Electrolysis
Using electricity to break down compounds and electroplating
Electrolysis uses electrical energy to decompose ionic compounds. Requires electrolyte (molten or dissolved ionic compound) and two electrodes.
Key rules:
- Cathode (negative electrode) — positive ions (cations) attracted here → REDUCED (gain electrons)
- Anode (positive electrode) — negative ions (anions) attracted here → OXIDISED (lose electrons)
- OIL RIG: Oxidation Is Loss, Reduction Is Gain (of electrons)
Electrolysis of brine (NaCl solution):
- Cathode: 2H⁺ + 2e⁻ → H₂ gas
- Anode: 2Cl⁻ → Cl₂ + 2e⁻
- Products: chlorine gas, hydrogen gas, sodium hydroxide solution — all industrially important
Electrolysis of copper sulfate (CuSO₄):
- Cathode: Cu²⁺ + 2e⁻ → Cu (copper deposited)
- Anode: Cu → Cu²⁺ + 2e⁻ (copper dissolved from anode)
- Used for purifying copper and electroplating
Electroplating: Coat a cheaper metal with a more expensive/attractive one. Object to be plated = cathode. Plating metal = anode. Electrolyte = salt of the plating metal.
Key Points to Remember
- 1Cathode: cations reduced (gain electrons). Anode: anions oxidised (lose electrons)
- 2OIL RIG: Oxidation Is Loss, Reduction Is Gain
- 3Electrolysis of brine: Cl₂, H₂, NaOH produced
- 4Electroplating: object = cathode, plating metal = anode
Pakistan Example
Electroplating Jewellery in Karachi's Saddar Market
The jewellery bazaars of Karachi's Saddar area use electroplating daily — cheap brass jewellery is silver-plated for export. The brass item becomes the cathode, a silver bar becomes the anode, and silver nitrate solution is the electrolyte. Silver ions (Ag⁺) are reduced at the cathode, coating the jewellery. Chlorine from brine electrolysis at industrial sites near Karachi is used to purify water — the same EdExcel chemistry.
Quick Revision Infographic
Chemistry — Quick Revision
Electrolysis
Key Concepts
Formulas to Know
plating metal = anodeElectroplating Jewellery in Karachi's Saddar Market
The jewellery bazaars of Karachi's Saddar area use electroplating daily — cheap brass jewellery is silver-plated for export. The brass item becomes the cathode, a silver bar becomes the anode, and silver nitrate solution is the electrolyte. Silver ions (Ag⁺) are reduced at the cathode, coating the jewellery. Chlorine from brine electrolysis at industrial sites near Karachi is used to purify water — the same EdExcel chemistry.