Question

Given that $Eº_{Fe^{3 +}/Fe^{2 +}}$= –0.36 V and $Eº_{Fe^{2 +}/Fe}$= – 0.439 V respectively. Therefore value of $Eº_{Fe^{3 +},Fe^{2 +}/Pt}$ is :

• A. (–0.036 – 0.439) V
• B. (–0.036 + 0.439) V
• C. [3(– 0.036) + 2(–0.439)] V
• D. [3(–0.036) – 2 (–0.439)] V

Answer 1

Answer: (D)

$3(–0.036) – 2 (–0.439)$ V

Answer 2

Fe³⁺ + 3e ® Fe DGº₁ = – 3 F (–0.36) V

Fe²⁺ + 2e ® Fe DGº₂ = – 2 F (–0.439) V

Fe³⁺ + e ® Fe²⁺ DGº_net = DGº₁ – DGº₂

or DGº_net = – F [3 (–0.36 – 2 (–0.439)] V

or Eº = [3 (–0.36) – 2 (–0.439)] V