lectrochemistry: Primary and Secondary Batteries

A Secondary Battery: The Lead Storage Battery

The electrodes of the cells in a lead storage battery consist of lead grids. The openings of the anodic grid is filled with spongy (porous) lead. The openings of the cathodic grid is filled with lead dioxide {PbO₂}. Dilute sulfuric acid {H₂SO₄} serves as the electrolyte. When the battery is delivering a current, i.e.discharging, the lead at the anode is oxidized:

Pb Pb²⁺ + 2 e^–

Because the lead ions are in the presence of aqueous sulfate ions (from the sulfuric acid), insoluble lead sulfate precipitates onto the electrode. The overall reaction at the anode is therefore:

Pb + SO₄^2– PbSO₄ (electrode) + 2 e^–

Electrons that flow from the anode simultaneously reduce the lead dioxide at the cathode:

2 e^– + PbO₂ + 4 H⁺ Pb²⁺ + 2 H₂O

Again, the lead ions that are formed react with aqueous sulfate ions to form insoluble lead sulfate on the electrode, and the overall reaction at the cathode is:

2 e^– + PbO₂ + 4 H⁺ + SO₄^2– PbSO₄ (electrode) + 2 H₂O

What is the overall equation for the lead storage battery when it is discharging?

Write your answer on a piece of paper. When finished, click on the green checks to reveal answers for each step.

	Net anode:
	Net cathode:
	Overall:

The lead storage cell can be recharged by passing a current in the reverse direction. The half-reactions are the exact reverse of those that occur when the cell is operating as a voltaic cell.

Primary and Secondary Batteries