Question

Give the construction of a &lsquo;lead battery&rsquo;. Explain, giving reactions how it can be recharged.

Accepted Answer

The most important secondary cell is the lead storage battery which is commonly used in automobiles and invertors. Generally, a $12 V$ volt lead storage battery is used which consists of $6$ cells. Each cell produces $2 V$ . Each cell consists of a lead anode and a grid of lead packed with lead dioxide. These electrodes are arranged alternatively. They are separated by a thin wooden or fibre glass sheet and suspended in $38 %$ solution of dilute sulphuric acid which acts as an electrolyte. To increase the current output of each cell, anode and cathode plates are joined together, i.e., the cells are connected in parallel.

The cell reactions that occur during discharge are given below:

Anode: $Pb (s) + {SO}_{4}^{2 -} (aq) \to Pb {SO}_{4} (s) + 2 e^{-}$

Cathode: ${PbO}_{2} (s) + {SO}_{4}^{2 -} (aq) + 2 H^{+} (aq) + 2 e^{-} \to {PbSO}_{4} (s) + 2 H_{2} O (l)$

The overall cell reaction consisting of cathode and anode reactions is:

$Pb (s) + {PbO}_{2} (S) + 4 H^{+} (aq) + 2 {SO}_{4}^{2 -} (aq) \to {PbSO}_{4} (s) + 2 H_{2} O (l)$

On charging the battery the electrode reactions are reverse of those that occur during discharge.

Cathode: ${PbSO}_{4} (s) + 2 e^{-} \to Pb (s) + {SO}_{4}^{2 -} (aq)$

Anode: ${PbSO}_{4} (s) + 2 H_{2} O (l) \to {PbO}_{2} (s) + {SO}_{4}^{2 -} (aq) + 2 H^{+} (aq) + 2 e^{-}$

The overall reaction that occurs during recharging is following,

${PbSO}_{4} (s) + 2 H_{2} O (l) \to Pb (s) + {PbO}_{2} (S) + 4 H^{+} (aq) + 2 {SO}_{4}^{2 -} (aq)$

	List-I		List-II
A	$Cd (s) + 2 Ni {(OH)}_{3} (s) \to CdO (s) + 2 Ni {(OH)}_{2} (s) + H_{2} O (l)$	I	Primary battery
B	$Zn (Hg) + HgO (s) \to ZnO (s) + Hg (l)$	II	Discharging of secondary battery
C	$2 {PbSO}_{4} (s) + 2 H_{2} O (I) \to Pb (s) + {PbO}_{2} (s) + 2 H_{2} {SO}_{4} (aq)$	III	Fuel cell
D	$2 H_{2} (g) + O_{2} (g) \to 2 H_{2} O (l)$	IV	Charging of secondary battery

Give the construction of a ‘lead battery’. Explain, giving reactions how it can be recharged.

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