Question

Which liquid is used in a battery?

Answer 1

Dilute Sulphuric acid $(H_2SO_4 \,in\, H_2O)$ is the liquid electrolyte which is used in batteries. Sulphuric acid is a strong acid which dissociates completely into ions in water. Owing to this property, sulphuric acid proceeds with the charging –discharging process smoothly in the battery.

Complete answer:
Approximately 30 % to 50 % sulphuric acid solution in water is used as electrolyte in batteries. Let us consider the lead-acid battery. In this battery, lead $(Pb)$ , lead oxide $(PbO_2)$ are used as electrodes and dilute sulphuric acid is used as an electrolyte. In water, $H_2SO_4$ is completely dissociated and produces hydrogen ion $\left( {{H}^{+}} \right)$ and sulphate ion ${SO_4}^{2-}$. These ions are reacted with $Pb$ and $PbO_2$ and produce $PbSO_4$ which is sparingly soluble in water. Hence, the concentration of $H_2SO_4$ in the water goes on decreasing. In this way, the battery gets discharged. On the other hand, during the charging process, $PbSO_4$ which is produced at both anode and cathode gets converted into $Pb$ and $PbO_2$ with simultaneously generation of hydrogen ion $\left( {{H}^{+}} \right)$ and sulphate ion ${SO_4}^{2-}$ . Hence, the concentration of $H_2SO_4$ in the water goes on increasing and the battery gets charged.

Additional Information:
Besides certain advantages of using dilute sulphuric acid as electrolyte in batteries, it has few limitations which includes its corrosive nature and dangerous liquid to handle.

Note:
It is important to note that dilute sulphuric acid is used as liquid electrolyte in batteries. $H_2SO_4$ is a strong acid which dissociates completely in water and produces hydrogen ion $\left( {{H}^{+}} \right)$ and sulphate ion $(SO{{4}^{2-}})$ . These ions allow the proceeding of the charging –discharging process smoothly in the battery.