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A solder bath holds 0.32 mol/L tin(II) ions and 0.032 mol/L lead(II) ions…

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A solder bath holds $0.32\ \text{mol/L}$ tin(II) ions and $0.032\ \text{mol/L}$ lead(II) ions. The standard potentials are $-0.14\ \text{V}$ for $\text{Sn}^{2+}/\text{Sn}$ and $-0.13\ \text{V}$ for $\text{Pb}^{2+}/\text{Pb}$ . (a) Find the potential at which each metal starts to deposit at $298\ \text{K}$ . (b) Which goes first? (c) What ratio $[\text{Pb}^{2+}]/[\text{Sn}^{2+}]$ makes the two start together?

Need a reminder? The key ideaShow

At the cathode the ion with the highest deposition potential goes first, and at the anode the lowest goes first. $E_{dep} = E^\circ \pm \dfrac{0.0591\ \text{V}}{n}\log c$ . Hydrogen evolves at $E_H = -0.0591\ \text{V} \times \text{pH} - \eta$ . Current efficiency is the mass deposited divided by the mass expected from $m = \dfrac{Q}{zF}M$ , times 100. Energy is $VQ$ , and $1\ \text{kWh} = 3.6 \times 10^6\ \text{J}$ .

The worked solution

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