Electrolysis
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Define electrolysis
splitting up of a substance into its elements using electricity
What type of substance can undergo electrolysis?
ionic compounds as they can be made to conduct electrcity
A substance can only be electrolysed once…
melted as ions are free to move or dissolve in water
Why are electrodes needed? What are they made of?
needed to complete the circuit made of graphite which can conduct electricity and has low reactivity
What is the positive electrode called?
anode
What is the negative electrode called?
cathode
What happens during molten electrolysis?
electrolyte heated (ensure compound stays heated) anode attracts anions (-) cathode attracts cations (+)
molten magnesium bromide (electrolyte) What are the half equations? Mg⁺² and Br⁻¹
Br⁻¹ goes to anode 2Br⁻¹ → 2e⁻ +Br₂ Mg⁺² goes to cathode Mg⁺² + 2e⁻ → Mg
molten magnesium bromide What is observed at each electrode?
negative electrode: Mg ion gains 2e⁻ to form Mg atom so grey solid formed positive electrode: bubbles, brown gas given off
What are the negatives of molten electrolysis?
Requires lots of energy ∴ expensive ↳ environmental problems
Why is copper a good conductor of electricity?
has delocalised electrons that can move
KCl (K⁺, Cl⁻) What are the half equations? What is observed at each electrode?
negative: K⁺ + e⁻ → K (grey solid) positive: 2Cl⁻ →Cl₂ + 2e⁻ (bubbles, green gas)
MgO (Mg⁺², O⁻²) What are the half equations? What is observed at each electrode?
negative: Mg⁺² + 2e⁻ → Mg (grey solid) positive: 2O⁻² → 4e⁻ + O₂ (bubbles)
AgI (Ag ⁺¹, I ⁻¹) What are the half equations? What is observed at each electrode?
negative: Ag⁺¹ + e⁻ → Ag (silver solid) positive: 2I⁻¹ → 2e⁻ + I₂ (bubbles, purple gas)
Fe₂O₃ (Fe⁺³, O⁻²)
negative: Fe⁺³ + 3e⁻ → Fe (grey solid) positive: 2O⁻² → 4e⁻ + O₂ (bubbles)
PbBr₂ (Pb⁺², Br⁻) What are the half equations? What is observed at each electrode?
negative: Pb⁺² + 2e⁻ → Pb (grey solid) positive: 2Br⁻ → 2e⁻ + Br₂ (bubbles, brown gas)
Solution electrolysis Positive electrode rule?
Halogen or oxygen Halogen takes priority
Solution electrolysis Negative electrode rule?
X or hydrogen is produced The less reactive one is produced
What is produced in this solution electrolysis? NaCl
Positive electrode: (Cl⁻, OH⁻) Cl₂ produced 2Cl⁻ → 2e⁻ + Cl₂ Negative electrode: (Na⁺, H⁺) Na more reactive ∴ H produced 2H⁺ + 2e⁻ → H₂ Left over: NaOH
What is produced in this solution electrolysis? CuSO₄
positive electrode: 4OH⁻ → O₂ + 2H₂O + 4e⁻ observations: bubbles negative electrode: Cu⁺² + 2e⁻ → Cu observations: brown solid Whats left? H₂SO₄