name __________
CHEMISTRY 151
SAMPLE EXAM THREE
NOTE – This sample exam does not include questions from 16.5 & 16.6. These
sections WILL be on your exam!!
Check to be sure that you have 5 pages of exam (including this one). You must show all
of your work to receive credit! Partial credit will be given provided that I can follow
your work - be neat! Please do not hesitate to ask me any questions pertaining to the
wording of problems on the exam.
Kw = 1 x 10-14
Ka x Kb = Kw
Kw=[OH-][H3O+]
pH = -log[H3O+]
pH = pKa + log [Base]/[Acid]
pH + pOH = 14
CHEMISTRY 151
SAMPLE EXAM THREE
name ____________
student i.d.# __________
The following questions are worth 5 points each:
1) Which of the following statements are TRUE?
A) Dynamic equilibrium occurs when the rate of the forward reaction equals the rate
of the reverse reaction.
B) The equilibrium constant for the forward reaction is equal to the equilibrium
constant for the reverse reaction.
C) A reaction quotient (Q) larger than the equilibrium constant (K) means that the
reaction will favor the production of more products.
D) Dynamic equilibrium indicates that the amount of reactants and products are equal.
E) All of the above are true.
2) The equilibrium constant is given for one of the reactions below. Determine the value
of the missing equilibrium constant.
2SO2 (g) + O2 (g)
2 SO3 (g)
Kc = 1.7 x 106
SO3 (g)
1/2O2 (g) + SO2 (g)
Kc =?
3) Determine the value of Kc for the following reaction if the equilibrium concentrations
are as follows: [N2]eq = 3.6 M, [O2]eq = 4.1 M, [N2O]eq = 3.3 × 10−18 M
2 N2 (g) + O2 (g)
2 N2O (g)
4) Consider the following reaction at equilibrium. What effect will adding more SO3
have on the system?
SO2 (g) + NO2 (g)
SO3 (g) + NO (g)
A) The reaction will shift in the direction of products.
B) The reaction will shift to decrease the pressure.
C) No change will occur since SO3 is not included in the equilibrium expression.
D) The reaction will shift in the direction of reactants.
E) The equilibrium constant will decrease.
5) Consider the following reaction at equilibrium. What effect will increasing the
temperature have on the system?
Fe3O4 (s) + CO (g)
3FeO (s) + CO2 (g) ΔH˚ = + 35.9 kJ
A) The reaction will shift to the left in the direction of reactants.
B) The equilibrium constant will increase.
C) The equilibrium constant will decrease.
D) No effect will be observed.
E) The reaction will shift to the right in the direction of products.
6) Which of the following is a Bronsted-Lowry base?
A) CH4
B) HCN
C) NH3
D) Cl2
E) None of the above are Lewis bases.
7) Which of the following acids is the STRONGEST? The acid is followed by its Ka
value.
A) HF, 3.5 ×10−4
B) HCN, 4.9 ×10−10
C) HNO2, 4.6 ×10−4
D) HCHO2, 1.8 ×10−4
E) HClO2, 1.1×10−2
8) Which of the following acids (listed with pKa values) and their conjugate base would
be best to form a buffer with a pH of 8.10?
A) HC7H5O2, pKa = 4.19
B) HF, pKa = 3.46
C) HClO, pKa = 7.54
D) HCN, pKa = 9.31
E) HClO2, pKa = 1.96
9. Which of the following is a Lewis acid?
A) BCl3
B) CH4
C) NH3
D) CHCl3
E) None of the above are Lewis acids.
10) Which one of the following will form a basic solution in water?
A) KCl
B) LiCN
C) NaCl
D) MgBr2
E) All of the above will form basic solutions.
The following questions are worth 10 points each:
11) Determine the pH of a 0.461 M C6H5CO2H solution if the Ka of C6H5CO2H
is 6.5 ×10−5 .
12) Determine the pH of a 0.227 M C5H5N solution. The Kb of C5H5N is 1.7 ×10−9 .
13) A 1.00 L buffer solution is 0.150 M in HC7H5O2 and 0.250 M in LiC7H5O2.
Calculate the pH of the solution after the addition of 100.0 mL of 1.00 M HCl. The
Ka for HC7H5O2 is 6.5 ×10−5 .
14) When titrating a weak monoprotic acid with NaOH at 25°C, the
A) pH will be less than 7 at the equivalence point.
B) pH will be equal to 7 at the equivalence point.
C) pH will be greater than 7 at the equivalence point.
D) titration will require more moles of base than acid to reach the equivalence point.
E) titration will require more moles of acid than base to reach the equivalence point.
15) A 100.0 mL sample of 0.20 M HF is titrated with 0.10 M KOH. Determine the pH of
the solution after the addition of 100.0 mL of KOH. The Ka of HF is 3.5 ×10−4 .
TRIVIA: Which of the 50 states is nicknamed “The Granite State?”