1 General Chemistry II Jasperse Electrochemistry. Electrochemistry . Extra Practice Problems Oxidation Numbers Balancing Redox; Electrons Transferred; Oxidizing Agents; Reducing Agents
p1 p2
Free Energy and Equilibrium K Values and Voltage
p10 p11
Spontaneous Voltaic Electrochemical Cells Cell Potentials Predictable Oxidation and Reduction Strength Patterns Ranking Relative Activity, Based on Observed Reactivity or Lack Thereof
p4 p5 p8 p9
Nonstandard Concentrations and Cell Potential Electrolysis
p11 p12
Answer Key
p13
Key Equations Given for Test:
E˚cell=E˚reduction + E˚oxidation
G˚ ! G˚
= –96.5nE˚cell (! G˚ G˚ in kJ)
Ecell = E˚ – [0.0592/n]log Q
log K = nE˚/0.0592
Mol e – = [A • time (sec)/96,500]
time (sec)= mol e • 96,500/current (in A)
t = (t1/2/0.693) ln (Ao/At)
ln (Ao/At) = 0.693•t /t1/2
E = ! mc mc2 (m in kg, E in J, c = 3x108 m/s)
Oxidation Numbers 1.
chromium in the ionic compound ammonium dichromate, (NH 4)2Cr 2O7? What is the oxidation number of chromium in a. b. c.
2.
+6 +7
+3 +4 +5
d. e.
+6 +7
What are the oxidation numbers for nickel, sulfur, and oxygen in oxygen in Ni2(SO4) 3? a. b. c.
4.
d. e.
What is the oxidation number of carbon in carbon in the ionic compound potassium carbonate, K 2CO3? a. b. c.
3.
+3 +4 +5
Ni +3; S +6; O -2 Ni +2; S +4; O -2 Ni +3; S +4; O -2
d. e.
Ni +2; S +2; O -2 Ni +2; S +4; O -1
When hydrogen reacts with calcium metal, what are the oxidation numbers of the calcium and hydrogen in the CaH 2 product? s) + H2( g ) ! CaH2( s) Ca( s
a. b. c. 5.
–2 and +1 +1 and –2 +2 and –1
d. e.
0 and 0 +2 and –2
What are the original and final oxidation numbers for iron in the smelting of iron from iron oxide? s) + 3CO( g g ) ! 2Fe( s) + 3CO2( g ) Fe2O3( s
a. b. c.
+2 ! 0 +3 ! 0 0 ! +2
d. e.
+6 ! 0 No change
2 Balancing Redox; Electrons Transferred; Oxidizing Agents; Reducing Agents 6.
Balance the following reaction. How many electrons are transferred?
Mg +
a. 7.
3
b.
4
O2 !
c.
MgO
6
d.
8
e.
2
Methanol fuel cells use the following reaction. How many electrons are transferred in this redox reaction as written?
2CH3OH + 3O2 ! 2CO2 + 3H2O
a. b. c. 8.
3 6 8
d. e.
What is the coefficient for hydroxide, and how many electrons are transferred after balancing the reaction? 2-
Pb(OH)4
a. b. c.
9.
12 2
+
-
ClO
!
-
2 OH and 2 electrons 3 OH and 4 electrons 1 OH and 2 electrons
PbO2 +
d. e.
-
-
Cl +
OH +
H2O
-
2 OH and 4 electrons None of the above
Cobalt is one of many metals that can be oxidized by nitric acid. Balance the following the reaction. How many electrons are transferred, and what would be the coefficient for H 2O in the balanced reaction? Co +
a. b. c.
–
NO3 +
+
H
!
NO +
3 electrons; 2 H2O 6 electrons; 6 H 2O 4 electrons; 2 H2O
d. e.
H2O +
2+
Co
6 electrons; 4 H2O None of the above
10. What was oxidized and what was reduced in the following reaction? 2Hg2+ +
a. b. c.
