4.2 Standard potentials

Table of standard electrode potentials

1. In your own words, explain what is meant by the 'electrode potential' of a metal.
2. Give the standard electrode potential for each of the following metals:
   1. magnesium
   2. lead
   3. nickel
3. Refer to the electrode potentials in [link] .
   1. Which of the metals is most likely to be oxidised?
   2. Which metal is most likely to be reduced?
   3. Which metal is the strongest reducing agent?
   4. In the copper half-reaction, does the equilibrium position for the reaction lie to the left or to the right? Explain your answer.
   5. In the mercury half-reaction, does the equilibrium position for the reaction lie to the left or to the right? Explain your answer.
   6. If silver was added to a solution of copper sulphate, would it displace the copper from the copper sulphate solution? Explain your answer.
4. Use the table of standard electrode potentials to put the following in order from the strongest oxidising agent to the weakest oxidising agent .
   • Cu ${}^{2+}$
   • MnO ${}_4^{-}$
   • Br ${}_2$
   • Zn ${}^{2+}$
5. Look at the following half-reactions.
   • $C{a}^{2+}+2e^{-}\to Ca$
   • $C{l}_2+2e^{-}\to 2Cl$
   • $F{e}^{3+}+3e^{-}\to Fe$
   • $I_2+2e^{-}\to 2I^{-}$
   1. Which substance is the strongest oxidising agent?
   2. Which substance is the strongest reducing agent?
6. Which one of the substances listed below acts as the oxidising agent in the following reaction? $3{\mathrm{SO}}_2+{\mathrm{Cr}}_2{\mathrm{O}}_7^{2-}+2{\mathrm{H}}^{+}\to 3{\mathrm{SO}}_4^{2-}+2{\mathrm{Cr}}^{3+}+{\mathrm{H}}_2\mathrm{O}$
   1. H ${}^{+}$
   2. Cr ${}^{3+}$
   3. SO ${}_2$
   4. Cr ${}_2$ O ${}_7^{2-}$
   (IEB Paper 2, 2004)
7. If zinc is added to a solution of magnesium sulphate, will the zinc displace the magnesium from the solution? Give a detailed explanation for your answer.

Combining half cells

Let's stay with the example of the zinc and copper half cells. If we combine these cells as we did earlier in the chapter ( "The Galvanic Cell" ), the following two equilibria exist: