Carboxylic Acids

Carboxylic acids are a homologous series of compounds. Each member differs from the next by one -CH2 molecule in the molecular formulae. All carboxylic acids share the same chemical properties, but there is a gradual variation in their physical properties. For example:

  • Boiling points – Increase as their carbon chain length increases
  • Viscosity – Increase as their carbon chain length increases

One easy way to identify a carboxylic acid is through the ‘-oic acid’ ending in the name. The functional group responsible for the chemical behaviour of carboxylic acids is the carboxyl group, represented as ‘-COOH’.

The general formula for carboxylic acids is:

In terms of the carboxylic acid structure – their molecular formula, structural formula and ball-and-stick model can be seen below:

The table below shows the molecular formula, structural formula and ball-and-stick model for the first four carboxylic acids.

Carboxylic AcidNo. of Carbon AtomsFormulaStructural FormulaStick + Ball Diagram
Methanoic acid1HCOOHThis image has an empty alt attribute; its file name is image-65.pngThis image has an empty alt attribute; its file name is image-55.png
Ethanoic acid2CH3COOHThis image has an empty alt attribute; its file name is image-67.pngThis image has an empty alt attribute; its file name is image-56.png
Propanoic acid3C2H5COOHThis image has an empty alt attribute; its file name is image-68.pngThis image has an empty alt attribute; its file name is image-57.png
Butanoic acid4C3H7COOHThis image has an empty alt attribute; its file name is image-69.pngThis image has an empty alt attribute; its file name is image-59.png