3.2.5—Electrodes in electrochemical cells
- Syllabus
- First assessment 2025
- Objective
- 3.2.5
- Level
- SL
Anodes, Cathodes and Polarity
Oxidation always occurs at the anode and reduction always occurs at the cathode. In a voltaic cell the anode is negative and cathode positive; in an electrolytic cell the anode is positive and cathode negative.
Name electrodes from the half-reactions before assigning signs. Electrons leave the anode and reach the cathode through the external circuit; a power supply reverses the polarities in an electrolytic cell but never changes where oxidation and reduction occur.
Labelling Electrochemical Cells
Assessment in practice
Representative question
Question 1
[Maximum number: 2]
Annotate the electrolytic cell with the terms anode and cathode, and show the direction of ion movement.
Do not apply ECF.
Award 1 mark for any 2 correct of the 4
Electron Transfer Reactions Summary
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.