3.2.6—Primary (voltaic) cells

A voltaic cell uses a spontaneous redox reaction to convert chemical energy to electrical energy. Electrons flow through the wire from anode to cathode; the salt bridge carries ions to maintain charge neutrality.

Both half-cells connect to the external circuit and the salt bridge must contact both solutions.

In a Zn|Zn²⁺ || Cu²⁺|Cu cell, Zn is oxidized at the negative anode and electrons travel through the wire to the positive Cu cathode, where Cu²⁺ is reduced. Salt-bridge anions migrate toward the anode compartment and cations toward the cathode compartment to prevent charge buildup; electrons do not flow through the bridge.

Representative question

[Maximum number: 3]

Simple cells rely on differences in standard electrode potential values between different elements and their ions. The following is an incomplete diagram for measuring a cell potential between $\mathrm{Mn}^{2+}(\mathrm{aq}) / \mathrm{Mn}$ and $\mathrm{Ni}^{2+}(\mathrm{aq}) / \mathrm{Ni}$ half-cells.

Draw the missing components and fully label the diagram to show how the cell potential can be measured.

Retrieve the route: assign oxidation states, balance half-equations, predict displacement, label cells, trace electrons and ions, follow organic redox pathways, calculate potentials and choose electrolysis products.

Check electron loss/gain, anode/cathode versus polarity, spontaneous sign, salt-bridge direction, ions present, organic functional-group direction and object-cathode placement.

3.2.6—Primary (voltaic) cells

Voltaic Cells

Completing a Voltaic-Cell Diagram

Assessment in practice

Electron Transfer Reactions Summary

Question 1