Edexcel A Level Chemistry:复习笔记7.3.1 Physical Properties of Carboxylic Acids

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 CnH2n+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

7.3.1-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

 

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