Chemistry · 4 Electrochemistry · Paper 5/6 practical
Electrolysis. Split it apart.
Pass a direct current through molten or aqueous electrolytes and watch the products form. Cations move to the cathode (–), anions to the anode (+). Predict and observe the product at each electrode for five classic cells.
0620 Topic 4 — Electrochemistry
cathode (–) · anode (+)
Paper 5/6 — Practical
power off
at cathode —
Choose the cell
—
Products & observations
Cathode (–)
?
Anode (+)
?
Electrolyte / notes
switch on to observe…
Half-equations & tests
Select a cell to see the electrode reactions.
📋 Method & key ideas
- Cations (positive ions) are attracted to the cathode (negative electrode) where they gain electrons (reduction).
- Anions (negative ions) move to the anode (positive electrode) where they lose electrons (oxidation).
- In aqueous solutions, water also provides H⁺ and OH⁻ — the less reactive ion is usually discharged: H₂ at the cathode unless a less reactive metal (e.g. copper) is present; a halogen at the anode if its ion is concentrated, otherwise O₂.
- Test the gases: H₂ pops, O₂ relights a glowing splint, Cl₂ bleaches damp litmus.
- Use inert carbon (graphite) or platinum electrodes unless the electrode is meant to take part (electroplating, purification).
⚠ Safety & precautions
- Molten lead(II) bromide and bromine vapour are toxic — use a fume cupboard and small quantities.
- Chlorine from brine is toxic — ventilate well.
- Identify electrodes correctly: anode is connected to the + terminal.
🎯 Syllabus reference (0620)
- 4 Electrochemistry — describe electrolysis of molten PbBr₂, concentrated aqueous NaCl, dilute sulfuric acid and aqueous copper(II) sulfate (with carbon and with copper electrodes); identify products and write electrode half-equations (Supplement); electroplating.