CHEM 10123/10125, Quiz 6
April 18, 2012
Name_____________________
(please print)
Significant figures, phases, and correct units count, show charges as appropriate, and please box your answers!
1. (4 points) Write balanced, net ionic equations for the following half-reactions.
a. the anode reaction in the electrolysis of molten Fe2O3
2 O2–(l) O2(g) + 4e–
b. the cathode reaction in the electrolysis of aqueous NaOH
2 H2O(l) + 2e–  2 OH–(aq) + H2(g)
2. (5 points) Which of the following functional groups is not in the molecule below? Point out
and label the other functional groups.
a. amine, b. ester, c. alcohol, d. ketone, e. benzene ring
3. a. (1 point) Describe an advantage of a hydrogen-oxygen fuel cell compared to an ordinary
battery.
It lasts much longer
b. (1 point) Most batteries use redox reactions to supply power, however there is one type of cell
that uses ion transport between electrodes instead. This cell is called a lithium ion cell.
c. (4 points) The overall cell reaction for a rechargeable “nicad” battery is
Cd(s) + NiO2(s) + 2 H2O(l)  Ni(OH)2(s) + Cd(OH)2(s)
Write the balanced reduction half-reaction that occurs when the cell is recharged.
Cd (O H)2
(s)
+ 2e-
Cd ( S) + 2 O H-( a q )
4. (4 points) Define the relationship (if any) between each pair of molecules given below; i.e.
are the the same, structural isomers, geometric isomers, optical isomers, or do they have no
relationship?
OH
OH
H
C
HO
C
C C
H2
H3C
H
HO
and
H3C
a.
same
HO
N
O
NH
O
O and
d.
structural isomers
5. (5 points) A solution containing vanadium (MM = 50.942) in an unknown oxidation state
was electrolyzed with a current of 1.50 amps for 30.0 min. It was found that 0.475 g of V was
deposited on the cathode.
a. How many moles of electrons were consumed in the electrolysis?
b. How many moles of V were formed?
c. What was the oxidation state of the vanadium in solution?
5. (6 points) A potential of 0.142 V is recorded (under standard conditions) for a galvanic cell
constructed using the following half-reactions:
cathode: Pb2+(aq) + 2e–  Pb(s)
anode: Pb(s) + 2 Cl–(aq)  PbCl2(s) + 2e–
(a) What is the standard reduction potential for the anode reaction? [Eº (Pb2+/Pb) = –0.13 V]
Eº = 0.142 V = Eºred – Eºox = – 0.13 – Eºox
Eºox = – 0.27 V
(b) Calculate the solubility product, Ksp, for PbCl2.
PbCl2(s) ⇋ Pb2+(aq) + 2 Cl–(aq) Ksp = ?
Eº = (RT/nF)ln K = 0.142 V
ln Knet = 11.1
Knet = e11.1 = 7 x 104
Knet = 1/Ksp = 2 x 10–5
CHEM 10123/10125, Quiz 6
April 18, 2012
Name_____________________
(please print)
Significant figures, phases, and correct units count, show charges as appropriate, and please box your answers!
1. (4 points) Write balanced, net ionic equations for the following half-reactions.
a) the anode reaction in the electrolysis of molten LiBr
2 Br–(l)  Br2(l) + 2 e–
b) the cathode reaction in the electrolysis of aqueous KNO3
NO3–(aq) + 4 H+ + 3e–  NO(g) + 2 H2O(l)
2. (5 points) Which of the following functional groups is not in the molecule below? Point out
and label the other functional groups.
a. amine, b. ester, c. alcohol, d. ketone, e. ether
There is no ester in the molecule
3. a. (1 point) What by-product will come out of the exhaust pipe in a car that is powered by a
hydrogen-oxygen fuel cell?
Water vapor
b. (1 point) Describe an advantage of an alkaline battery compared to a cheaper dry-cell battery.
Longer lifetime b/c the basic supporting electrolyte doesn’t corrode
c. (4 points) The overall cell reaction for a rechargeable “nicad” battery is
Cd(s) + NiO2(s) + 2 H2O(l)  Ni(OH)2(s) + Cd(OH)2(s)
Write the balanced oxidation half-reaction that occurs when the cell is recharged.
2 OH–(aq) + Ni(OH)2(s)  NiO2(s) + 2e– + 2 H2O
4. (4 points) Define the relationship (if any) between each pair of molecules given below; i.e.
are the the same, structural isomers, geometric isomers, optical isomers, or do they have no
relationship?
H3C
HO
HO
a.
and
geometric isomers
H3C
C C
H
H
CH3 CH3
CH3
OH
OH
C
H2
CH2CH3
CH3CH2CCH2CHCH3
b.
same
C
CH3CCH2CHCH3
and
CH3 CH3
5. (5 points) A solution containing titanium (MM = 47.880) in an unknown oxidation state was
electrolyzed with a current of 0.750 amps for 2.00 hrs. It was found that 0.670 g of Ti was
deposited on the cathode.
a. How many moles of electrons were consumed in the electrolysis?
b. How many moles of Ti were formed?
c. What was the oxidation state of the titanium in solution?
6. (6 points) A potential of 0.146 V is recorded (under standard conditions) for a galvanic cell
constructed using the following half-reactions:
anode: Ag(s)  Ag+(aq) + e–
cathode: Ag2SO4(s) + 2e–  2 Ag(s) + SO42–(aq)
(a) What is the standard reduction potential for the cathode reaction? [Eº (Ag+/Ag) = +0.80 V]
Eº = 0.146 V = Eºred – Eºox = Eºred – (0.80)
Eºred = + 0.95 V
(b) Calculate the solubility product, Ksp, for Ag2SO4.
Ag2SO4(s) ⇋ 2 Ag+(aq) + SO42–(aq) Ksp = ?
Eº = (RT/nF)ln K = 0.146 V
ln K = 11.4
K = e11.4 = 9 x 104