Question

Why copper in transition series only has positive cell potential

Answer 1

Metals react by giving away the electrons, thereby forming positive ions. If we immerse a metal in electrolyte solution following processes may take place:

Metal may leave electrons on the electrode and pass in the electrolyte as metal ion.

in course of time there will be built up of electrons on the metal electrode. This will induce negative charge on the metal, therefore positive ions in the solution will surround the metal electrode.

some of these ions may take back the electron from the electrode and reattach to the electrode.

a dynamic equilibrium will be established when the rate at which ions leaving the electrode surface exactly equals the rate at which they are joining it again.

Now depending up on the ease of giving electrons the magnitude of negative charge on electrode and number of positive ions in the solution surrounding the electrode will vary. ( since Zn is more reactive the -ve charge on electrode and number of Zn (2+) ions in solution surrounding the electrode will be more compared to that of Cu).

If we compare the ease with which following reaction take place

Zn (s) → ← Zn(2+)(aq) + 2e(-)

Cu (s) → ← Cu(2+)(aq) + 2e(-)