Page 28 - Curriculum Visions Dynamic Book

Lead in batteries
One of the biggest users of lead and lead oxide is the storage battery industry. The main plates used in lead-acid batteries are made from grids of lead alloy, alternate plates being coated with “spongy” lead and lead oxide.
The lead-acid battery is made of a number of units,
each called cells. Every cell in a lead-acid battery can generate approximately 2 volts of electricity. In a car battery, six cells are placed in series, producing a total of about 12 volts.
Bubbles of gas seen during charging are due to the splitting of some water molecules into oxygen and hydrogen gases.
Negative electrode made of lead
 The battery is fully charged.
The negative electrode is formed of spongy lead, and the positive electrode is lead dioxide. The concentration of sulphuric acid is at a maximum.
 A lead-acid storage battery in a vehicle engine compartment.
Sulphuric acid electrolyte
Positive electrode made of lead dioxide
Lead sulphate deposited on both electrodes
 The battery is being discharged through use.
The two electrode materials begin to be converted to lead sulphate. The concentration of sulphuric acid is decreasing.
EQUATION: Discharging (using) a lead-acid battery
Lead + lead dioxide + sulphuric acid ➪ lead sulphate + water Pb(s) + PbO2(s) + 2H2SO4(aq) ➪ 2PbSO4(s) + 2H2O(l)
EQUATION: Charging a lead-acid battery
Lead sulphate + water ➪ lead + lead dioxide + sulphuric acid 2PbSO4(s)+ 2H2O(l) ➪ Pb(s) + PbO2(s) + 2H2SO4(aq)
 The battery is fully discharged. The electrodes are now covered with lead sulphate, and the sulphuric acid concentration is very low. (Charging the battery using a generator will return the battery to the state in .)
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