Lower fatty acids are easily soluble in water, but with the increase of relative molecular weight, their solubility in water decreases, thus making them soluble or insoluble in water, but soluble in organic solvents.

The longer the carbon chain, the smaller the solubility. For example, methyl, ethyl, propyl and butyric acid are all soluble in water, while the solubility of valeric acid in water is only 2.4% at 20℃; It has been insoluble in water since it was sour.

Carbonic acid, even less soluble in water.