Lecture 2, MWF 11:15 Day
The key to the
multiple-choice questions is given after the questions.
The
multiple-choice portion of this exam has 20 questions on 4 pages totaling 85
points. Be sure to include your name and 9 digit ID number on the answer sheet.
Lecture section 2 goes in column K. Blacken in all selections using a No. 2
pencil.
The
written portion of this exam has 4 questions totaling 15 points and is to be
done on the question sheet in the spaces provided. Be sure to fill in your name
and 9 digit ID number.
Turn in both the bubble
answer sheet and the hand written sheet. Keep the multiple-choice questions to check your
answers against the posted key.
Answers
to the questions will be posted on the web as soon as possible after the exam.
Information
for your use:
K = °C + 273
at 25 °C KW = 1.0 x 10-14 pH + pOH = 14
pH = -log [H3O+] pOH
= -log [OH-] pKa = -log Ka
Ka x Kb = Kw [H3O+] = Ka( [acid] / [conj base] )
Strong Acids: HCl, HBr, HI, HNO3,
HClO4, H2SO4 (Assume all other acids are
weak.)
Strong Bases: NaOH, KOH, Ba(OH)2
DH° = SDH°f (products) - SDH°f (reactants)
DSuniverse = DSsystem + DSsurroundings ³ 0
qp = DH
DS = qreversible /
T DSsurroundings = – DHsystem / T
DS° = SS°(products) - SS°(reactants)
1.
(5
points) If the pH of an aqueous 0.010 M
HNO2 solution is found to be 2.70, what is the value of Ka for this acid?
(A) 4.1 x 10-5 (B) 3.1 x 10-5 (C) 5.0 x 10-4 (D) 4.0 x 10-4 (E) 2.0 x 10-3
2.
(5 points) What is the [OH-] in a
0.50 M aqueous NH3 solution? Kb for NH3 is 1.8 x 10-5.
(A) 3.6 x 10-5 (B) 9.0 x 10-4 (C) 4.2 x 10-3 (D) 3.0 x 10-3 (E) 5.0 x 10-1
Use the Ka values for the
following weak acids as needed to answer questions 3 and 4.
HF Ka = 7.2 x 10-4 HCN
Ka = 4.0 x 10-10
3.
(4
points) What is the value of Kb for the equilibrium F- + H2O « HF + OH- ?
(A) 7.2 x 10-4 (B) 1.4 x 10-5 (C) 7.2 x 10-6 (D) 3.0 x 10-9 (E) 1.4 x 10-11
4.
(4
points) Which of the following would give the most basic 0.10 M aqueous
solution?
(A) NaF (B) NaCN (C) NaCl (D) HCl (E) NH4Cl
5.
(4
points) Which of the following would give an acidic aqueous solution?
(A) KNO3 (B) Ba(NO3)2 (C) Fe(NO3)3 (D) Na2CO3 (E) none would
Use the following
information for H2Se as needed for questions 6 and 7 :
H2Se + H2O « H3O+ + HSe- Ka1 = 1.7 x 10-4
HSe- + H2O « H3O+ + Se2- Ka2
= 1.0 x 10-10
6.
(5
points) What is the approximate [H3O+] in a 0.10 M
aqueous H2Se solution?
(A) 1.0 x 10-10 (B) 1.3 x 10-7 (C) 3.2 x 10-6 (D)
1.7 x 10-4 (E) 4.1 x 10-3
7.
(4
points) What is the [Se2-] in a 0.10 M aqueous H2Se
solution?
(A) 1.0 x 10-10 (B) 1.3 x 10-7 (C) 3.2 x 10-6 (D)
1.7 x 10-4 (E) 4.1 x 10-3
8.
(4
points) For the HSO3- ion, Ka = 6.4 x 10-8 and
Kb = 5.9 x 10-13. The pH of an
aqueous solution of NaHSO3
is expected to be
(A) less than 7
due to: HSO3-(aq) +
H2O(l) « SO32-(aq)
+ H3O+(aq)
(B) equal to 7
(C) greater than 7 due to: HSO3-(aq) + H2O(l) « H2SO3(aq) + OH-(aq)
(D) less than 7 due to: Na+(aq) + 2H2O(l) « NaOH(aq) + H3O+(aq)
(E) greater than
7 due to: Na+(aq) + H2O(l)
« NaH(aq) + OH-(aq)
9.
(4
points) Which of the following when added to 1 L of a 0.10 M HCl solution would
make the solution an effective buffer?
