Carbon monoxide, like the isoelectronic molecule, is barely soluble in water. Carbon dioxide dissolves easily in water to form carbonic acid:



This is a weak acid with a sharp taste, familiar from carbonated soft drinks. The bubbles in a carbonated drink are incompletely dissolved gas.

When dissolves in water, the carbon atom attracts a lone pair from the oxygen of a water molecule and forms carbonic acid, which has the structure shown on the next page. The carbon atom is double-bonded to one oxygen atom, and single-bonded to each of two OH groups.

Since carbon is moderately electronegative and the C-O bond in C-O-H is stronger than the O-H bond, the carbonic acid molecule dissociates in water by losing protons, and therefore is an acid. Dissociation takes place in two steps: