MYP Chemistry sample question: Electrolysis of molten compounds

Molten lead(II) bromide (PbBr₂) is electrolysed using inert electrodes.

1. (a)Explain why the lead(II) bromide must be molten.[1]
   Show the mark scheme for (a)

   • • The ions are free to move and carry the current in the liquid state (1)
2. (b)Name the product at the cathode and explain how it forms.[2]
   Show the mark scheme for (b)

   • • Lead (1)
   • • Pb²⁺ ions are attracted to the cathode and gain electrons (reduction) (1)
3. (c)Name the product at the anode and write the half-equation for its formation.[3]
   Show the mark scheme for (c)

   • • Bromine (1)
   • • 2Br⁻ → Br₂ + 2e⁻ (2: one for correct species, one for balancing)

Remember OIL RIG: oxidation is loss of electrons (at the anode) and reduction is gain (at the cathode).