+
Hg was oxidized; N 2H4 was reduced 2+ Hg was reduced; N 2H4 was oxidized 2+ Hg was oxidized; N 2H4 was oxidized
N2H4
!
d. e.
2Hg + N2 +
+
4H+
Hg was reduced; N 2H4 was reduced None of the above
3 11. The following reaction occurs in basic solution. Identify the oxidizing agent. Note the reaction equation is not balanced. – – 2– H2O(l) + Zn( s) + NO3 (aq) + OH (aq) ! Zn(OH)4 (aq) + NH3(aq)
a. b. c.
Zn( s) – NO3 (aq) (the nitrogen) – OH (aq)
d. e.
H2O(l) (the oxygen) NH3(aq) (the nitrogren)
12. For the following reaction, which statement, A–D, is not correct? If more than one is not correct, respond E. –2
2Au + 4Cl2 ! 2AuCl4
a. b. c.
Au is the reducing agent. Cl2 is the oxidizing agent Au is oxidized.
d. e.
The equation is fully balanced. More than one statement is not correct.
13. Which substance is the reducing agent in the following reaction? 2+ Ca( s) + Zn (aq)
a. b. c.
Ca( s) 2+ Zn (aq) 2+ Ca (aq)
!
d. e.
2+ Ca (aq) + Zn( s)
Zn( s) None of the above
14. Which substance is the reducing agent in the following reaction? +
4H (aq)
a. b. c.
+
H (aq) Cl (aq) MnO2( s)
-
+ 2Cl (aq) + MnO2( s)
d. e.
!
2+
Cl2( g ) + Mn (aq) + 2H2O(l )
Cl2( g ) 2+ Mn (aq)
15. Which one of the following items does not characterize an oxidizing agent? a. b. c. d. e.
An oxidizing agent gains electrons. An oxidizing agent causes another species to be oxidized. The oxidation number of an oxidizing agent decreases. 7+ A good oxidizing agent is a metal in a high oxidation state, such as Mn . An example of a good oxidizing agent is an alkali metal, such as Na.
16. Which of the following statements about electrochemical cells is true? a. b. c. d. e.
Reduction occurs at the anode An element with a high love for electrons is l ikely to be easily oxidized Oxidation occurs at the anode Only oxidation half–reactions are useful none of the above
4 Spontaneous Voltaic Electrochemical Cells 17. Which statement about a voltaic cell is not correct? a. b. c. d. e.
Chemical species can have their oxidation number decreased at the cathode. Reduction occurs at the cathode. Usually the cathode is a metal strip. Oxidation occurs at the anode. Elemental metal is routinely converted to metal cations at the cathode
18. Which statement regarding voltaic cells is not correct ? a. b. c. d. e.
Reduction occurs at the cathode. Anions move through the barrier/bridge toward t he electrode where oxidation is occurring. The electrode where reduction is occurring is represented by a positive sign. Electrons flow in the external circuit from the cathode to the anode. Electrons flow in the external circuit toward the electrode represented by a positive sign.
19. A voltaic cell is constructed based on the oxidation of zinc metal and the reduction of silver cations. Solutions of silver nitrate and zinc nitrate also were used. Locate the silver and the silver nitrate on the diagram.
a) b) c) d)
silver = b; silver nitrate = a silver = d; silver nitrate = b silver = d; silver nitrate = c silver = d; silver nitrate = a
20. A voltaic cell is constructed based on the oxidation of zinc metal and the reduction of silver cations . Solutions of silver nitrate and zinc nitrate also were used. Locate the zinc nitrate on the diagram, and identify the anode .
a) b) c) d)
Zinc nitrate = a; anode = d Zinc nitrate = a; anode = Zinc Zinc nitrate = c; anode = d Zinc nitrate = c; anode = Zinc
21. A voltaic cell is constructed based on the oxidation of zinc metal and the reduction of silver cations. Solutions of silver nitrate and zinc nitrate also were used. Which statement is true regarding the direction of electron flow through the external wire?
a) b) c) d)
Electrons flow from left to right, from the Zinc Electrons flow from right to left, to the Zinc The zinc electrode will get larger as more zinc forms. Anions will flow through the “bridge” from the zinc side to the silver side +
2+
22. For the cell shown, the standard reduction potentials are +0.80 V for Ag and –0.76 V for Zn . Based on the reduction potentials, the electrode is where the reduction will occur and it is called the . voltmeter
a. b. c. d. e.
