give reasons for the following: electrode potential of anode of a galvanic cell decreases when electrolyte concentration in anode chamber decreases.
The standard electrode potentials (E^0) are the potentials when concentration of the electrolytes is fixed at 1.0M and temperature 298 K. In actual practice, however, the cells operate at widely varying conditions. In such cases the actual value of E is calculated using Nernst equation, given by the general equation: E = E^0 – RT/nF ln [red]/[ox].
For an anode (the electrode where oxidation occurs), the general reaction is:
M ---> M ^n+(aq) + ne-
Corresponding Nernst equation is E = E^0 – RT/nF ln [M]/[M ^n+].
or, E = E^0 + RT/nF ln[M ^n+] (as activity of pure or neat substance is taken as 1).
This is a direct relationship, and it is quite evident that the anode potential (E) increases with rise in [M ^n+] concentration, (better known as electrolyte concentration) and vice versa.