Question

Standard reduction potentials of the two electrodes Co²⁺/Co and Fe²⁺/Fe are -0.28 V and -0.44 V respectively. The EMF of the cell for which cell reaction is Co + FE²⁺ → Co²⁺ + Fe will be
1. -0.16 V
2. -0.72 V
3. +0.72 V
4. +0.16 V

Answer 1

Correct Answer - Option 1 : -0.16 V

Explanation - 

• Fe²⁺ + 2e^- à Fe ----------- (1) Efe²⁺ I Fe = 0.44 V
• Co²⁺ + 2e^- à Co ^– (2) Eco2+ I Co = - 0.274V
• Net reaction –
  • Fe²⁺ + Co à Fe + Co²⁺
  • ΔG⁰_net = ΔG1 – ΔG2
• Which gives,
  • −nFEnet ​=−n11FE1​−(−n2FE⁰₂​)
  • n₁ = 2
  • n₂ = 2
• For the resultant equation, n = 2
  • E⁰_net = 2E⁰₁ + (-2E⁰₂)/2 = -0.44 + 0.28
  • E0net  = - 0.16 V