Ag, cathode Ag, anode Zn, cathode Zn, anode none of the above
wire salt bridge
Ag
1M Ag+
1M Zn 2 +
Zn
5 Cell Potentials 23. What is E˚ for the following balanced reaction? 2+ 2+ Zn( s) + Pb (aq) ! Zn (aq) + Pb( s)
Half-reaction
Standard Reduction Potential
2+ – Zn (aq) + 2e ! Zn( s) 2+ – Pb (aq) + 2e ! Pb( s)
a. b. c.
–0.763 –0.126
+0.637 V –0.637 V +1.274 V
d. e.
–0.889 V +0.889 V
24. What is E˚ for the following balanced reaction? 3+ 3+ Al( s) + Fe (aq) ! Al (aq) + Fe( s)
Half-reaction
Standard Reduction Potential
3+ – Fe (aq) + 2e ! Fe( s) 3+ – Al (aq) + 2e ! Al( s)
a. b. c.
+0.771 –1.660
+1.280 V –2.431 V +2.431 V
d. e.
–0.889 V +0.889 V
25. What is E˚ for the following balanced reaction? + 3+ 4H (aq) + Fe( s) + NO3 (aq) ! Fe (aq) + NO(aq) + 2H2O(l)
– NO3 + 3+
+
–
4H + 3e Fe + 3e – ! Fe
a. b. c.
! NO
+0.189 V –0.189 V +1.731 V
d. e.
+ 2H 2O
Standard Reduction Potential E˚ = +0.960 V E˚ = +0.771 V
–1.731 V None of the above
26. Given the electrochemical reaction shown, if the standard reduction potential of Ag 2+ standard reduction potential of Cu ! Cu is +0.34V, what is E˚ for the following? 2+
+
Cu / Cu (aq) // Ag (aq) / A a. b. c. d. e.
! Ag
is +0.80 V, and the
E˚ = ??? V
+1.26 V +0.85 V +0.46 V -0.37 V none of the above
27. Given the electrochemical reaction shown, if the standard reduction potential of Ni 3+ standard reduction potential of Al ! Al is -1.66V, what is E˚ for the following? Al / Al 3+(aq) // Ni+2(aq) / Ni a. b. c. d. e.
+
+1.26 V +0.85 V +0.46 V +1.40 V none of the above
+2
! Ni
E˚ = ??? V
is -0.26 V, and the
6 28. Given the electrochemical reaction shown, if the standard reduction potential of Zn standard reduction potential of Mg 2+ Mg? 2+
2+
Mg / Mg (aq) // Zn (aq) / Zn a. b. c. d. e.
2+
! Zn
E˚ = +1.61 V
–0.85 V +0.85 V +2.37 V –2.37 V none of the above
2+
29. Given the electrochemical retivitytion shown, if the standard reduction potential of Cu 2+ standard reduction potential of Sn Sn? 2+
2+
Sn / Sn (aq) // Cu (aq) / Cu a. b. c. d. e.
is –0.76 V, what is the
! Cu
is +0.34 V, what is the
E˚ = +0.48 V
–0.14 V +0.14 V +0.37 V –0.37 V none of the above
30. Identify the strongest reducing agent based on the following half-reactions. The standard reduction potentials are listed. +1.22 V +0.61 V –0.95 V –1.48 V a. b. c.
