Electrochemistry

Standard electrode potentials are Fe2+/Fe [ E = -0.44 V] and Fe3+/Fe2+ [ E = 0.77 V]; If Fe2+, Fe3+ and Fe blocks are kept together, then

1. Fe3+ increases
2. Fe3+ decreases
3. Fe2+/Fe3+ remains unchanged
4. Fe2+ decreases.

Answer

(2) Fe3+ decreases

Solution

The couple with the lower reduction potential acts as anode (oxidation) and the one with the higher potential as cathode (reduction).

Anode: Fe Fe2+ + 2e-

Cathode: 2Fe3+ + 2e- 2Fe2+

E cell = E cathode - E anode

= 0.77 - (-0.44)

= 1.21 V

E cell is positive, so the reaction Fe + 2Fe3+ 3Fe2+ is spontaneous.

Fe3+ decreases (and Fe2+ increases).

Answer: (2)