DOWN'S PROCESS

INTRODUCTION:

J.C Down developed a process for the manufacture of sodium metal known as DOWN's Process.

PRINCIPLE:

The process based upon the principle of electrolysis of Aqeous sodium chloride solution

 NaCl     →   2Na + Cl2

RAW MATERIALS:

• Fused sodium chloride is used as the electrolyte in the process.
• As the sodium chloride is has the melting point of 801 degree celcius some amount of calcium chloride is added to lower the melting point to about 600 degree celcius which makes the process feasible.

Working:

When an electric current is passed through the molten mixture of NaCl and CaCl2, NaCl decomposes in to   Na+ and Cl- ion. Na+ ions migrate towards cathode while Cl- ions towards the anode. The molten sodium   collects in the cathode compartment where it rises to the top and is tapped off by a pipe. Chlorine is   collected at the anode.

ELECTROCHEMICAL CHANGES

 At cathode

 

Na+-ions migrate to cathode where they are reduced to Na.

2Na+ + 2e    →  2Na (Reduction)

At anode 

Cl--ions migrate to anode and oxidised to form chlorine gas.

2Cl-   →  Cl2 + 2e- (Oxidation)

Overall Reaction

 2Na+ + 2e-    →   2Na

2Cl-   →  Cl2 + 2e-

__________________ 

2Na+ + 2Cl-   →  2Na + Cl2

 During electrolysis calcium is also obtained at cathode but sodium and calcium are separated from each other due difference in density. Density of Na is 0.67gm/cc and the density of Ca is much higher than that of Na i.e. 2.54gm/cc. That's why they do not mix with each other.

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