Name _____________________________ SSN ______________________________
CHEMISTRY 212, Lect. Sect. 002
Dr. G. L. Roberts
Exam #3
1.
Amphoteric hydroxides dissolve in both highly acidic and highly basic solutions.
(a) true
2.
(b) false
The solubility of an ionic solid is decreased when a common ion is present in solution.
(a) true
4.
(b) false
The magnitude of the ratio of Qsp/Ksp is used to predict whether an ionic solid will precipitate.
(a) true
3.
Thursday, April 20, 2000
(b) false
Indicate the major chemical species present in a solution of 0.10M NH3 and 0.10M NH4Cl.
(a) NH3, NH4+
(b) NH3, NH4+, Cl−
(c) NH3, NH4+, Cl−, OH−
(d) NH3, NH4+, Cl−, OH−, H2O
5.
What is the pH of a solution prepared by mixing 25.00mL of 0.10M CH3COOH with 25.00mL
of 0.050M NaCH3CO2? Assume that the volumes of solution are additive and that the Ka for
acetic acid is 1.8 x 10−5.
(a) 2.22
6.
(c) 4.74
(d) 4.44
In general, the more atoms of a given type present in a molecule, the lesser the capacity to take
up energy and thus the lower the entropy.
(a) true
7.
(b) 2.87
(b) false
Which of the following statements is not true?
(a) ∆H - T∆S < 0, then rxn is spontaneous as written
(b) ∆H - T∆S > 0, rxn is not spontaneous
(c) ∆H - T∆S = 0, rxn is at equilibrium
(d) none of the above
8.
Which of the following combinations of chemicals could be used to make a buffer solution?
(a) HCl/NaOH
9.
(b) NaOH/NH3
(c) HCl/H3PO4
(d) HCl/NH3
Which statement about buffers is true?
(a)
(b)
(c)
(d)
Buffers have a pH=7
Buffers consist of a strong acid and its conjugate base
A buffer does not change pH on addition of a strong acid or strong base
Buffers resist change in pH upon addition of small amounts of strong acid or strong base
10.
What is W in Boltzmann's formula, S=k ln W?
(a) a fraction indicating the probability of obtaining a result
(b) a random number
(c) the work times Avogadro's number
(d) the number of ways of obtaining the state
11.
The total entropy of a system and its surroundings always increases for a spontaneous process.
This is a statement of
(a) the law of constant composition
(c) the third law of thermodynamics
12.
TRIS {(HOCH2)3CNH2} is one of the most common buffers used in biochemistry. A solution
is prepared by adding enough TRIS and 12M HCl (aq) to give 1.00 liter of solution with
[TRIS]=0.30 M and [TRISH+]=0.60 M. What is the pH of this buffered system if the pKb is
5.92?
(a) 8.08
13.
(b) 5.92
(c) 6.22
(d) 7.78
Calculate the solubility of iodate if copper(II) iodate is dissolved in water and the value of Ksp =
7.4 x 10−8M3 at 25°C .
(a) 7.4 x 10−3M
14.
(b) the first law of thermodynamics
(d) the second law of thermodynamics
(b) 2.6 x 10−3M
(c) 1.3x10−3M
(d) 5.2x10−3M
The emf of the following cell at 25°C is 0.475V. What is the pOH of the test solution?
1
Name _____________________________ SSN ______________________________
(a) 4.8
15.
ZnZn2+ (1 M) H+(aq, test solution)  H2 (1 atm) Pt
(b) 9.6
(c) 4.4
(d) 9.2
(e) 8.8
What is the percent dissociation of ascorbic acid if the solution has a pH = 5.50 and a
pKa=4.10?
(a) 96%
16.
(b) 10%
(c) 5%
(d) 1%
What is the characteristic pH-titrant curve for the titration of a strong acid by a strong base?
pH
titrant (A)
17.
titrant (B)
titrant (C)
titrant (D)
−4
Formic acid (HCOOH, Ka=1.8 x 10 ) is the principal component in the venom of stinging ants.
What is the molarity of the formic acid solution if 25.00mL of aqueous formic acid required
29.80mL of 0.0567M NaOH to reach the equivalence point?
(a) 0. 0676M
(b) 0.0567M
(c) 0.0476M
(d) 0.0134 M
18.
Which of the following metal hydroxides are amphoteric?
(a) Al(OH)3, Zn(OH)2, Cr(OH)3, Sn(OH)2
(b) Cu(OH)2, Mn(OH)2, Fe(OH)2, Fe(OH)3
(c) Be(OH)2, Ca(OH)2, Ba(OH)2, Sr(OH)2
(d) LiOH, NaOH, KOH, RbOH
19.
Which of the following gas molecules has the greatest standard molar entropy at 25°C?
(a) H−C≡C−H
20.
(b) ∆G = Kp/Qp
(d) ∆G = RTln(Kp/Qp)
For a cell reaction based on the following half-reactions, how many moles of lead are oxidized
by one mole of Cr2O72−?
Cr2O72− (aq) + 14 H+ (aq) + 6e− → 2 Cr3+ (aq) + 7 H2O (l)
Pb(s) → Pb2+ (aq) + 2e−
(b) 2
(c) 3
(d) 6
The iron content of foods can be determined by dissolving them in acid (forming Fe3+),
reducing the iron(III) to iron(II), and titrating with cerium(IV). Fe2+ (aq) + Ce4+ (aq) → Fe3+
(aq) + Ce3+ (aq). Identify the two half-reactions in the above reaction.
