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General Chemistry Principles, Patterns, and Applications, 2011

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cathode : PbO2 s<br />

- ® PbSO4 s<br />

Equation 19.91<br />

anode : Pb s<br />

® PbSO4 s<br />

Equation 19.92<br />

overall : Pb s<br />

( ) + HSO4 - ( aq) + 3H + ( aq) + 2e<br />

( ) + 2H 2O( l) E cathode = 1.685 V<br />

( ) + HSO4 - ( aq)<br />

( ) + H + ( aq) + 2e - E anode = -0.356 V<br />

( ) + PbO2( s) + 2HSO4 - ( aq) + 2H + ( aq)<br />

( ) E cell = 2.041 V<br />

® 2PbSO4(s) + 2H 2O l<br />

Figure 19.15 One Cell of a Lead–Acid Battery<br />

The anodes in each cell of a rechargeable battery are plates or grids of lead containing spongy lead<br />

metal, while the cathodes are similar grids containing powdered lead dioxide (PbO2). The<br />

electrolyte is an aqueous solution of sulfuric acid. The value of E° for such a cell is about 2 V.<br />

Connecting three such cells in series produces a 6 V battery, whereas a typical 12 V car battery<br />

contains six cells in series. When treated properly, this type of high-capacity battery can be<br />

discharged <strong>and</strong> recharged many times over.<br />

As the cell is discharged, a powder of PbSO4 forms on the electrodes. Moreover, sulfuric acid is consumed<br />

<strong>and</strong> water is produced, decreasing the density of the electrolyte <strong>and</strong> providing a convenient way of<br />

monitoring the status of a battery by simply measuring the density of the electrolyte.<br />

Saylor URL: http://www.saylor.org/books<br />

Saylor.org<br />

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