Question

Write the half-reactions and cell reaction occurring during electrolysis of each molten salt below.

a) Li⁺ + e⁻ ⟶ Li (s)
b) 2H₂O (l) ⟶ O₂ (g) + 4H⁺ (aq) + 4e⁻
c) 2Na⁺ + 2e⁻ ⟶ 2Na (s)
d) Al³+ + 3e⁻ ⟶ Al (s)

Answer 1

The electrolysis of molten salts produces elements at electrodes through redox reactions. Each reaction involves a reduction at the cathode and oxidation at the anode, leading to the formation of neutral atoms or molecules from ions.

Step-by-step explanation:

The electrolysis of molten salts involves the movement of ions to the electrodes where they gain or lose electrons (redox reactions) to form neutral elements.

• For molten lithium chloride:
  
  • At the cathode (reduction): Li⁺ + e⁻ ⟶ Li (s)
  • At the anode (oxidation): Cl⁻ ⟶ ½ Cl₂(g) + e⁻
  • Overall cell reaction: Li⁺ + Cl⁻ ⟶ Li (s) + ½ Cl₂(g)
• For the electrolysis of water (not a molten salt but included for comparison):
  
  • At the cathode (reduction): 2H₂O (l) + 2e⁻ ⟶ H₂ (g) + 2OH⁻ (aq)
  • At the anode (oxidation): 2H₂O (l) ⟶ O₂ (g) + 4H⁺ (aq) + 4e⁻
  • Overall cell reaction: 2H₂O (l) ⟶ 2H₂ (g) + O₂ (g)
• For molten sodium chloride:
  
  • At the cathode (reduction): 2Na⁺ + 2e⁻ ⟶ 2Na (s)
  • At the anode (oxidation): 2Cl⁻ ⟶ Cl₂(g) + 2e⁻
  • Overall cell reaction: 2Na⁺ + 2Cl⁻ ⟶ 2Na (s) + Cl₂(g)
• For molten aluminum oxide:
  
  • At the cathode (reduction): Al³+ + 3e⁻ ⟶ Al (s)
  • At the anode (oxidation): 2O²⁻ ⟶ O₂(g) + 4e⁻
  • Overall cell reaction: 4Al³+ + 6O²⁻ ⟶ 4Al (s) + 3O₂(g)