+ – 2+ MnO2( s) + 4H (aq) + 2e ! Mn (aq) + 2H2O(l) – 2– Hg2SO4( s) + 2e ! 2Hg(l) + SO4 (aq) – – SnO2( s) + 2H2O() + 4e ! Sn( s) + 4OH (aq) – – Cr(OH)3( s) + 3e ! Cr( s) + 3OH (aq)
Cr MnO2 Hg2SO4
d. e.
Sn Hg
31. Identify the strongest oxidizing agent from the following half-reactions. The standard reduction potentials are listed. +1.22 V +0.61 V –0.95 V –1.48 V a. b. c.
+ – 2+ MnO2( s) + 4H (aq) + 2e ! Mn (aq) + 2H2O(l) – 2– Hg2SO4( s) + 2e ! 2Hg(l) + SO4 (aq) – SnO2( s) + 2H2O() + 4e ! Sn( s) + 4OH – (aq) – – Cr(OH)3( s) + 3e ! Cr( s) + 3OH (aq)
Cr MnO2 Hg2SO4
d. e.
Sn Hg
32. In one episode of the TV sitcom, Gilligan’s Island, the “professor” constructed voltaic cells to use as substitutes for their radio’s dead batteries. Which scraps of metal from their damaged boat, the Minnow , could best be used to create a 1.5 V voltaic cell? (Assume that coconuts make great beakers and that seawater is a terrific electrolyte!) Metal/Metal ion lead/lead(II) (fishing weights) iron/iron(II) (the anchor) silver/silver(I) (Mrs. Howell’s brooch) aluminum/aluminum(III) (the boat’s flagpole)
a. b. c.
silver anode and lead cathode aluminum anode and lead cathode iron anode and aluminum cathode
d. e.
E –0.126 –0.44 –0.799 –1.677
aluminum anode and silver cathode lead cathode and silver anode
7 Standard Reduction Potentials (volts) in Aqueous Solution 4+ – 2+ +1.80 Pb + 2e ! Pb 3+ – +1.50 Au + 3e ! Au 3+ – +0.771 Fe + 3e ! Fe – – +0.535 I2 + 2e ! 2 I 2+ – –0.124 Pb + 2e ! Pb 3+ – –1.66 Al + 3e ! Al 2+ – –2.37 Mg + 2e ! Mg +
–
K + e
–2.93
! K
2+
2+
33. What is the standard cell potential for a voltaic cell using the Pb /Pb and Mg /Mg half-reactions? Which metal is the cathode? (Use the Standard Reduction Potentials table shown above) a. b. c.
–2.25 V, Pb is the cathode +2.25 V, Mg is the cathode –2.25 V, Mg is the cathode
d. e.
+2.25 V, Pb is the cathode –2.49 V, Mg is the cathode
3+
3+
34. What is the standard cell potential for a voltaic cell using the Al /Al and Fe /Fe half-reactions? Which metal is the anode? (Use the Standard Reduction Potentials table shown above) a. b. c.
–2.43 V, Al is the anode +2.43 V, Al is the anode –0.89 V, Fe is the anode
d. e.
+0.89 V, Fe is the anode None of the above
35. Using the Table of Standard Reduction Potentials table shown above, which is the strongest oxidizing agent? a. b. c.
4+
Pb 2+ Pb + K
d. e.
K Al
36. Using the Table of Standard Reduction Potentials table shown above, which is the strongest reducing agent? a. b. c.
Pb4+ Pb2+ + K
d. e.
K Al
37. Use the Table of Standard Reduction Potentials table, which species would react with Fe? a. b. c.
+
Pb only + Au only + I2 and Pb
d. e.
+
Both Pb and Au + Both Pb and Au
+
38. Use the Table of Standard Reduction Potentials table, which species would react with Al 3+? a. b. c.
Pb only + Au only Fe and Pb
d. e.
+
+
Both Mg and K Both Mg and K
39. Using the Table of Standard Reduction Potentials table shown above, what is the standard cell potential for an electrochemical cell that has iron (Fe) and magnesium (Mg) electrodes? Also, identify the cathode. a. b. c.
