DEFECTS OF A PRIMARY CELLS, POLARIZATION AND LOCAL ACTION

DEFECTS OF A PRIMARY CELLS, POLARIZATION AND LOCAL ACTION

1. Polarization : this is the process whereby hydrogen gas bubbles are produced around the copper plate of the cell. When the zinc electrodes react with Tetraoxosulphate vi acid  the Hydrogen bubbles are produced. The effect of this is the production of back E.m.f which reduces the current in the external circuit .

This effect can be reduced by brushing the plates or by using depolarizer. An example of depolarizer is manganese dioxide   or potassium dichlorate . They oxidized the hydrogen bubbles to form water thereby remove the hydrogen in the process

1. Local action:  this occur when the zinc plate worn because of the impurities in the zinc plate electrodes. These impurities are iron and carbon which sets up tiny cells around the zinc plates electrodes and dissolves the electrode along the process producing bubbles of hydrogen.

Local action can be prevented by amalgamation.

Amalgamation is the process of cleaning the zinc with Tetraoxosulphate vi acid  and then rubbing it with mercury which cover up the impurities and prevent their contact with the acid.

SECONDARY CELLS, ACCUMULATORS