Page 26 - Curriculum Visions Dynamic Book

Chemicals from salt
Salt is one of the most important chemicals for modern industry.
It is the starting material from which many other chemicals are made.
One of the most important, efficient and elegant processes for getting products from salt was developed by Hamilton Castner and Karl Kellner at the end of the 19th century. The process involves passing an electric current through brine (salt solution).
During the reaction, which takes places in a container called a diaphragm cell, a number of vital chemicals are produced, as shown by the reaction on this page.
A different process, the Downs process, is used to obtain sodium.
 A diagrammatic representation of the electrolysis process for manufacturing sodium hydroxide.
Strong brine is fed into the cell (usually pumped from rocks).
Sodium ions from the brine pass through and concentrate the sodium hydroxide, leaving chloride ions.
Chloride ions are converted to chlorine atoms which form chlorine molecules (Cl2) – chlorine gas.
This part of the cell is kept under pressure.
Chlorine gas is given off.
The diaphragm: a membrane through which only sodium ions can pass. Asbestos was the first material used, but modern cells use a form of plastic (polymer).
Positive electrode (anode) made from titanium coated with platinum.
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Electricity supply