+3.14 V with Fe as the cathode +3.14 V with Mg as the cathode –3.14 V with Fe as the cathode
d. e.
–3.14 V with Mg as the cathode +1.60 V with Fe as the cathode
8 Predictable Patterns in Oxidation and Reduction Strength. (Should be able to recognize from periodic table, but without looking at a table with reduction potentials) 40. Glancing at a periodic table, where do you expect to find elements that are good oxidizing agents? a. b. c.
on the right (except for the noble gases) in the middle left in the top left
d. e.
at the bottom in the transition metals
41. Glancing at a periodic table, where do you expect to find elements that are good reducing agents? a. b. c.
in groups 16 and 17 on the left in the middle
d. e.
at the bottom in group 17
42. Based on the periodic table and general patterns of activity, which is the correct ranking of the halogens as oxidizing agents? (you should be able to answer without looking at a reduction-potential table.) F2 a. b. c. d.
F2 (strongest oxidant) > Cl2 I2 (strongest oxidant) > Br 2 Cl2 (strongest oxidant) > F2 Br 2 (strongest oxidant) > I2
> > > >
Br 2 Cl2 Br 2 Cl2
> > > >
I2 F2 I2 F2
Cl2
Br 2
I2
(weakest oxidant) (weakest oxidant) (weakest oxidant) (weakest oxidant)
43. Based on the periodic table and general patterns of activity, which is the correct ranking of the following metals as reducing agents? (Atomic numbers shown) Mg (12) a. b. c. d.
K (19)
Au (79)
Fe (26)
Mg (strongest reducing agent) > K > Fe > Au (weakest reducing agent) K (strongest reducing agent) > Mg > Fe > Au (weakest reducing agent) Au (strongest reducing agent) > Mg > Fe > K (weakest reducing agent) Fe (strongest reducing agent) > Au > Mg > K (weakest reducing agent)
44. Based on the periodic table and general patterns of activity, which of the following would react with metallic calcium? KBr NaI FeCl2 NiBr 2 a. b. c. d.
KBr and NaI only FeCl2 only NiBr 2 only both FeCl2 and NiBr 2
45. Based on the periodic table and general patterns of activity, which of the following would react with metallic sodium? I2 I FeCl2 NiBr 2 a. b. c. d.
I2 only I only NiBr 2 only I2, FeCl2 and NiBr 2
9 Ranking Relative Activity, Based on Observed Reactivity or Lack Thereof 46. Given the following laboratory observation, which of the following statements is NOT TRUE? Sn + 2AgBr ! 2Ag + SnBr 2 2Ag + SnBr 2 ! No Reaction a. b. c. d. e.
Sn is a stronger reducing agent than Ag + 2+ Ag is a stronger oxidizing agent than Sn + 2+ The reduction potential for Ag is more positive than the reduction potential for Sn 2+ + Sn is a stronger oxidizing agent than Ag none of the above
47. Given the following laboratory observation, which of the following statements is NOT TRUE? Zn + CuBr 2 ! Cu + ZnBr 2 Cu + ZnBr 2! No Reaction a. b. c. d. e.
Zn is a stronger reducing agent than Cu +2 2+ Cu is a stronger oxidizing agent than Zn Cu is a stronger reducing agent than Zn The fact that copper doesn’t react with ZnBr 2 proves that copper loves/attracts/holds electrons more than does zinc. none of the above
48. Given the following laboratory observation, which of the following statements is NOT TRUE? Mg + NiBr 2 ! Ni + MgBr 2 Ni + MgBr 2! No Reaction 2+
a. Ni loves electrons more than Mg. That’s why Mg gives electrons to Ni 2+ b. Mg loves electrons less than Ni. That’s why Mg doesn’t take electrons from Mg c. When a redox reaction does NOT occur (equation 2), it means that the reduced form of nickel is a weaker reducing agent than the reduced form of Mg d. When a redox reaction DOES occur (equation 1), it means that the reduced form of Mg is a stronger reducing agent than the reduced form of Ni e. When a redox reaction does NOT occur (equation 2), it means that the reduced form of nickel is a stronger reducing agent than the reduced form of Mg 49. Which of the following correctly ranks the “activity” (strength as reducing agents) of the elements Ag, Au, and Sn, given the following observed reactivity information? Sn + 2AgBr ! SnBr 2 + 2Ag 3Sn + 2AuBr 3 ! 3SnBr 2 + 2Au 3Ag + AuBr 3 ! 3AgBr + Au a. b. c. d.
