When carbon dioxide (CO2) is bubbled through limewater (a solution of calcium hydroxide, Ca(OH)2), it forms a white precipitate of calcium carbonate (CaCO3).

Here's the chemical equation:

CO2 (g) + Ca(OH)2 (aq) → CaCO3 (s) + H2O (l)

Explanation:

* The carbon dioxide gas dissolves in the limewater, forming carbonic acid (H2CO3).

* Carbonic acid then reacts with the calcium hydroxide, forming calcium carbonate and water.

* Calcium carbonate is insoluble in water and precipitates out as a white solid.

This reaction is often used as a test for the presence of carbon dioxide. The formation of the white precipitate indicates that carbon dioxide is present.