Batteries, changing/charging

Fig. 8M The potential of the two electrodes in a CiilZn battery during charge and discharge. Note that the polarity of the cell is not changed, although the potential it delivers is always smaller than the potential needed to charge it. Reprinted with permission from Moran and Gileadi, J. Chem. Education, 66, 912. 1989). Copyright 1989, Division of Chemical Education of the American Chemical Society.

When the battery is discharging, metallic lead oxidizes into lead sulfate and lead oxide is reduced to lead sulfate. Therefore, lead sulfate forms at both electrodes. At the same time, sulfuric acid is consumed and water is produced so that the density of sulfuric acid falls as discharging progresses. The state of the battery s charge can then be determined by this change of density. 

In the lead-acid battery, the positive and negative terminals (coloured red and black or blue, respectively) are fixed. However, they change their role as anode or cathode depending on whether the battery is charging or discharging. In both cases, a reduction half reaction occurs at the cathode and an oxidation half reaction at the anode. 

The chemical hazards at the worksite that may cause one to need an eye wash or safety shower. Examples include dipping and coating operations, powered industrial truck battery changing and charging areas, and methylene chloride handling. 

Fuel cells differ from batteries in that they consume reactants, which must be replenished, while batteries store electrical energy chemically in a closed system. Additionally, while the electrodes within a battery react and change as a battery is charged or discharged, a fuel cell s electrodes are catalytic and relatively stable. 

In the lead accumulator the electrode plates are lead grids, filled initially with a paste of lead oxide PbO. They are placed in an electrolyte of dilute sulfuric acid. One electrode plate is marked plus , the other minus . The battery is charged with dc current from a rectifier. In this process the plus plate is connected to the positive pole of the rectifier, the minus plate to its negative pole. On the plus plate the lead oxide is changed to lead dioxide PbOj, and on the minus plate metallic lead is formed. Be-... 

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