(A) 0.20 mol NaNO2 (C) 0.05 mol NaF (E) none of
them
(B) 0.10 mol NaCH3COO (D)
0.10 mol NaCl
10.
(4 points) When 1 L of pure water is added to
1 L of a 0.25M CH3COOH / 0.25M NaCH3COO buffer solution:
(A) the pH increases, but by less than one unit
(B) the pH increases by more than one unit
(C) the pH remains essentially constant
(D) the pH decreases, but by less than one unit
(E) the pH decreases by more than one unit
11.
(5 points) The solubility of PbI2
in water is 0.0013 M. What is the value of Ksp for PbI2 ?
(A) 2.6 x 10-3 (B) 1.6 x 10-5 (C) 1.7 x 10-6 (D)
5.1 x 10-7 (E) 8.8 x 10-9
12.
(4 points) Ksp for CuBr is 4.0 x 10-8 . What is the molarity of
Cu+ in a saturated solution of CuBr?
(A) 2.0 x 10-4 (B) 3.5 x 10-5 (C) 8.0 x 10-6 (D)
3.0 x 10-7 (E) 4.0 x 10-8
13.
(4
points) If solid sodium bromide were added to the solution in problem 12, the
solubility of CuBr would _____ and the value of Ksp would _____ .
(A) increase, increase (C) increase, not
change (E) increase, decrease
(B) decrease, decrease (D) decrease, not
change
Use the following Ksp's for
questions 14 and 15:
PbCl2 Ksp = 1.6 x 10-5 PbBr2 Ksp = 6.6 x 10-6 PbF2 Ksp = 3.7 x 10-8
14.
(5 points) If solid Pb(NO3)2
is added slowly to a solution that is 1.0 M in all three (Cl-, Br-
and F-) until the [Pb2+] is 1.0 x 10-5 M
(A) only a precipitate of PbCl2 will
form.
(B) only a precipitate of PbBr2 will
form.
(C) only a precipitate of PbF2 will form.
(D) precipitates of both PbBr2 and PbF2
will form.
(E) precipitates of PbCl2, PbBr2
and PbF2 will form.
15.
(5
points) What is the [Pb2+] needed to initiate precipitation of PbCl2
from a 0.40 M NaCl solution?
(A) 4.0 x 10-3 (B) 1.0 x 10-4 (C) 2.5 x 10-5 (D)
4.0 x 10-5 (E) 6.4 x 10-6
16.
(3
points) At constant pressure, the entropy of a substance must
(A) decrease as its temperature increases (D)
increase in a spontaneous process
(B) increase as its temperature increases (E)
be constant during a phase change
(C) decrease in a spontaneous process
17.
(4 points) The heat of vaporization of water
at its normal boiling point of 100 °C is 40.7 kJ/mol. What is
the value of DS in J/K for the process H2O(l) ® H2O(g) at 100 °C, 1 atm. ?
(A) 15.2 (B) -109 (C) 109 (D) -407 (E) 407
18.
(4 points) Predict which one of the following
reactions would have DSo > 0.
(A) 2HCl(g) ® H2(g) + Cl2(g) (D) NH3(g) + H2S(g) ® NH4HS(s)
(B) 2H2O2(l) ® 2H2O(l) + O2(g) (E) 2Mg(s) + O2(g)
®
2MgO(s)
(C) CH4(g) + 2O2(g) ® CO2(g) + 2H2O(l)
Questions 19 and 20 refer to
the following reaction and thermodynamic data at 298K.
NH3(g) +
HCl(g) ® NH4Cl(g)
DHof (kJ/mol) -46 -92 -314
So(J/mol K) 192 187 95
19.
(4
points) What is the standard entropy
change, DSo, for the reaction in J/K at 298K?
(A) 219 (B) -219 (C) 284 (D) -284 (E) 474
20.
(4
points) If one mole of NH4Cl(s) is formed under standard conditions,
what is the entropy change for the surroundings
in J/K at 298K?.
(A) 176 (B) -176 (C) 284 (D) -591 (E) 591
The following list gives the number of points for each answer, in the order ABCDE, for each question. The correct answer to each question is the one worth the most points.
1 00530
2 00050
3 00004
4 34000
5 00400
6 00005
7 40000
8 40200
9 40000
10 00400
11 00005
12 40000
13 02040
14 00052
15 05200
16 03000
17 00400
18 04000
19 00240
20 00024