Inorganic and Applied Chemistry

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Inorganic and Applied Chemistry

Example 6- I:

Dry cell batteries

For the use in watches and pocket calculators small galvanic cells are used. There are numerous different

types of dry cell batteries. In an acid dry cell battery the inner shell is made of zinc functioning as anode

and a carbon rod in the centre of the cell, being in contact with solid MnO 2 and solid NH 4 Cl functioning as

cathode. The following half cell reaction takes place at the anode:

Zn(s)  Zn2+(aq) + 2 e-

The following half cell reaction takes place at the cathode:

MnO 2 (s) + 2 NH 4 +(aq) + 2 e-  Mn 2 O 3 (s) + 2 NH 3 +H 2 O(l)

Such a galvanic cell produces roughly 1.5 volt which is why it is necessary to insert several dry cell

batteries in series to achieve sufficient voltage to run a pocket calculator. The figure below shows the

principle of the set-up of such an acid dry cell battery.

Figure 6- 7: The dry cell battery

Set-up of the acid dry cell battery.

A more modern version of the dry cell battery is the alkaline version where the solid NH 4 Cl is replaced by

KOH and NaOH. Hereby the following half cell reaction takes place at the anode:

Zn(s) + 2 OH-(aq)  Zn2+(aq) + 2 e- + H 2 O(l)

Electrochemistry