Physical Properties of Carboxylic Acids (Edexcel A Level Chemistry): Revision Note

Physical Properties of Carboxylic Acids

Carboxylic acids Carboxylic acid is the name given to the family of compounds that contain the carboxyl functional group, -COOH The general formula of a carboxylic acid is C_nH_2n+1COOH which can be shortened to just RCOOH (In some countries, this family is also called alkanoic acid)

• The nomenclature of carboxylic acid follows the pattern alkan + oic acid, e.g. propanoic acid

• There is no need to use numbers in the name as the carboxyl group, COOH, is always on the number 1 carbon atom

Carboxylic Acids Examples Table

Physical properties of carboxylic acids 

• Carboxylic acids contain two polarised groups

  • C=O and O-H

• This means that the intermolecular forces that carboxylic acids experience are high and they will have relatively high melting points and boiling points

• The presence of the O-H bond means that they can exhibit hydrogen bonding

  • Not only does this contribute to the high melting and boiling points, it also contributes to the solubility in water and other polar solvents of the shorter chained carboxylic acids

• However, solubility falls as the length of the hydrocarbon chain in the carboxylic acid increases

• The hydrocarbon chains are forcing their way between water molecules and so breaking hydrogen bonds between those water molecules

  • Carboxylic acids with more than eight carbon atoms will be solids at room temperature and are very slightly soluble in cold water, but will be more soluble in hot water