Page "Carbonate" Paragraph 16

In aqueous solution, carbonate, bicarbonate, carbon dioxide, and carbonic acid exist together in a dynamic equilibrium.

In strongly basic conditions, the carbonate ion predominates, while in weakly basic conditions, the bicarbonate ion is prevalent.

In more acid conditions, aqueous carbon dioxide, ( aq ), is the main form, which, with water,, is in equilibrium with carbonic acid-the equilibrium lies strongly towards carbon dioxide.

Thus sodium carbonate is basic, sodium bicarbonate is weakly basic, while carbon dioxide itself is a weak acid.

Note that although the carbonate salts of most metals are insoluble in water, the same is not true of the bicarbonate salts.

This equilibrium between carbonate, bicarbonate, carbon dioxide and carbonic acid in water can, under changing temperature or pressure conditions, and in the presence of metal ions with insoluble carbonates, result in formation of insoluble compounds.

This is responsible for the buildup of scale inside pipes caused by hard water.