Role of electrolytes in a galvanic cell

Question

Suppose we had an electrochemical cell consisting of two half cells each with their own electrodes and electrolytes.

Example:

Zn (s) + 2NO3 (aq) ➡️ Zn(NO3)2 (aq) + 2e

AgNO3 (aq) + e ➡️ Ag(s) + NO3(aq)

In the reduction part of the half cell, the electrolyte (AgNO3) interacts with the Ag electrode as the Ag from the AgNO3 will precipitate onto the electrode as Ag(s). But the function of the electrolyte on the anode part is what confuses me. How does the electrolyte help the zinc give up its electrons? If not, what is its function and what drives zinc to undergo oxidation? Thanks!

Answer 1

You really only need consider the Zn, Zn²⁺, Ag and Ag⁺ to understand what's happening.

The Zn is oxidized and so releases electrons which travel to the cathode(Ag) where the Ag is then reduced. You cannot have Zn²⁺ and Ag⁺ present without a counter anion, and hence the presence of the electrolyte.

Zn(s) | Zn²⁺ || Ag⁺ | Ag(s)

Because the reduction potential for Ag⁺ + e- --> Ag(s) is greater than the reduction potential for Zn²⁺ + 2e- --> Zn(s), the electrons flow from Zn electrode to Ag electrode. Does this makes sense, and does it answer your question? This is what drives Zn to undergo oxidation. It's the difference in reduction potentials between the two metals.