Question

Consider the following diagram in which an electrochemical cell is coupled to an electrolytic cell. What will be the polarity of ‘A’ and ‘B’ in the electrolytic cell?

Answer 1

Half cell Reaction

Writing corresponding half-cell reaction for the given cell in the diagram:

(i) At anode: $Zn\left(s\right)\to Z{n}^{2+}\left(aq\right)+2e^{-}$

(ii) At cathode: $C{u}^{2+}\left(aq\right)+2e^{-}\to Cu\left(s\right)$

Overall reaction:
$Zn\left(s\right)+C{u}^{2+}\left(aq\right)\to Z{n}^{2+}\left(aq\right)+Cu\left(s\right)$

Polarity of electrode

From the half-cell reaction we can observe that:

(i) Zn is getting oxidised to $Z{n}^{2+}$ by losing 2 electrons and oxidation of Zn takes place at anode which is negatively charged.

This anode is attached to electrode (A), and electrons travel from anode to electrode (A). Thus electrode (A) is negatively charged.

(ii) $C{u}^{2+}$ is getting reduced to Cu by gaining two electrons and reduction of $C{u}^{2+}$ takes place at cathode which is positively charged. This cathode is attached to electrode (B). Thus electrode (B) is positively charged.

Thus, polarity of electrode (A) is negative while polarity of electrode (B) is positive.