Question

A voltaic cell utilizes the following reaction: 4Fe2+(aq)+O2(g)+4H+(aq)→4Fe3+(aq)+2H2O(l). What is the emf of this cell under standard conditions?

Answer 1

Answer:

0.46 V

Explanation:

The emf for the cell is given by:

Eº cell = Eº oxidation + Eº reduction

From the  given balanced chemical equation, we can deduce that Fe²⁺ has been oxidized to Fe³⁺, and O reduced  from 0 to negative 2, according to the half cell reactions:

4Fe²⁺  ⇒ Fe³⁺ + 4e⁻           oxidation

O₂ + 4H⁺ + 4 e⁻ ⇒ 2 H₂O   reduction

From reference tables for the standard reduction potential, we get

Eº red Fe³⁺ / Fe²⁺   Eºred = 0.77 V  

Eº red O₂ / H₂O      Eºred = 1.23 V

Now all we need to do is change the sign of Eº reduction for the species being oxidized ( Fe²⁺ ) and add it to Eº reduction  O₂:

Eº cell =   Eº oxidation + Eº reduction = - (0.77 V ) + 1.23 V = 0.46 V