CHAPTER 5. THE CHEMICAL INDUSTRY 5.5
in cars, where they provide the high current that is needed by the starter motor. They
are also used in forkliftsand as standby power sources in telecommunication facilities,
generating stations andcomputer data centres.One of the disadvantages of this type
of battery is that the battery’s lead must be recycled so that the environment doesn’t
become contaminated.Also, sometimes whenthe battery is charging,hydrogen gas
is generated at the cathode and this can cause asmall explosion if the gas comes into
contact with a spark.
The zinc-carbon dry cell ESCCU
A simplified diagram ofa zinc-carbon cell is shown in figure 5.11.
metal capcarbon rod (cathode)zinc casemanganese (IV) oxidepaste of NH 4 Clseparator between zinc
and the electrolyteFigure 5.11: A zinc-carbon dry cellA zinc-carbon cell is made up of an outer zinc container, which acts as the anode. The
cathode is the central carbon rod, surrounded by a mixture of carbon and manganese
(IV) oxide (MnO 2 ). The electrolyte is a paste of ammoniumchloride (NH 4 Cl). A fibrous
fabric separates the twoelectrodes, and a brasspin in the centre of thecell conducts
electricity to the outsidecircuit.
The paste of ammoniumchloride reacts according to the following half-reaction:
2NH+ 4 (aq) + 2e−→ 2NH 3 (g) + H 2 (g)