Chemistry 106: General Chemistry II
Dr. Gutow and Dr. Matsuno
Page 1
Exam 3 Form A
Fall 2004
1) Name ____________________________________
You are to keep this copy of the test. Your name is in case you leave it behind.
2) Use only a #2 pencil on the answer sheet.
3) Before starting the exam fill in your student ID# (not your SS#). Also fill in your name, course number and sign the
form.
4) Fill in the test form section (A, B, C or D). Which form you have is shown in the upper right corner.
5) Do not begin the exam until you are told to.
6) You will not get your scan sheet back!!! Circle your answers on this exam sheet and then transfer them to the scan
sheet when you are satisfied with all your answers. An answer key will be posted on the class web site and in the
glass case across from the lab after the exam.
7) If atomic weights are needed use only those from the attached periodic table.
8) No scratch paper is to be used. Use the back of this exam sheet if necessary.
9) There are 35 equally weighted questions on this exam. You have 90 minutes to complete them.
10) If you believe there is more than one correct answer pick only the best answer.
Useful Data
Constants
density of H2 O = 1.00 g/mL
NA(Avogadro’s #) =6.022 x 102 3 particles•mol-1
R (gas constant) = 8.315 J•mol-1•K-1
R(gas constant) = 0.8206 L•atm•mol-1•K-1
KW = 1.00 x 10-14
Equations
% = fraction • 100 %
ppm = fraction • 106 ppm
T (in Kelvin) = 273.15 + T (in ˚C)
T (in Celsius) = (5/9) (T (in F) -32)
Rate = kf [A]m[B]n for aA+bB--> cC+dD
Κ = exp(-∆Go /{RT})
Units
2.54 cm = 1 inch
3.78 L = 1 gal
1 kg = 2.20 lb
1 % = 10,000 ppm
1 hr = 60 min
1 min = 60 seconds
1 amu = 1.660540 x 10-27 kg
molarity (M) = moles solute/L sol’n
molality (m)= moles solute/ kg solvent
ΔGo = -RT ln K
ΔG = ΔGo + RT ln K
K = kf / kr
lnK = (-ΔHo /R)(1/T) + ΔSo /R
ln(K2 /K1 ) = (-ΔHo /R)(1/T2 - 1/T1 )
pH = pKa + log([base]/[acid])
pH = -log [H+]
pH + pOH = pKw and KW = KaKb
Ks p= (mmxx )s(m+x)
Ktot = (K1 )m(K2 )n . . .
x=
-b!
b2 - 4ac
2a
Chemistry 106: General Chemistry II
Dr. Gutow and Dr. Matsuno
Page 2
Exam 3 Form A
Fall 2004
1. Choose the statement that best describes the situation at equilibrium in a chemical reaction.
a. stops completely.
b. stops and the reverses
c. continues in the forward direction and the reverse reaction at the same rate.
d. reverses
e. none of the above
2. The chemical equilibrium
2A
B
has a forward rate constant, kf = 10 M-1sec-1 and a reverse rate constant kr = 5 sec-1. What is the rate of the
reverse reaction? (Rr is a rate of reverse reaction.)
a. Rr = kr
b. Rr = kr[B]
c. Rr = kr[B][A]2
d. Rr = kr[B]/[A]2
e. Rr = kr[A]2
3. Identify the equilibrium expression for the reaction below:
boy + girl
couple.
a. K = [boy][girl]/[couple]
b. K = [boy] + [girl]/[couple]
c. K = k[boy][girl][couple]
d. K = [couple]/[boy][girl]
e. K = k[boy]/girl]
4. If the reaction quotient Q has a smaller value than the related equilibrium constant K
a. the reaction is at equilibrium
b. the reaction will continue to make more products.
c. the reaction will consume products and make reactants.
d. the reaction will release heat to achieve equilibrium.
e. the reaction always generates heat.
5. The equilibrium constant for the formation of calcium carbonate
from the ions in solution is 2.2 x 108 according to the reaction
Ca2+(aq) + CO3 2-(aq)
? CaCO (s)
3
What is the value of equilibrium constant for the reverse of this reaction?
a. 1.2 x 108
b. -2.2 x 108
c. 2.2 x 10-8
d. 4.5 x10-9
e. -4.5 x 10-9
Chemistry 106: General Chemistry II
Dr. Gutow and Dr. Matsuno
Page 3
Exam 3 Form A
Fall 2004
6. The equilibrium constants for two reactions are known:
Mm++ 4LHL
[ML4]m-4
Ka
H+ + L-
Kb
What must be the value of the equilibrium constant, Kt for the total reaction shown below?
Mm+ + 4HL
[ML4]m-4 + 4H+
Kt
a. KaKb
b. Ka + 4Kb
c. Ka + Kb 4
d. Ka4Kb
e. KaKb 4
7. If K for a reaction is large
a. ΔHº is definitely negative.
b. ΔGº is definitely negative.
c. ΔHº is definitely positive.
d. ΔGº is definitely positive.
e. ΔGº = ΔHº + TΔSº
?
