Higher and foundation tiers
Good bases include metal oxides, solid metal hydroxides (remember solutions of metal hydroxides are called alkalis) and
metal carbonates. All these bases can be used to neutralise
acids. Metal carbonates including calcium carbonate and
magnesium carbonate are often used to neutralise acids.
Calcium carbonate is the main ingredient in antacid tablets. Indigestion is caused by too much acid being
produced in the stomach. To neutralise this excess acid a non-toxic base
is need and calcium carbonate
(or chalk) is ideal. Acids react with metal carbonates according to the
equation below:
When metal carbonates reacts with acids they fizz due to the
carbon dioxide gas which is released.
The image opposite shows copper carbonate reacting with hydrochloric acid. The
carbon dioxide gas which is released
can be detected by simply bubbling it through a solution of limewater. The limewater will turn a milky or chalky colour
in the presence of carbon dioxide gas. When the reaction has finished, that is no more bubbles of
carbon dioxide gas are seen
then the acid has been neutralised.
To obtain the solid copper chloride salt
the solution will need to be filtered and evaporated; this is outlined in the diagram below. This simple experiment produced the salt copper chloride; obviously different salts can be produced by
simply using different acids.
The method used to neutralise an acid using a metal carbonate is shown below. It is very similar to the method described earlier using copper oxide as a base. In this example the metal carbonate used is calcium carbonate (chalk) and the acid used is hydrochloric acid.
