Question

In galvanic cells why anode is negative and the cathode positive?

Answer 1

Galvanic cell:-

• It is a type of cell that converts the chemical energy produced in a spontaneous redox reaction into electrical energy.
• Due to this, a Galvanic cell is also called an electrochemical cell.
• We know that oxidation takes place at the anode.
• For example, if we consider the reaction between Zinc and Copper ions which forms Zinc ions and copper metal:

$\underset{\mathrm{Zinc}}{\mathrm{Zn}\left(\mathrm{s}\right)}+\underset{\mathrm{Copper}\mathrm{ion}}{{\mathrm{Cu}}^{2+}\left(\mathrm{aq}\right)}\to \underset{\mathrm{Zinc}\mathrm{ion}}{{\mathrm{Zn}}^{2+}\left(\mathrm{aq}\right)}+\underset{\mathrm{Copper}}{\mathrm{Cu}\left(\mathrm{s}\right)}$

• The zinc metal gets oxidized to zinc ions by losing 2 electrons at the cathode.
• Reaction at the cathode:

$\underset{\mathrm{Zinc}}{\mathrm{Zn}\left(\mathrm{s}\right)}\to \underset{\mathrm{Zinc}\mathrm{ion}}{{\mathrm{Zn}}^{2+}\left(\mathrm{aq}\right)}+\underset{\mathrm{Electrons}}{2{\mathrm{e}}^{-}}$

• The copper ions get reduced to copper metal by gaining 2 electrons at the anode.
• Reaction at the anode:

$\underset{\mathrm{Copper}\mathrm{ions}}{{\mathrm{Cu}}^{2+}\left(\mathrm{aq}\right)}+\underset{\mathrm{Electrons}}{2{\mathrm{e}}^{-}}\to \underset{\mathrm{Copper}}{\mathrm{Cu}\left(\mathrm{s}\right)}$

• Hence the anode has a negative potential and thus acts as negative in an electrochemical cell or galvanic cell.
• But on the other hand in the electrolytic cell, the anode is connected to the positive terminal of the battery.
• Hence the anode acts as a positive in the electrolytic cell.