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Describe about lead storage battery construction and its uses. |
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Answer» Solution :Lead storage battery : 1. Anode `"":""` Spongy lead CATHODE `":"`Lead plate bearing `PbO_(2)` Electrolyte `":"`38% by mass of `H_(2)SO_(4)` with density 1.2 g/ml 2. Oxidation occurs at the anode `""Pb_((s)) rarr Pb^(2+)""_((aq))+2e^(-)".................(1)"` The `Pb^(2+)` ions combine with `SO_(4)""^(2-)` to form `PbSO_(4)` PRECIPITATE `""Pb^(2+)""_((aq))+SO_(4)""^(2-) rarr PbSO_(4(s))".....................(2)"` 3. Reduction occurs at the cathode `""PbO_(2(s))+4H^(+)""_((aq))+2e^(-) rarr Pb^(2+)""_((aq))+2H_(2)O_((l))"....................(3)"` The `Pb^(2+)` ions also combines with `SO_(4)""^(2-)` ions to form sulphuric acid to form `PbSO_(4)` Precipitate `""Pb^(2+)""_((aq))+SO_(4)""^(2-)""((aq)) rarr PbSO_(4)"......................(4)"` 4. The overall reaction is, `(1)+(2)+(3)+(4)` `Pb_((s))+PbO_(2(s))+4H^(+)""_((aq))+2SO_(4)""^(2-)""_((aq)) rarr 2PbSO_(4(s))+2H_(2)O_((l))` 5. The emf of a single cell is about 2V. Usually six such cells are combined in series to produce 12 volts. 6. The emf of the cell depends on the concentration of `H_(2)SO_(4)`. As the cell reaction uses `SO_(4)""^(2-)` ions, the concentration `H_(2)SO_(4)` decreases. When the cell potential falls to about 1.8 V, the cell has to be recharged. 7. Recharge of the cell: During recharge process, the role of anode and cathode is reversed and `H_(2)SO_(4)` is regenerated. Oxidation occurs at the cathode (now anode) `overset(+2)(PbSO_(4(s)))+2H_(2)O_(l) rarr overset(+4)(PbO_(2(s)))+4H^(+)""_((aq))+overset(2-)(SO_(4(aq)))+2e^(-)` Reduction occurs at anode (now cathode) `PbSO_(4(s))+2e^(-) rarr Pb_((s))+SO_(4)""^(2-)""_((aq))` Overall reaction `2PbSO_(4(s))+2H_(2)O_((l)) rarr Pb_((s))+PbO_(2(s))+4H^(+)""_((aq))+2SO_(4)""^(2-)""_((aq))` The above reaction is exactly the reverse of redoxreaction which TAKES place while discharging. 8. Uses: Lead storage battery is usedin automobiles, trains, inverters. |
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