Fred Jones, of Christchurch, asks :-

How is Bicarbonate of Soda made? Is it a mineral or a drug?

Tom Moyle, a chemist with Champion Flour Mills, responded.

Bicarbonate of Soda is made by first dissolving ammonia in a purified brine(salt) solution and then by adding Carbon Dioxide to the mixture. On paper this seems simple but in practice very close control has to be kept on the amount of the various ingredients to ensure that maximum yield is obtained. The Bicarbonate of Soda forms as crystals which are separated from the mix by special filters. Ammonium Chloride is a byproduct from the reaction and this is treated to recover the Ammonia which is recycled for the production of more Bicarbonate of Soda. A further refining step makes the product suitable for human consumption.

A major use of Bicarbonate of Soda is in baking where it is a constituent of Baking Powder. What happens when a cake is heated in the oven is that the gas called Carbon Dioxide is released from the Bicarbonate of Soda (the opposite of the process for making Bicarbonate of Soda) and these gas bubbles expand in the heat and cause the cake to rise.

So Carbon Dioxide is added in the manufacture of Bicarbonate of Soda, and during baking the Carbon Dioxide is driven off. Neat isn't it?

A mineral is a substance obtained by mining and some Bicarbonate of Soda is found in evaporated lakes so it could be considered a mineral. A drug is a substance used for medicinal purposes and because Bicarbonate of Soda is used in some medicines (e.g. for stomach upsets) it could be considered a drug.

As you can see, Bicarbonate of Soda is a very useful substance that is of great benefit to us.