Sodium (Down's Process)

2nd Year Chemistry Notes

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Sodium (Down's Process)

Introduction
On large scale, sodium is manufactured by electrolysis of fused sodium chloride. The process was given by scientist Dawn, therefore, it is called Dawn's Process.


Construction of Down's Cell

A special electrolytic cell known as Dawn's cell is used for the electrolysis of sodium carbonate. The cell consists of a cylindrical shape iron basin lined inside by firebricks. The iron cathode is separated from anode by iron gauze diaphragm. Anode consists of a carbon rod, which is present between two iron cathodes. The electrolytic solution consists of a mixture of sodium chloride (NaCl) and calsium chloride (CaCl2). Calsium Chloride (CaCl2) is added to decrease the melting point of sodium chloride from 801ºC to 600ºC.


Working of Dawn's Cell

When electric current is passed through molten NaCl, the sodium ion migrates towards cathode. It gains and electron and converts into molten sodium metal, which floats inside the cathode compartment. This molten sodium metal is allowed to pass through pipe 'p' which collects it in a vessel 'V' outside the cell.