The functional group of carboxylic acids is the carboxyl group -COOH. These are weak acids found widely in nature. Carboxylic acids with between one and four carbon atoms are very soluble in water as the polar C=O and OH groups form hydrogen bonds with water molecules.Carboxylic acids undergo typical acid reactions with metals, carbonates and bases to form salts called carboxylates.Ethanoic acid reacts with sodium to form sodium ethanoate CH3COONa and hydrogen gas. On reaction with sodium hydroxide, sodium ethanoate and water are formed. On reaction with sodium carbonate carbon dioxide and water are formed in addition to the salt.