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Reactions of Amino Acids

Chemistry: Cambridge International A Level, topic 3.7.4

Acid and Base Properties of Amino Acids

Amino acids have an acidic carboxylic acid group (-COOH) and a basic amine group (-NH2. They often exist as zwitterions with -COO- and NH3+ groups.

Adding alkali to amino acids 1

Adding alkali to amino acids 1

  • Adding alkali to an amino acid removes an H+ ion from the NH3+ group.
  • The H+ reacts with the alkali (-OH-) to form water (H2O).
  • This leaves the amino acid with an overall negative charge which is located on the carboxylic acid group (-COO-)
Adding alkali to amino acids 2

Adding alkali to amino acids 2

  • As the amino acid now has an overall negative charge, it will attract positive ions in solution.
  • These will often be metal ions (e.g. Na from NaOH).
  • This will lead to the formation of a carboxylate salt group on the amino acid (-COO-Na+)
Adding acid to amino acids

Adding acid to amino acids

  • Adding acid to an amino acid zwitterion adds a H+ ion to the -COO- group to form a -COOH group.
  • The NH3+ remains unchanged.
  • This leaves the amino acid with an overall positive charge.

Test yourself on Reactions of Amino Acids

  • What is the overall charge of an amino acid after it has reacted with an acid?

  • What is the overall charge of an amino acid after it has reacted with an alkali?

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