Question

What is the cathode in mg(s) | mg2+(aq) || au+(aq) | au(s) mg2+ + 2 e − → mg e ◦ red = −2.36 au+ + e − → au e ◦ red = +1.69 and what is the cell type? 1. mg(s); an elec?

Answer 1

Cathode:
`\text{Au} \; (s)`

A Voltaic Cell

Step-by-step explanation

Reduction occurs at the cathode in both electrochemical cells and voltaic cells. The species that gains electrons in a redox process is being reduced. Recall that
`\Delta G = - n F E`; the species with the most positive standard cell potential would have the reduction reaction with the most negative change in Gibbs free energy and is therefore most stable when reduced than in the original state. The reduction potential of
`\text{Au}^(+)` is higher than that of
`\text{Mg}^(2+)`; as a result,
`\text{Au}^(+)` would readily gain electrons from the
`\text{Mg} \; (s)` electrode to produce
`\text{Au} \; (s)` when connected with an external circuit. Therefore the
`\text{Au}` electrode, immersed in the
`\text{Au}^(+)` solution which experiences reduction, would serve as the cathode.

The reaction one would expect to observe in this cell

`\text{Mg} \; (s) + 2 \; \text{Au}^(+) \; (aq) \to \text{Mg}^(2+) \; (aq) + 2 \; \text{Au} \; (s)`

has a standard cell potential
`\Delta E ^{\text{o}}` of
`+4.05 \; \text{V} > 0 \; \text{V}`. The overall reaction is exothermic and leads to the release of energy. The cell is therefore a voltaic cell.