Sn > Ag > Au Sn > Au > Ag Au > Ag > Sn Ag > Au > Sn
50. Which of the following correctly ranks the “activity” (strength as reducing agents) of the elements Cu, Cd, and Zn, given the following observed reactivity information? Zn + CuBr 2 ! Cu + ZnBr 2 Cd + ZnBr 2 ! No Reaction Cu + CdBr 2 ! No Reaction a. b. c. d.
Zn > Cu > Cd Zn > Cd > Cu Cd > Cu > Zn Cu > Cd > Zn
10 Free Energy and Equilibrium. Key Equation:
! G˚
= –96.5nE˚cell (! G˚ in kJ/mol)
51. Given the electrochemical reaction shown, what is the standard free energy change 2+
2+
Mg / Mg (aq) // Zn (aq) / Zn a. b. c. d. e.
"G °
if E˚ = +1.61 V?
E˚ = +1.61 V
-311 kJ/mol +311 kJ/mol -155 kJ/mol +155 kJ/mol none of the above
52. The oxidation of hydrogen by oxygen is one of the most-used reactions in fuel-cell technology. The overall reaction, which is given below, has a "G° value of –474 kJ/mol. What is the standard cell potential for this fuel cell? 2H2( g ) + O2( g ) ! 2H2O(l)
a. b. c.
2.46 V 4.91 V 1.23 V
d. e.
" G°
= –474 kJ/mol
2.46 V 1.50 V
53. What is "G° for the following balanced reaction, if E˚ = +2.431 V? 3+ 3+ Al( s) + Fe (aq) ! Al (aq) + Fe( s)
a. b. c. d. e.
-704 kJ/mol +704 kJ/mol -235 kJ/mol -469 kJ/mol none of the above
54. The oxidation of methanol, as described by the equation below, has a cell potential for a methanol fuel cell? 2CH3OH + 3O2 ! 2 CO2 + 4H2O a. b. c.
E˚ = +2.431 V
0.405 V 9.72 V 0.810 V
d. e.
"G °
value of –937.9 kJ/mol. What is the standard
"G °
= –937.9 kJ/mol
–2.43 V –9.72 V
55. For the following reaction, all of the reactants and products are in their standard states/standard 1.0M concentrations. Which of the following statements must be true? Zn (s) + SnBr 2 (aq)
!
a. The reaction would be product-favored as written b. !G˚ for the reaction as written is positive c. Zinc is undergoing reduction d. none of the above
ZnBr 2 (aq) + Sn (s)
E˚ = +0.60 V
11 K Values and Voltage Key Equation: log K = nE˚/0.0592 56. When a voltaic cell reaches equilibrium, __________ a. E = 0 b. E cell = 0 c. E cell = K
d. E = K e. E cell = Q
57. Electrochemical cell potentials can be used to determine equilibrium constants that would be otherwise difficult to for the following balanced reaction, if E˚ = +0.0218 V? determine because concentrations are small. What is 3+ +2 3Zn( s) + 2Cr (aq) ! 3Zn (aq) + Cr( s)
a. b. c. d.
1.3 x 10 2.2 162 0.37
E˚ = +0.0218 V
-3
10
58. What is E˚ for the following balanced reaction, if K=4.38 x 10 ? 2+ +2 Zn( s) + Fe (aq) ! Zn (aq) + Fe( s)
a. b. c. d.