8. In a simple equilibrium A + B
C, will there be any stress to the system if both B and C are added to the
equilibrium system simultaneously and in the same amount?
a. No, these two stresses will cancel each other out.
b. No, these stresses are added simultaneously.
c. Yes, with no addition of A, the system will be under stress; but if A were also added, then there would be no
stress since all the stresses would cancel.
d. Yes, A is involved in the equilibrium, too, and the ideal ratio of B to C may be far from 1:1.
e. It really depends on what kind of chemicals B and C are.
9. An effective catalyst for a particular reaction is added to that reaction at equilibrium. What must happen to the
equilibrium?
a. More products will be generated by reducing the activation energy.
b. The new equilibrium will be reached very quickly.
c. The catalyst will be poisoned become unfunctional.
d. nothing
e. a and b
10. The equilibrium constant for the acid ionization of mercaptoethanol is 1.91 x 10-10
HSCH2CH2OH(aq)
H+ (aq) + SCH2CH2OH-(aq)
A solution of mercaptoethanol in water is _________
a. almost entirely ionized.
b. almost entirely un-ionized.
c. about one-half ionized.
d. a strong acid.
e. an ether.
Chemistry 106: General Chemistry II
Dr. Gutow and Dr. Matsuno
Page 4
Exam 3 Form A
Fall 2004
11. The sulfide ion, S2-, reacts with water as a weak base:
S2- + H2O
SH- + OH-
with an equilibrium constant of 1.0. If sodium sulfide were dissolved in water to make a solution of 0.50 M, what
would the resulting concentration of OH- be?
a. 0.50 M
b. 0.37 M
c. 0.63 M
d. 1.0 M
e. 0.73 M
12. In the Initial (I), Change (C) and Equilibrium (E). table just started for calculation of equilibrium concentrations of
the reaction shown at the top, the terms in the change column are
M2+
+
4L
I 0.10 M
C ______
E etc.
0.32 M
______
[ML4]2+
0
_______
a. +x, +x, +x
b. -x, -x, +x
c. -x, -4x, +x
d. +x, +4x, +x
e. -4x, -x, +4x
13. What is the value of the equilibrium constant at 500 K for a chemical equilibrium that has a ΔHº value of 250
kJ/mole and a ΔSº value of 48 J/K-mole?
a. 2.45 x 10-24
b. –3.01 x 104
c. –54.36
d. 4.22 x 102 8
e. 5.21
14. Given the two measurements below, calculate ΔHº.
T, ºC
K
15
25
2.6 x 103
9.3 x 104
a. 255 kJ/mol
b. –271 kJ/mol
c. 3250 kJ/mol
d. –3250 kJ/mol
e. 55 kJ/mol
Chemistry 106: General Chemistry II
Dr. Gutow and Dr. Matsuno
Page 5
Exam 3 Form A
Fall 2004
15. The reaction of nitrogen gas with hydrogen gas, shown below has a Kp value of 6.9 x 10-5 for partial pressures in
atmospheres. If a closed vessel was charged with 20. atm each of of H2 and N2 , what would be the equilibrium
partial pressure of N2 H4 (g)?
N2 (g) + 2H2 (g)
?
N2 H4 (g)
KP = 6.9 x 10-5
a. 2.8 x 10-2 atm
b. 20. atm
c. 0.55 atm
d. 1.4 x 10-3 atm
e. 1.8 atm
16. In equilibrium expressions, solids and solvents are ignored because they
a. are not necessary for the reaction.
b. have the assigned value of zero.
c. have constant values, Ks and Kl .
d. are treated with different rate constants
e. do not change concentration.
17. Ka implies the following reaction (where HA is a weak acid):
a. HA + OH
b. HA + H2O
H2O + AH3O+ + A-
+
c. HA + H3O
H2A+ + H2O
+
d. HA + H2A
e. all of the above
H2A+ + HA
18. The concentration of [A-] resulting from monoprotic weak acid dissociation
a. is the same as the concentration of [H+] resulting from monoprotic weak acid dissociation.
b. is less than the concentration of [H+] resulting from monoprotic weak acid dissociation.
c. is the same as the concentration of [HA].
d. is greater than the concentration of [H+] resulting from monoprotic weak acid dissociation.
e. is unrelated to the concentration of [H+] resulting from monoprotic weak acid dissociation.
