ZIMSEC O Level Combined Science Notes:  Lead acid accumulators

• These act as a storage cell
• Electrical energy is passed into the cells during the charging cycle
• It is stored in the form of chemical energy
• $\text{Chemical Energy}\xrightleftharpoons[charging]{discharging} \text{Electrical Energy}$
• Lead acid accumulators are known as secondary cells
• Secondary cells-can be recharged once the voltage drops
• Charging is done by passing a current through the cell in the opposite direction
• This supplies the current
• Inside the lead acid accumulator
• The positive electrode is made up of lead (IV) oxide and
• The electrodes which are in the form of plates are made in grid form
• Sulphuric acid is used as the electrolyte
• When discharging (supplying current)
• Both plates turn to lead and the density of the acid falls
• The voltage of each cell remains constant at 2 V
• Until the battery is nearly drained/completely discharged
• It then drops to 1.8 V
• The state of discharge can be checked using a hydrometer
• The density of a fully charged cell is 1.25 and
• In a flat cell is falls to 1.1
• During the recharging cycle the positive terminal turns back into lead (IV) oxide and
• the density of the acid increases
• Care should be taken during recharging  not to overcharge the cells
• An explosive mixture of hydrogen and oxygen is formed if this occurs
• Distilled water should be added to cover the cells with electrolyte
• The level of the electrolyte should be checked before recharging
• Lead acid accumulators/batteries are often used in cars and
• solar systems

To access more topics go to the Combined Science Notes page.

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