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Carboxylic acids

The form a . Like all homologous series, the carboxylic acids:

  • have the same
  • differ by CH2 in from neighbouring
  • show a gradual variation in , such as their
  • have similar

Functional group

The in the carboxylic acids is the group, 鈥揅OOH.

Molecular structure of carboxyl

It is responsible for the typical reactions of carboxylic acids, which are weak . Vinegar is a dilute solution of ethanoic acid.

General formula

The general formula for the carboxylic acids is CnH2n+1COOH (where n is the number of carbon atoms in the molecule, minus 1).

Remember that the O atoms are not joined to each other:

Worked example

Decanoic acid is a carboxylic acid. Its contain 10 carbon . Predict the molecular formula of decanoic acid and explain your answer.

The formula will be C9H19COOH. This is because n = (10 鈥 1) = 9. So, 2n+ 1 = (2 脳 9) = 18 + 1 = 19.

Question

Hexanoic acid is a carboxylic acid. Its molecules contain 6 carbon atoms. Predict the molecular formula of hexanoic acid.

Structures

The table shows four carboxylic acids, their molecular, displayed and structural formulae.

Table displaying carboxylic acids and their molecular, displayed and structural formulae.

Acid properties

The carboxylic acids have the typical properties of acids. For example, they:

  • in water to form with values lower than 7
  • react with to form a and hydrogen
  • react with to form a salt and water
  • react with carbonates to form a salt, water and carbon dioxide

These properties are due to the 鈥揅OOH functional group.