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Chapter 17: Q47E (page 961)
Why would a sacrificial anode made of lithium metal be a bad choice despite its \({\bf{E}}_{{\bf{Li}}}^{\bf{^\circ }}{\bf{ + Li = - 3}}{\bf{.04\;V}}\), which appears to be able to protect all the other metals listed in the standard reduction potential table?
Lithium is a very reactive metal.
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Aluminium\(\left( {{\bf{E}}_{{\bf{A}}{{\bf{l}}^{{\bf{3 + }}}}{\bf{/Al}}}^{\bf{^\circ }}{\bf{ = - 2}}{\bf{.07\;V}}} \right)\) is more easily oxidized than iron \(\left( {{\bf{E}}_{{\bf{F}}{{\bf{e}}^{\bf{3}}}}^{\bf{^\circ }}{\bf{/F}}{{\bf{e}}^{\bf{ - }}}{\bf{ = - 0}}{\bf{.477\;V}}} \right){\bf{,}}\) and yet when both are exposed to the environment, untreated aluminium has very good corrosion resistance while the corrosion resistance of untreated iron is poor. Explain this observation.
Identify the species that undergoes oxidation, the species that undergoes reduction, the oxidizing agent, and thereducing agent in each of the reactions of the previous problem.
\(\begin{array}{l}{\bf{(a) H_2O_2 + S}}{{\bf{n}}^{{\bf{2 + }}}} \to {\bf{H_2O + S}}{{\bf{n}}^{{\bf{4 + }}}}\\{\bf{(b) PbO_2 + Hg}} \to {\bf{Hg}}{{\bf{2}}^{{\bf{2 + }}}}{\bf{ + P}}{{\bf{b}}^{{\bf{2 + }}}}\\{\bf{(c) Al + Cr_2O}}{{\bf{7}}^{{\bf{2 - }}}} \to {\bf{A}}{{\bf{l}}^{{\bf{3 + }}}}{\bf{ + C}}{{\bf{r}}^{{\bf{3 + }}}}\end{array}\)
Given the following cell notations, determine the species oxidized, species reduced, and the oxidizing agent and reducing agent, without writing the balanced reactions
a. \({\rm{Mg}}(s)\left| {{\rm{M}}{{\rm{g}}^{2 + }}(aq) || {\rm{C}}{{\rm{u}}^{2 + }}(aq)} \right|{\rm{Cu}}(s)\)
b.\({\rm{Ni}}(s)\left| {{\rm{N}}{{\rm{i}}^{2 + }}(aq) || {\rm{A}}{{\rm{g}}^ + }(aq)} \right|{\rm{Ag}}(s)\)
For each of the following balanced half-reactions, determine whether an oxidation or reduction is occurring.
(a) \({\bf{F}}{{\bf{e}}^{{\bf{3 + }}}}{\bf{ + 3}}{{\bf{e}}^{\bf{ - }}} \to {\bf{Fe}}\)
(b) \({\bf{Cr}} \to {\bf{C}}{{\bf{r}}^{{\bf{3 + }}}}{\bf{ + 3}}{{\bf{e}}^{\bf{ - }}}\)
(c) \({\bf{MnO}}_{\bf{4}}^{{\bf{2 - }}} \to {\bf{MnO}}_{\bf{4}}^{\bf{ - }}{\bf{ + }}{{\bf{e}}^{\bf{ - }}}\)
(d) \({\bf{L}}{{\bf{i}}^{\bf{ + }}}{\bf{ + }}{{\bf{e}}^{\bf{ - }}} \to {\bf{Li}}\)
For the standard cell potentials given here, determine the \(\Delta {G\circ }\) for the cell in \({\rm{kJ}}\).
(a) \(0.000\;{\rm{V}},{\rm{n}} = 2\)
(b) \( + 0.434\;{\rm{V}},{\rm{n}} = 2\)
(c) \( - 2.439\;{\rm{V}},{\rm{n}} = 1\)
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