Page 14 - Curriculum Visions Dynamic Book

Dry cells
The dry cell is a portable form of chemical cell in which the zinc acts
as the case as well as an electrode.
To prevent spillage of liquids, the solutions of the Daniell cell (see page 12) are made into pastes. The dry cell was first made by Georges Leclanché.
The problem with this arrangement is that the zinc is gradually used up
in the reaction, so holes develop in
the case and the cell begins to leak. This is the reason newer “leakproof ” cells were developed.
Alkaline batteries are also Leclanché cells, but with a different electrolyte.
All Leclanché-type batteries have a zinc anode (negative terminal), which also acts as a container, and a carbon and manganese dioxide cathode (positive terminal). The electrolyte
is ammonium chloride. The terminals are separated by a porous material that can be as simple as a sheet of paper.
During use, oxidation takes place at the zinc anode, thereby corroding the zinc case. Manufacturers design the case to be sufficiently thick so that it does
not corrode right through before the electrical energy has been used up.
 A sequence of diagrams to show how the galvanic type of cell shown on page 13 can be modified to make the everyday dry cell. Notice that the copper electrode has been replaced with carbon, zinc forms the case,
and the salt bridge has become a sheet of lining paper. By such modifications the dry cell can be made cheaply. Billions of dry cells are now made each year.

(negative terminal)
(positive terminal)
Salt bridge
Zinc anode
(negative terminal)
Copper cathode
(positive terminal)

Salt bridge
Zinc anode

Zinc anode (negative terminal)
Semipermeable membrane (salt bridge)
Electrolyte paste
Carbon cathode
Carbon cathode (positive terminal)
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