Unit 6 Electrochemistry

6.3 Exercises

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Section 6.3 Exercises

  1. Write the following balanced reactions using cell notation. Use platinum as an inert electrode, if needed.

    (a) [latex]\text{Mg}(s)\;+\;\text{Ni}^{2+}(aq)\;{\longrightarrow}\;\text{Mg}^{2+}(aq)\;+\;\text{Ni}(s)[/latex]

    (b) [latex]2\text{Ag}^{+}(aq)\;+\;\text{Cu}(s)\;{\longrightarrow}\;\text{Cu}^{2+}(aq)\;+\;2\text{Ag}(s)[/latex]

    (c) [latex]\text{Mn}(s)\;+\;\text{Sn(NO}_3)_2(aq)\;{\longrightarrow}\;\text{Mn(NO}_3)_2(aq)\;+\;\text{Au}(s)[/latex]

    (d) [latex]3\text{CuNO}_3(aq)\;+\;\text{Au(NO}_3)_3(aq)\;{\longrightarrow}\;3\text{Cu(NO}_3)_2(aq)\;+\;\text{Au}(s)[/latex]

  2. Given the following cell notations, write the corresponding balanced reactions.

    (a) [latex]\text{Mg}(s){\mid}\text{Mg}^{2+}(aq){\parallel}\text{Cu}^{2+}(aq){\mid}\text{Cu}(s)[/latex]

    (b) [latex]\text{Ni}(s){\mid}\text{Ni}^{2+}(aq){\parallel}\text{Ag}^{+}(aq){\mid}\text{Ag}(s)[/latex]

  3. Identify the species oxidized, species reduced, and the oxidizing agent and reducing agent for all the following reactions.
    (a) [latex]\text{Al}(s)\;+\;\text{Zr}^{4+}(aq)\;{\longrightarrow}\;\text{Al}^{3+}(aq)\;+\;\text{Zr}(s)[/latex]

    (b) [latex]\text{Ag}^{+}(aq)\;+\;\text{NO}(g)\;{\longrightarrow}\;\text{Ag}(s)\;+\;\text{NO}_3^{\;\;-}(aq)\;\;\;\;\;\;\;\text{(acidic solution)}[/latex]

    (c) [latex]\text{SiO}_3^{\;\;2-}(aq)\;+\;\text{Mg}(s)\;{\longrightarrow}\;\text{Si}(s)\;+\;\text{Mg(OH)}_2(s)\;\;\;\;\;\;\;\text{(basic solution)}[/latex]

    (d) [latex]\text{ClO}_3^{\;\;-}(aq)\;+\;\text{MnO}_2(s)\;{\longrightarrow}\;\text{Cl}^{\;\;-}(aq)\;+\;\text{MnO}_4^{\;\;-}(aq)\;\;\;\;\;\;\;\text{(basic solution)}[/latex]

  4. Why is a salt bridge necessary in galvanic cells?
  5. (a) An active (metal) electrode was found to lose mass as the oxidation-reduction reaction was allowed to proceed. Was the electrode part of the anode or cathode? Explain.
    (b) An active (metal) electrode was found to gain mass as the oxidation-reduction reaction was allowed to proceed. Was the electrode part of the anode or cathode? Explain.
  6. For each reaction listed, determine its standard cell potential at 25 °C.

    (a) [latex]\text{Mg}(s)\;+\;\text{Ni}^{2+}(aq)\;{\longrightarrow}\;\text{Mg}^{2+}(aq)\;+\;\text{Ni}(s)[/latex]

    (b) [latex]2\text{Ag}^{+}(aq)\;+\;\text{Cu}(s)\;{\longrightarrow}\;\text{Cu}^{2+}(aq)\;+\;2\text{Ag}(s)[/latex]

    (c) [latex]\text{Mn}(s)\;+\;\text{Sn(NO}_3)_2(aq)\;{\longrightarrow}\;\text{Mn(NO}_3)_2(aq)\;+\;\text{Sn}(s)[/latex]

    (d) [latex]3\text{Fe(NO}_3)_2(aq)\;+\;\text{Au(NO}_3)_3(aq)\;{\longrightarrow}\;3\text{Fe(NO}_3)_3(aq)\;+\;\text{Au}(s)[/latex]

  7. (a) Determine the standard cell potential at 25 °C for the reaction involving the galvanic cell in which cadmium metal is oxidized to 1 M cadmium(II) ion and a half-cell consisting of an aluminum electrode in 1 M aluminum nitrate solution.
    (b) Can the reaction in part (a) be carried out in an electrolytic cell under the given conditions?
  8. Determine the standard cell potential at 25 °C for this reaction.
    [latex]\text{Cu}(s){\mid}\text{Cu}^{2+}(aq){\parallel}\text{Au}^{3+}(aq){\mid}\text{Au}(s)[/latex]

Solutions

  1. (a) [latex]\text{Mg}(s){\mid}\text{Mg}^{2+}(aq){\parallel}\text{Ni}^{2+}(aq){\mid}\text{Ni}(s)[/latex]; (b) [latex]\text{Cu}(s){\mid}\text{Cu}^{2+}(aq){\parallel}\text{Ag}^{+}(aq){\mid}\text{Ag}(s)[/latex]; (c) [latex]\text{Mn}(s){\mid}\text{Mn}^{2+}(aq){\parallel}\text{Sn}^{2+}(aq){\mid}\text{Sn}(s)[/latex]; (d) [latex]\text{Pt}(s){\mid}\text{Cu}^{+}(aq)\text{, Cu}^{2+}(aq){\parallel}\text{Au}^{3+}(aq){\mid}\text{Au}(s)[/latex]
  2. (a) [latex]\text{Mg}(s)\;+\;\text{Cu}^{2+}(aq)\;{\longrightarrow}\;\text{Mg}^{2+}(aq)\;+\;\text{Cu}(s)[/latex]; (b) [latex]2\text{Ag}^{+}(aq)\;+\;\text{Ni}(s)\;{\longrightarrow}\;\text{Ni}^{2+}(aq)\;+\;2\text{Ag}(s)[/latex]
  3. Species oxidized = reducing agent: (a) Al(s); (b) NO(g); (c) Mg(s); and (d) MnO2(s); Species reduced = oxidizing agent: (a) Zr4+(aq); (b) Ag+(aq); (c) SiO32−(aq); and (d) ClO3−(aq)
  4. Without the salt bridge, the circuit would be open (or broken) and no current could flow. With a salt bridge, each half-cell remains electrically neutral and current can flow through the circuit.
  5. (a) Active electrodes participate in the oxidation-reduction reaction. Since metals form cations, the electrode would lose mass if metal atoms in the electrode were to oxidize and go into solution. Oxidation occurs at the anode.
    (b) Because the electrode gained mass, the metal cations in solution was reduced to metal on the cathode.
  6. (a) +2.12 V; (b) +0.463 V; (c) +1.059 V; (d) +0.727 V
  7. (a) −1.259 V
    (b) It seems possible if we supplied more than 1.259 V. However, the solvent, H2O, is a stronger oxidizing agent than Al3+ and thus, H2O will be reduced instead at the cathode.
  8. +1.161 V

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