[thedoc (OP)]

TRY asked the Naked Scientists:
   What type of reaction occurs between sulphuric acid and limestone?
What do you think?

[chris]

The answer is, quite a slow one.

Acids react with carbonates to produce carbon dioxide gas and the cation sulphate. But, in this case, the cation is calcium, because limestone is calcium carbonate.

This means that, when the sulphuric acid begins to react with the limestone, it will release some carbon dioxide. But the other product is calcium sulphate. Because this is insoluble, it will form an unreactive layer on the surface of the limestone, preventing access to the carbonate by further hydrogen ions. As such, after the initial fizz, the reaction will slow significantly and proceed only very gently.