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Cathode Negative
Anode Positive
Oxidation is loss
Reduction is gain
Oxidation Anode
Reduction Cathode
Humphry Davy
- used it to extract reactive group I and group II elements
- producing reactive metals, eg Na, K, Al
- producing hydrogen and oxygen
- purifying copper
- electrolplating, silver-plating nickel cutlery
the use of electricity to bring about a chemical reaction in a electrolyte, ie a chemical reaction is produced when an electric current is passed through an electrolyte
- the rods that dip into the electrolyte and make electrical contact with it
- carbon or platinum as they are unreactive
Electrolysis of aqueous copper(II) sulphate using copper electrodes:
Anode: the solid copper electrode is oxidised
Cu - 2e⁻ → Cu²⁺
Cathode: copper ions from the copper sulphate solution are reduced
Cu²⁺ + 2e⁻ → Cu
Result: cathode increases in size as copper ions change into solid copper atoms + build up on the electrode (impurities fall to the bottom)
Electrolysis of acidified water using inert electrodes:
Anode: water is oxidised
H₂O - 2e⁻ → 2H⁺ + ½O₂
Cathode: hydrogen ions are reduced
2H⁺ + 2e⁻ → H₂
Result: twice as much gas is collected at the cathode
Electrolysis of aqueous sodium sulphate solution using universal indicator and inert electrodes:
Anode: water oxidised (since the SO₄²⁻ ions are too stable to be discharged)
H₂O - 2e⁻ → 2H⁺ + ½O₂
Cathode: water molecules are reduced (since the Na⁺ ion are too stable to be discharged)
2H₂O + 2e⁻ → H₂ +2OH⁻
Result: in addition to the collection of oxygen gas
Electrolysis of aqueous potassium iodide using phenolphthalein indicator and inert electrodes:
Anode: iodide ions are oxidised
2I⁻ - 2e⁻ → I₂
Cathode: molecules of water are reduced (since the K⁺ ions are too stable to be discharged)
2H2O + 2e- → H2 + 2OH-
Result: solid brown iodine will be observed forming at the anode
