Question

Explain the construction and working of a voltaic cell.

Answer 1

• A voltaic cell is an electrochemical cell that converts chemical energy to electrical energy.
• Construction: It consists of a glass vessel with dilute sulphuric acid present in it which is called an electrolyte. Two plates one made of zinc which acts as the negative electrode and the other is made of copper which acts as the positive electrode.

1. Working: Electrodes are connected with conducting wire and a bulb in between them. The dilute sulphuric acid present in the glass vessel is dissociated into its ions

$$\begin{gathered} {\mathrm{H}}_2{\mathrm{SO}}_4\rightleftharpoons 2{\mathrm{H}}^{+}+{\mathrm{SO}}_4^{2-} \\ (\mathrm{Dilute}\mathrm{sulphuric}\mathrm{acid})(\mathrm{Hydrogen}\mathrm{ions})(\mathrm{Sulphate}\mathrm{ions}) \end{gathered}$$

2. The zinc plate is more electropositive compared to copper, loses electrons, and gets ionized.

$$\begin{gathered} \mathrm{Zn}\to {\mathrm{Zn}}^{2+}+2{\mathrm{e}}^{-} \\ \left(\mathrm{Zinc}\right)(\mathrm{Zinc}\mathrm{ions})\left(\mathrm{Electrons}\right) \end{gathered}$$

3. When each zinc gets ionized, two free electrons are produced.

4. The negative charges are accumulated over the zinc plate.

5. The positive zinc ions formed due to ionization move into the electrolyte and repel hydrogen ions which get accumulated on the copper plate.

6. The free electrons accumulated on the zinc plate pass through the wire through the bulb and make the bulb glow then reach the copper plate.

7. At the copper plate, these electrons combine with positive hydrogen ions and get neutralized to form molecular hydrogen and evolve as gas.

8. The zinc ions $\left({\mathrm{Zn}}^{2+}\right)$ move into the electrolyte from the zinc plate and combine with sulfate ions $\left({\mathrm{SO}}_4^{2-}\right)$ to form zinc sulfate.

9. $$\begin{gathered} {\mathrm{Zn}}^{2+}+{\mathrm{SO}}_4^{2-}\to {\mathrm{ZnSO}}_4 \\ (\mathrm{Zinc}\mathrm{ions})(\mathrm{Sulphate}\mathrm{ions})(\mathrm{Zinc}\mathrm{sulphate}) \end{gathered}$$

10. As negative charges are accumulated at the zinc plate, it is at a lower potential and the copper plate is at a higher potential.

11. This potential difference makes the flow of electrons through the wire and an electric current is produced.

12. After some time, the whole of sulphuric acid (H2SO4) is consumed, and the electric current is established in the external conducting wire until all the sulphuric acid is used up.