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What is the standard reduction potential E o for Fe 3 + → Fe ? Given that: Fe 2 + + 2 e - → Fe ; E Fe 2 + / Fe o = - 0 .47 V Fe 3 + + e - → Fe 2 + ; E Fe 3 + / Fe 2 + o = + 0 .77 V

Options

  1. A- 0 .057   V
  2. B+ 0 .30   V
  3. C- 0 .30   V
  4. D+ 0 .057   V

Correct answer

A. - 0 .057   V

Step-by-step solution

i   Fe 3 + → Fe   E 1 o ; ' n ' factor = 3 ΔG 1 ∘ = − 3   × F × E 1 o ii   Fe 3 + + e − → Fe 2 + E 2 o ; 0 . 77 ' n ' factor = 1 ∆ G 2 ∘ = - 1 × F × 0 . 77 iii   Fe 2 + + 2 e − → Fe E 3 o = - 0 . 47 ' n ' factor = 2 ∆ G 3 ∘ = - 2 × F × - 0 . 47 ΔG 1 = ΔG 2 + ΔG 3 − 3 FE 1 o   =   − 1 × 0 .77 × F + 2 × 0 .47 ×

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