How does electrolysis work?
Resposta curta
Electrolysis uses electricity to break down an ionic compound that is molten or dissolved, called the electrolyte. Positive ions move to the negative electrode (cathode) and gain electrons. Negative ions move to the positive electrode (anode) and lose electrons. Remember OIL RIG: oxidation is loss, reduction is gain of electrons.
Passo a passo
- Melt or dissolve the ionic compound so the ions can move.
- Pass a direct current through it using two inert electrodes.
- Cations (positive) are attracted to the cathode and are reduced.
- Anions (negative) are attracted to the anode and are oxidised.
- In aqueous solutions, water also provides H⁺ and OH⁻ ions, which can be discharged instead.
Exemplo resolvido
Electrolysis of molten lead bromide, PbBr₂
- Cathode: Pb²⁺ + 2e⁻ gives Pb (lead metal forms)
- Anode: 2Br⁻ gives Br₂ + 2e⁻ (brown bromine gas)
- The compound must be molten so the ions are free to move
Erros comuns
- Saying electrons flow through the electrolyte. Ions carry the charge in the electrolyte.
- Mixing up anode and cathode. PANIC: positive anode, negative is cathode.
- Forgetting the rule for aqueous solutions: hydrogen forms at the cathode if the metal is more reactive than hydrogen.
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