# Explain how the functional groups present in an amino acid molecule account for its ability to act as a buffer in aqueous solution.

> IB DP Chemistry Standard Level (2023 syllabus) — S3.2 Functional groups: classification of organic compounds · Explain · 4 marks

> Amino acids are the monomers of proteins. Glycine, the simplest amino acid, has the molecular formula C₂H₅NO₂ and contains two distinct functional groups.

## Mark scheme (4 marks)

1. Amino acids contain an amino group (–NH₂) and a carboxyl group (–COOH).
2. The carboxyl group can donate a proton (act as an acid), neutralising added base: –COOH → –COO⁻ + H⁺.
3. The amino group can accept a proton (act as a base), neutralising added acid: –NH₂ + H⁺ → –NH₃⁺.
4. Because the molecule can respond to both increases and decreases in H⁺ concentration, it resists changes in pH, acting as a buffer.

## Key terms

- [buffer](https://www.gradenine.co.uk/glossary/buffer)

## Related

- [Revision notes for IB DP Chemistry Standard Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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