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Indigestion remedies rely on a tablet or liquid, typically containing bases such as sodium hydrogen carbonate (baking soda) or calcium carbonate, which neutralise the build-up of extra stomach acid that causes the discomfort. This neutralisation relieves the symptoms. Reactions of acids with carbonates are another widely useful type of reaction.

metal carbonate + acid _↓ water + carbon dioxide + metal salt

The acid, once again, donates the hydrogen ions (H⁺) that react with the carbonate ions (CO₃^2–) producing water and carbon dioxide.

What is the word equation for each of the following examples? As before, think about the usual products of this type of reaction and then what is left as a salt.

sodium hydrogen carbonate with hydrochloric acid?

sodium hydrogen carbonate + hydrochloric acid _↓ water + carbon dioxide + sodium chloride

calcium carbonate with hydrochloric acid?

calcium carbonate + hydrochloric acid _↓ water + carbon dioxide + calcium chloride

How might you show the class that the other product of the reaction of carbonates with acids is indeed carbon dioxide?

Allow the evolved gas to bubble into a test tube of limewater. The limewater will change in appearance from colourless to cloudy white or 'milky', as usual in this characterisic test for carbon dioxide.

When might an acid not react with a carbonate?

If the acid is a weaker acid than H₂CO₃.

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There are reminders of this very reaction, acids and carbonates, in everyday life – we can see that monuments and buildings made from carbonate rocks have incurred damage from acid rain. An experimental investigation can be undertaken by students to identify and record evidence of the effects of acid rain in their local environment.