Question

What is the sulphuric acid concentration of a fully charged battery electrolyte?

Answer 1

1. Electrolytes are substances that have the ability to produce an electrically conductive solution by dissolving polar solvents like water.
2. By dissolving the electrolytes into the solution they will dissociate to form cations and anions and completely disperse into the solution.
3. Lead-acid batteries are consisting of sulphuric acid $\left({\mathrm{H}}_2{\mathrm{SO}}_4\right)$ solution in water and lead plates which are separated by this solution.
4. These types of batteries are rechargeable batteries.
5. When the batteries are discharged, i.e. battery is being used then the electrons will move from the negatively charged plate to the positively charged plate.
6. The reaction on a negatively charged plate and positively charged plate are shown below.
7. Negatively charged plate reaction:
   $\mathrm{Pb}\left(\mathrm{s}\right)+{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)\to {\mathrm{PbSO}}_4\left(\mathrm{s}\right)+2{\mathrm{H}}^{+}\left(\mathrm{aq}\right)+2{\mathrm{e}}^{-}$
8. Positively charged plate reaction:
   ${\mathrm{PbO}}_2\left(\mathrm{s}\right)+{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)+2{\mathrm{H}}^{+}\left(\mathrm{aq}\right)+2{\mathrm{e}}^{-}\to {\mathrm{PbSO}}_4\left(\mathrm{s}\right)+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$
9. The overall reaction occurs as follows:
   $\mathrm{Pb}\left(\mathrm{s}\right)+{\mathrm{PbO}}_2\left(\mathrm{s}\right)+2{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)\to 2{\mathrm{PbSO}}_4\left(\mathrm{s}\right)+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$
10. If the battery is fully charged then lead is considered to be a negatively charged plate, and lead oxide is a positively charged plate.
11. If in case the battery is overcharged then water gets electrolyzed and the formation of oxygen and hydrogen gas takes place.
12. In this battery concentrated $35\%$of sulphuric acid is used and $65\%$of water.
13. Thus, a fully charged battery $35\%$of sulphuric acid is used as an electrolyte.