Question

Which balanced redox reaction is occurring in the voltaic cell represented by the notation of \(\mathrm{Al}(\mathrm{s})\left|\mathrm{Al}^{3+}(\mathrm{aq}) \| \mathrm{Pb}^{2+}(\mathrm{aq})\right| \mathrm{Pb}(\mathrm{s}) ?\)

Select one:

Q \(\mathrm{Al}(\mathrm{s})+\mathrm{Pb}^{2+}(\mathrm{aq}) \longrightarrow \mathrm{Al}^{3+}(\mathrm{aq})+\mathrm{Pb}(\mathrm{s})\)

\bigcirc \(2 \mathrm{Al}^{3+}(\mathrm{aq})+3 \mathrm{~Pb}(\mathrm{~s}) \longrightarrow 2 \mathrm{Al}(\mathrm{s})+3 \mathrm{~Pb}^{2+}\) (aq)

Q \(\mathrm{Al}^{3+}(\mathrm{aq})+\mathrm{Pb}(\mathrm{s}) \longrightarrow \mathrm{Al}(\mathrm{s})+\mathrm{Pb}^{2+}(\mathrm{aq})\)

\(2 \mathrm{Al}(\mathrm{s})+3 \mathrm{~Pb}^{2+}(\mathrm{aq}) \longrightarrow 2 \mathrm{Al}^{3+}(\mathrm{aq})+3 \mathrm{~Pb}(\mathrm{~s})\)

Answer 1

Given cell notation is, \(\mathrm{Al}(\mathrm{s})\left|\mathrm{Al}^{3+}(\mathrm{aq}) \| \mathrm{Pb}^{2+}(\mathrm{aq})\right| \mathrm{Pb}(\mathrm{s})\)

In this notation, \(\|\) represents salt bridge. The half-cell present on the left side of salt bridge represents oxidation half reaction. The half-cell present on the right side of salt bridge represents reduction half reaction. Oxidation half reaction: \(\mathrm{Al}(\mathrm{s}) \longrightarrow \mathrm{Al}^{3+}(a q)+3 \mathrm{e}^{-}\)

Reduction half reaction \(: \mathrm{Pb}^{2+}(\mathrm{aq})+2 \mathrm{e}^{-} \longrightarrow \mathrm{Pb}(\mathrm{s})\)

The number of electrons lost is not equal to number of electrons gained. Thus, to get balanced redox reaction multiply the oxidation half reaction with 2 and the reduction reaction with 3 . Add the resultant reactions.

\(2 \mathrm{Al}(\mathrm{s}) \longrightarrow 2 \mathrm{Al}^{3+}(\mathrm{aq})+6 \mathrm{e}^{-}\)

\(3 \mathrm{~Pb}^{2+}(\mathrm{aq})+6 \mathrm{e}^{-} \longrightarrow 3 \mathrm{~Pb}(\mathrm{~s})\)

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\(2 \mathrm{Al}(\mathrm{s})+3 \mathrm{~Pb}^{2+}(\mathrm{aq}) \longrightarrow 2 \mathrm{Al}^{3+}(\mathrm{aq})+3 \mathrm{~Pb}(\mathrm{~s})\)