10
K= 4.38 x 10
-0.578 V +0.866 V -0.315 V +0.315 V
Nonstandard Concentrations and Cell Potential. Key Equation: Ecell = E˚ – [0.0592/n]log Q
2+
59. The value of E˚ for the following reaction is 1.10 V. What is the value of Ecell when the concentration of Cu is 1.0 M and the concentration of Zn 2+ is 0.025 M? 2+
2+
Zn(s) + Cu (aq) ! Cu (s) + Zn (aq) 1.0 M 0.025 M a. b. c. d.
E˚ = 1.10 V
1.40 V 0.95 V 1.15 V 0.80 V
60. The value of E˚ for the following reaction is 1.260 V. What is the value of Ecell given the concentrations shown? 2+
3+
2Al(s) + 3Cd (aq) ! 3Cd (s) + 2Al (aq) 0.1 M 0.6 M a. b. c. d.
E˚ = 1.260 V
1.235 V 1.285 V 1.15 V 1.37 V
61. The value of E˚ for the following reaction is 0.189 V. What is the value of Ecell given the concentrations shown? 4H+ (aq) + Fe( s) + NO3-(aq) ! Fe3+(aq) + NO(aq) + 2H2O(l) 0.1 M a. b. c. d.
-0.215 V 0.112 V 0.189 V 0.266 V
0.6 M
1.0 M
0.5 M
E˚ = 0.189 V
12 Electrolysis: Key Equations: Mol e – = [A • time (sec)/96,500]
time (sec)= mol e • 96,500/current (in A)
62. Copper metal (63.546 g/mol) is purified by electrolysis. How much copper metal (in grams) could be produced from copper(II) oxide by applying a current of 10.0 amps at the appropriate negative potential for 12.0 hours? a. b. c.
284 g 142 g 28.4 g
d. e.
14.2 g 4.48 g
63. How long would it take to electroplate a flute with 28.3 g of silver (107.87 g/mol) at a constant current of 2.0 amps using AgNO3? a. b. c.
211 min 422 min 844 min
d. e.
1688 min 105 min
64. How many grams of aluminum metal (26.982 g/mol) can be produced by the electrolysis of Al 2O3 using a current of 100 amperes for 24 hours? a. b. c.
805 2,400 8.1 x 10
d. e.
13
2.2 $ 10 12 7.5 $ 10
65. If in using a lead-acid battery to start a car, 1.00 gram of Pb (207.2 g/mol) is consumed on the anode , how long will it take to recharge the battery, using a current of 0.500 amperes to turn the PbSO 4 that was produced back into Pb? a. b. c.
15.5 min 1864 min 31 min
d. e.
21 min 42 min
66. Chromium often is electroplated on other metals and even plastics to produce a shiny metallic appearance. How many grams of chromium (51.996 g/mol) would plate out from a solution of Cr(NO3)3 when 10 amps of current are passed through the electrolytic cell for 5.36 hours? a. b. c.
17.3 g 34.7 g 52.0 g
d. e.
104 g 11.6 g
67. Suppose an aluminum (26.982 g/mol) beer can weighs 40.0 g. For how long would a current of 100.0 amp need to be passed through a molten AlF 3 electrolysis cell to produce enough aluminum to replace a discarded beer can? a. b. c.
4.44 hr 23.8 min 1.19 hr
d. e.
42.7 min 2.38 hr
13 General Chemistry II Jasperse Electrochemistry. Extra Practice Problems 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34.
D B A C B B D A D B B D A B E C E D C B A A A C A C D D A A B B D B
ANSWERS
35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. 47. 48. 49. 50. 51. 52. 53. 54. 55. 56. 57. 58. 59. 60. 61. 62. 63. 64. 65. 66. 67.
A D D E A A B A B D D D C E A B A C A C A B C (162) D C A B B A A C B C