. KNO2
e. KCl
a. List the letter(s) for the neutral solutions_________________________
b. List the letter(s) for the basic solutions___________________________
c. The strongest base is ____________________________
13. At a given temperature, the Kp for the Born-Haber reaction below will be _________________________ Kc.
Fill-in Choices: equal to, greater than, less than. (2.5 pts)
N2 (g) + 3H2 (g)
2 NH3 (g)
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Dr. Bolaños
Spring 2016
CHEM 111- Exam #2A
14. Consider the exothermic reaction below and provide the correct responses. (8 pts total, 1 point each)
2 SO3 (g)
2 SO2 (g) + O2 (g)
“Stress” on RXN
Effect(s) on Equilibrium
(Directional Shift, if any)
Kc Change
(increase, decrease, no change)
Adding SO3
Decreasing the
volume of
container
Increasing the
RXN
Temperature
Adding a
catalyst
15. Consider the two reactions below at 25 oC. The value of Kc for the RXN 2 is ____________________. (5 pts)
Show work for credit.
RXN 1:
RXN 2:
H2 (g) + I2 (g)
1 HI (g)
2
Kc = 812
2 HI (g)
1 H (g) +
2
4
3
1 I (g)
2
4
Kc = ?
Dr. Bolaños
CHEM 111- Exam #2A
Spring 2016
16. At 25 oC, a reaction vessel with a volume of 500.0 mL initially contains 4.59 g of NO gas and 6.57 g of oxygen
gas. What the concentration, in molarity for the NO2 gas at equilibrium? Show all work for credit. (8 pts)
2 NO (g) + O2 (g)
2 NO2 (g)
Kp = 2.91 x 10-4
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Dr. Bolaños
CHEM 111- Exam #2A
Spring 2016
17. Consider an aqueous solution of 0.100 M HI . If the Ka is 3.2 x 109, what is the percent dissociation? Show
ALL WORK FOR CREDIT. (8 pts)
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Dr. Bolaños
CHEM 111- Exam #2A
18. What is the pH of a 0.850 M pyruvic acid (Ka = 4.10 x 10-3) solution? (8 pts)
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Spring 2016
Dr. Bolaños
CHEM 111- Exam #2A
Spring 2016
19. An aqueous solution contains 0.291 M sodium cyanide (NaCN) and has a pH of 11.56. Show all work for
credit. (10 pts)
a. What is the Kb of monobase? (8pts)
b. What is the Ka of the conjugate acid? (2 pts)
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Dr. Bolaños
CHEM 111- Exam #2A
Spring 2016
20. What is the concentration of a mixture containing 0.050 M HI and 3.50 M formic acid, HCHO2. Show all
work for credit. (8 pts)
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Dr. Bolaños
CHEM 111- Exam #2A
Spring 2016
21. At my first internship at BASF Chemical company in Freeport, Texas, I worked in the waste division. One of
our jobs was to find a marketable use for the waste products used to produce plastics. Adipic acid,
H2C6H8O4, was one of these products. On the second day of work, a drop of adipic acid fell on my new
leather dress shoes and burned a hole through some of the leather (and they were $100 then, very
expensive!). I am sure I would have been fired if I was wearing sandals and had an acid accident on the
second day! What is the pH and concentration of ALL species at equilibrium, if the initial concentration of
adipic acid is 0.100 M? Please “BOX” your labeled answers. Show ALL work for credit! (12 pts)
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Dr. Bolaños
Spring 2016
CHEM 111- Exam #2A
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Dr. Bolaños
CHEM 111- Exam #2A
Resources:
Kp = Kc(RT)∆n
Ka*Kb = Kw
[H3O+]= 10-pH
R = 0.08206 L * atm /mol*K
Kw = 1.0 x 10-14 = [H3O+][OH-]
pH = -log[H3O+]
pH + pOH = 14
Acid Dissociation Constants at 25 oC
Name
Formula
Ka Value(s)
Formic
HCHO2
1.8 x 10-4
Hydrocyanic
HCN
4.9 x 10-10
Chlorous acid
HClO2
2.9 x 10-8
Adipic Acid
H2C6H8O4
3.9 x 10-5 (Ka1); 3.9 x 10-6 (Ka2)
Nitrous Acid
HNO2
4.6 x 10-4
Pyruvic acid
HC3H3O3
4.1 x 10-3
Base Association Constants at 25 oC
Name
Ammonia
Formula
NH3
Kb Value(s)
1.76 x 10-5
hydrazine
H2NNH2
1.3 x 10-6
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Spring 2016