The chemistry behind the modern day car battery

View the introductory video on the right.
The chemical reactions that take place in the car battery

An electrolyte is a solution that

The positive terminal of a car battery is lead impregnated with and

The negative terminal of a car battery is covered in and

When the terminals are connected by the electrolyte what flows through the circuit?

Video sourced at 26/03/20 8.30pm

The modern day car battery is composed of lead and sulfuric acid. The beauty of this type of battery is that it can be recharged. Rechargeable batteries are known as secondary cells.

The anode of the battery is lead metal while the cathode is made up of lead impregnated with lead(IV)oxide.

During discharge the chemical reaction that takes place:
- at the anode, negative electrode, is
Pb(s) + SO4-2(aq) => PbSO4(s) + 2e-

- at the cathode, positive electrode, is
PbO2(s) + SO4-2(aq) + 4H+(aq)+ 2e- => PbSO4(s) + 2H2O(l)

During recharging the chemical reaction that takes place at the

- anode, positive electrode, is

: PbSO4(s) + 2H2O(l) → PbO2(s) + 4H+(aq) + SO42-(aq) + 2e-

- cathode, negative electrode, is

PbSO4(s) + 2e- → Pb(s) + SO42-(aq)

During discharge sulfuric acid is used up and lead sulfate is deposited on both electrodes. The battery becomes "dead" when the electrodes are fully covered with lead sulfate. By passing a current in the reverse direction, to the flow during discharge, the battery can be recharged. Recharging reverses both reactions occuring at each electrode. This results in sulfuric acid been regenerated and lead sulfate been removed from the electrodes.

Write the overall reaction of the lead acid accumulator.

What happens to the pH of the electrolyte as the battery discharges?

Knowing that oxidation always occurs at the anode and reduction always occurs at the cathode give reactions at the anode and cathode when recharging is taking place.


Activity-make a lead acid accumulator
Continue with a discussion on recharging secondary cells