Oxidation half-reaction
(a)
(b)
(c)
(d)
24.
(c) ∆G = RTln(Qp/Kp)
∆G° = −332 kJ; the equilibrium composition should favor products
∆G° = −332 kJ; the equilibrium composition should favor reactants
∆G° = −166 kJ; the equilibrium composition should favor products
∆G° = −166 kJ; the equilibrium composition should favor reactants
(a) 1
23.
(d) all have the same entropy
Consider the reaction: N2(g) + F2(g) → NF3(g) ∆H° = −249kJ and ∆S° = −278J/K at 25°C.
Calculate ∆G° and state whether the equilibrium composition should favor reactants or products
at standard conditions.
(a)
(b)
(c)
(d)
22.
(c) H3C−CH3
What is the relationship between ∆G, Qp, and Kp for a reaction involving gases?
(a) ∆G = Qp/Kp
21.
(b) H2C=CH2
Fe2+ (aq) + e− → Fe3+ (aq)
Ce4+ (aq) + e−→ Ce3+ (aq)
Fe2+ (aq) →Fe3+ (aq) + e−
Ce4+ (aq) → Ce3+ (aq) + e−
reduction half-reaction
Ce4+ (aq) → Ce3+ (aq) + e−
Fe2+ (aq) →Fe3+ (aq) + e−
Ce4+ (aq) + e−→ Ce3+ (aq)
Fe2+ (aq) + e− → Fe3+ (aq)
For the galvanic cell Pt(s)|Sn2+(aq), Sn4+(aq)|| Pb2+(aq) |Pb(s), what is the function of the Pt(s)?
(a)
(b)
(c)
(d)
Pt is the anode and is a reactant in the overall cell reaction
Pt is the cathode and is a product in the overall cell reaction
Pt is the anode and does not appear in the overall cell reaction
Pt is the cathode and does not appear in the overall cell reaction
2
Name _____________________________ SSN ______________________________
What is the relation between ∆G° and E° for the cell reaction below?
Ni2+(aq) + Cd(s) → Cd2+(aq) + Ni(s)
25.
(a) ∆G° = FE°
(b) ∆G° = 2 FE°
(c) ∆G° = −FE°
(d) ∆G° = −2FE°
Given PH2 = 0.100 atm, [Cd2+] = 0.200M, and [H+] = 1.00 x 10−5M, calculate E at 25°C for a
cell based on the reaction: Cd(s) + 2H+(aq) → H2(g) + Cd2+(aq) E° = +0.40V.
26.
(a) −0.15V
27.
(b) −0.30V
(c) +0.30V
(d) +0.15V
How long must a 50.0 A current be passed through an electrolytic cell for refining copper to
produce 3.00 moles of copper?
(a) 1.50 hours
(b) 1.61 hours
(c) 2.50 hours
Key equations
K.E. = mv2/2
me = 9.11 x 10-31 kg
mp = 1.673 x 10-27 kg
mn = 1.675 x 10-27 kg
J = N•m
J = C•V
F = 96,500 C
N = m•kg•s-2
R= 0.0821 L•atm/mol•K
R= 8.314 J/mol • K
1 L•atm = 101 J = 0.101 kJ
1 Pa = 1 kg/(m• s2) = 1 N/m2
1 atm = 1.01 x 105 Pa
g = 9.807 m/s2
w = -P∆V
∆U = q + w
∆H°rxn = Σ∆Hf°(products) - Σ∆Hf°(reactants)
∆Hrxn = ∆Urxn + P∆V
∆H = nCp∆T
∆H = cp∆T
q = ms∆T
1 Ci = 3.700 x 1010 dps
t1/2 = 5730 years for 14C
 ni   Pi 
= 

 n total   Ptotal 
xi = 
 P2   ∆H vap   1
1
 − 
 =
 P1   2.303R   T1 T2 
log 
0
 1 1 
 K 2   ∆H rxn
 − 
 =
ln 
 K1   R   T1 T2 
S = kHP
P A = P oA X A
∆P = P oA X B
∆Tb = Kbcm
∆Tf = Kfcm
π = MRT
[ A]t
= −kt
[ A]0
[ A]t
= −kt/2.303
log
[ A]0
ln
 k2 
Ea  1 1 
 =
 − 
 k 1  2.303R  T1 T2 
log 
(d) 3.22 hours
t1/2 = 0.693/k
k = pfZ
f = e-Ea/RT
r.m.s. =
3RT
Mm
[ C ] c [ D] d
[ A]a [ B]b
[ C ]i c [ D] i d
Qc =
[ A]i a [ B]i b
Kc =
Kp = Kc(RT)∆n
[ H3O + ]2 [ S 2 − ]
K=
[ H2 S ]
wmax = -nFEcell
E0cell = E0cathode - E0anode
∆G0 = -nFE0cell
∆Grxn = ∆G0rxn + RTlnQ
∆G0rxn = -RT lnK
∆Grxn = RTln(Q/K)
E0cell = (0.0592/n)log K
Ecell = E0cell -(0.0592/n)logQ
Q = It
∆Sfus = (∆Hfus/Tm)
3