19. The degree of dissociation of HCl, HNO3 or the first proton of H2 SO4 is
a. dependent on the total concentration of the acid.
b. between 1 and 10%.
c. between 10 and 100%.
d. 100%.
e. They are covalently bonded, so it is 0%
Chemistry 106: General Chemistry II
Dr. Gutow and Dr. Matsuno
Page 6
Exam 3 Form A
Fall 2004
20. In the Brønsted-Lowry model of acids and bases, an acid
a. is a proton donor.
b. is a proton acceptor.
c. is a electron acceptor
d. is a electron donor
e. is at equilibrium
21. Ammonia, NH3 , is a weak base in aqueous solution. What is the acid that reacts with this base in an aqueous
solution containing ammonia as the only solute?
a. There are no acids present or required.
b. water
c. NH4 +
d. There are no acids present, so ammonia does not act as a base in this situation.
e. NH3 is actually an acid in this case.
22. The equilibrium constant Kb describes the following reaction for a weak base, B, in aqueous solution:
?
?
?
?
?
a. B + H+
BH+
+
b. B + H + H2 O
BH+ + H2 O
c. B + H2 O
BH+ + OHd. B + OH
BH- + O2e. B + 2OH
BH+ + H2 O
23. In the following reaction, which pair is the acid reactant and its conjugate base product?
CH3COOH + NH3
CH3COO- + NH4+
a. CH3 COOH and CH3 COOb. CH3 COOH NH3
c. CH3 COOH and NH4 +
d. NH3 and CH3 COOe. NH3 and NH4 +
24. Kw is related to
a. [H3 O+] [OH-].
b. 1.0 x 10-14 at 25º C.
c. 2H2 O
OH- + H3 O+
d. a, b, and c
e. none of the above
?
25. In the pH scale, [H+] changes
a. from 1 M to 14 M.
b. by a factor of 10 for each pH unit.
c. by a factor of "e" for each pH unit.
d. from -1 to -14 M.
e. both a and b
Chemistry 106: General Chemistry II
Dr. Gutow and Dr. Matsuno
Exam 3 Form A
Fall 2004
Page 7
26. When [H+] = 4.0 x 10-9 M in water at 25° C,
a. pH = 9.40.
b. pH = 7.00.
c. pH = -8.40.
d. pH = 8.40.
e. pH = 7.3
27. Water vapor in automobile exhaust sometimes condenses in the tailpipe in cold weather. This water is probably
a. neutral because distilled water is always neutral.
b. acidic because of the presence of NOx and CO2 in vapor.
c. basic because the water vapor is exposed to a catalytic converter.
d. deuterated because the water vapor is a while steam.
e. dissociated because of the condensation.
28. A solution with a pOH of 4.3 has a [H+] of
a. 6.8 x 10-9 M.
b. 3.2 x 10-4 M.
c. 4.8 x 10-5 M.
d. 2.0 x 10-10 M.
e. 5.0 x 10-5 M.
29. Phosphoric acid is a triprotic acid, ionizing in the following sequential steps:
H3PO4 + H2O
H2PO4- + H2O
HPO42 + H2O
H2PO4- + H3O+
HPO42- + H3O+
PO43- + H3O+
Ka1
Ka2
Ka3
What is the value of Kb for the base sodium phosphate?
a. Ka3
b. 1/Ka3
c. Kw/Ka3
d. Kw∗Ka3
e. Kw/Ka2
30. The stronger the acid,
a. the stronger its conjugate base.
b. the weaker its conjugate base.
c. the more concentrated the acid.
d. the less concentrated the conjugate base.
e. the stronger the proton
31. A solution that contains a weak acid and its conjugate base in roughly equal concentrations is
a. neutralized.
b. a half-acid solution.
c. a buffer.
d. a mixture.
e. all of the above
Chemistry 106: General Chemistry II
Dr. Gutow and Dr. Matsuno
Page 8
Exam 3 Form A
Fall 2004
32. What is the pH of a 100-mL solution made from 46.2 mL of 0.050 M nitric acid and water?
a. 1.64
b. 1.30
c. 1.33
d. 2064
e. 7.00
33. In a buffer solution in which [HA] = [A-],
a. pH = 1
b. pH = Ka
c. pH = pKa
d. pOH = pKa
e. pH = pKw
34. If you make a solution in water which contains 0.100 M KHSO3 and 0.050 M H2 SO3 what will its pH be? Useful
acid base equilibria and their associated Ka and pKa are listed below:
RXN
Ka
pKa
H2 SO3
H+ + HSO3 1.3 x 10-2
1.89
HSO3 H+ + SO3 26.2 x 10-8
7.21
HC2 H3 O2
H+ C2 H3 O2
1.76 x 10-5
4.75
?
?
?
a.
b.
c.
d.
e.
7.51
1.59
1.89
6.91
2.19
35. What is the approximate solubility of barium sulfate in a solution containing 0.050 M sodium sulfate? The Ks p
value for barium sulfate is 1.1 x 10-10.
a. 7.4 x 10-6
b. 5.5 x 10-11
c. 1.0 x 10-5
d. 2.2 x 10-9
e. 5.5 x 10-12