Chemistry: Molecular Nature of Matter and Change, 6th Edition (Silberberg)

Chapter 21: Electrochemistry: Chemical Change and Electrical Work

Self-Assessment Quiz 2

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1
Balance the following redox equation occurring in aqueous solution:
KMnO4 + KCl + H2SO4 → MnSO4 + K2SO4 + H2O + Cl2
What is the stoichiometric coefficient for chlorine (Cl2) when the equation is balanced with smallest whole number coefficients?
A)1
B)3
C)5
D)8
E)10
2

In the shorthand notation for an electrochemical cell, what does a single vertical line (|) represent?

A)the cathode
B)the anode
C)a salt bridge
D)a phase boundary
E)the external wire connecting anode to cathode
3
A voltaic cell is based on the following two half-reactions:
Ni+2(aq) + 2e- → Ni(s) E° = -0.25 V
Cr+3(aq) + 3e- → Cr(s) E° = -0.74 V
Sketch the cell and then select the correct statement about it.
A)Cr serves as the cathode.
B)The direction of electron flow through the external wire is from the Ni to the Cr electrode.
C)Anions in solution will migrate toward the Ni+2/Ni electrode.
D)The net cell reaction is 3Ni+2(aq) + 2Cr(s) → 3Ni(s) + 2Cr+3(aq)
E)
<a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=gif::::/sites/dl/free/0310402656/38224/Image26.gif','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (0.0K)</a> = 0.99 V
4
Consider the following electrochemical cell reaction:
2Fe2+(aq) + Cu2+(aq) → 2Fe3+(aq) + Cu(s)
Use the table of standard electrode potentials in your textbook to calculate the standard cell potential for the above reaction.
A)-0.43 V
B)+0.43 V
C)+0.78 V
D)-0.78 V
E)+1.11 V
5
Consider the following two electrode reactions and their standard electrode potentials:
Al+3(aq) + 3e- → Al(s) E° = -1.66 V
Cd+2(aq) + 2e- → Cd(s) E° = -0.40 V
Write the cell reaction for a voltaic cell based on these two electrodes, and calculate the standard cell potential, <a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=gif::::/sites/dl/free/0310402656/37547/Image26.gif','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (5.0K)</a>.
A)2Al+3(aq) + 3Cd+2(aq) → 2Al(s) + 3Cd(s) <a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=gif::::/sites/dl/free/0310402656/37547/Image26.gif','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (0.0K)</a> = 2.10 V
B)2Al(s) + 3Cd+2(aq) → 2Al+3(aq) + 3Cd(s) <a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=gif::::/sites/dl/free/0310402656/37547/Image26.gif','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (0.0K)</a> = 1.26 V
C)2Al(s) + 3Cd+2(aq) → 2Al+3(aq) + 3Cd(s) <a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=gif::::/sites/dl/free/0310402656/37547/Image26.gif','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (0.0K)</a> = 3.78V
D)2Al+3(aq) + 3Cd(s) → 2Al(s) + 3Cd+2(aq) <a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=gif::::/sites/dl/free/0310402656/37547/Image26.gif','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (0.0K)</a> = 1.26 V
E)2Al+3(aq) + 3Cd(s) → 2Al(s) + 3Cd+2(aq) <a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=gif::::/sites/dl/free/0310402656/37547/Image26.gif','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (0.0K)</a> = 2.10 V
6
Consider the following standard reduction potentials, E°, in acid solution:
Al3+(aq) + 3e- → Al(s) E° = -1.66 V
Sn4+(aq) + 2e- → Sn2+(aq) E° = +0.14 V
I2(s) + 2e- → 2I-(aq) E° = +0.53 V
Under standard conditions, which of the following species is the most likely to gain electrons in a reaction?
A)Al3+(aq)
B)Al(s)
C)I-(aq)
D)I2 (s)
E)Sn4+(aq)
7

Consult the table of standard electrode potentials in your textbook in order to decide which one of the following reagents is capable of reducing I2(s) to I-(aq, 1 M).

A)Br-(aq)
B)Ag(s)
C)Sn(s)
D)Zn2+(aq, 1 M)
E)Sn4+(aq,1 M)
8
A redox reaction which involves the transfer of 3 electrons has an equilibrium constant Kc of
1.8 ´ 1017. What is the standard cell potential at 25°C of a voltaic cell based on this reaction?
(F = 96500 C/mol)
A)-1.20 V
B)-0.68 V
C)+0.12 V
D)+0.34 V
E)+1.20 V
9
A voltaic cell consists of Mn/Mn2+ and Cd/Cd2+ half-cells with concentrations [Mn2+] = 0.75 M and [Cd2+] = 0.15 M. Use the Nernst equation to calculate the cell potential, Ecell, at 25° C.
(F = 96500 C/mol)
Data: Cd+2(aq) + 2e- → Cd(s) E° = -0.40 V
Mn+2(aq) + 2e- → Mn(s) E° = -1.18 V
A)1.60 V
B)1.56 V
C)1.54 V
D)0.80 V
E)0.76 V
10
Consider the following cell reaction and its standard cell potential:
2Cr(s) + 3Pb2+(aq) → 3Pb(s) + 2Cr3+(aq) <a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=gif::::/sites/dl/free/0310402656/37547/Image26.gif','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (0.0K)</a> = 0.61 V
Calculate the equilibrium constant Kc for this reaction at 25°C. (F = 96500 C/mol)
A)4 ´ 1020
B)8 ´ 1030
C)9 ´ 1045
D)3 ´ 1051
E)8 ´ 1061
11
Which of the following types of electrochemical cell is most likely to find use in the future as a power source for electric vehicles?
A)fuel cell
B)nickel-metal hydride cell
C)dry cell
D)alkaline battery
E)lithium-ion battery
12
Select the incorrect statement relating to the corrosion of iron in air.
A)Fe2+ is formed in the anodic region.
B)O2 is oxidized in the cathodic region.
C)Electrons travel through the iron metal between the anodic and cathodic regions.
D)Moisture provides a pathway for ions to migrate.
E)Rust is a hydrated form of iron(III) oxide.
13
Use the following standard electrode potentials to predict the species formed at the electrodes in the electrolysis of aqueous CuSO4.
O2(g) + 4H+(aq) + 4e- → 2H2O(l) E° = +1.23 V
Cu2+(aq) + 2e- → Cu(s) E° = +0.34 V
SO42-(aq) + 4H+(aq) + 2e- → H2SO3(aq) + H2O(l) E° = 0.20 V
2H+(aq) + 2e- → H2(g) E° = 0.00 V
A)H2, O2, H+
B)Cu, O2, H+
C)Cu, H2
D)H2, H2SO3, H2O
E)H2SO3, H2O, O2, H+
14

In an electrolytic cell, a current of 3.00 A is passed through an aqueous solution of sodium chloride for a period of 5.00 min. What volume of chlorine gas (Cl2), measured at 25°C and 1.00 atm, will be formed at the anode? (F = 96500 C/mol)

A)4.61 L
B)1.24 L
C)456 mL
D)228 mL
E)114 mL
15
A constant current was passed through a solution of KAuCl4 between gold electrodes. Over a period of 20.00 min, the cathode increased in mass by 2.664 g. What was the current in amperes?
(F = 96500 C/mol)
Cathode half-reaction: AuCl4-(aq) + 3e- → Au(s) + 4Cl-(aq)
A)1.08 A
B)3.26 A
C)2.17 A
D)6.52 A
E)3.48 A
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