4.4.3.4 Electrolysis of aqueous solutions

What does aqueous mean

Dissolves In water

What do water molecules ionise to form

Hydrogen ions and hydroxide ions

Equation for ionising water

H₂O ⇌ H⁺ + OH⁻

Ions in copper sulphate solution

CuSO₄

Cu²⁺

SO₄²⁻

H⁺

OH⁻

(Because dissolved in water)

With copper sulphate solution what happens at the cathode

Cu²⁺ And H⁺ is attractive to negative electrode

Copper less reactive than hydrogen so it is produced at cathode

Rule for element reduced at cathode

Hydrogen is produced at the cathode If metal is more reactive than hydrogen

2H⁺ + 2e⁻ —> H (reduced)

With copper sulphate solution what happens at the cathode

Make

Rule for element oxidised at anode

If the aqueous solution contains halide ions then the halogen will be produced at the anode

4OH⁻—> O₂ + 2H₂O + 4e⁻ (Oxidised)

4OH⁻ - 4e⁻ —> O₂ + 2H₂O (Oxidised¹)

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Why is platinum used for electrode

It is inert- unreactive

Half equation at cathode for copper sulphate solution

Cu²⁺ + 2e⁻ → Cu (reduced)

Half equation at anode for copper sulphate solution

4OH⁻—> O₂ + 2H₂O + 4e⁻ (Oxidised)

4OH⁻ - 4e⁻ —> O₂ + 2H₂O (Oxidised¹)

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Ions in sodium chloride

NaCl

Na⁺

Cl⁻

H⁺

OH⁻

What happens at cathode during electrolysis of sodium chloride solution

H⁺ and Na⁺ is attracted to cathode

Hydrogen is produced as it is more reactive than sodium

2H⁺ + 2e⁻ —> H (reduced)

What happens at anode during electrolysis of sodium chloride solution

Cl⁻ and OH⁻

Cl gas Is produced be it is a halide

2Cl⁻ → Cl₂ + 2e⁻ ( oxidation)

2Cl⁻ - 2e⁻ → Cl₂ ( oxidation)