Amines are a group of organic compounds that contain nitrogen. Describe the structure of an amine and explain why amines are classified as bases.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Methylamine, CH₃NH₂, is the simplest amine. It dissolves in water to produce an alkaline solution.
Model answer (5 marks)
An amine contains a nitrogen atom bonded to one or more carbon or hydrogen atoms – the –NH₂ (amino) functional group. The nitrogen has a lone pair of electrons.
The lone pair can accept a proton (H⁺). When an amine accepts a proton it becomes an ammonium ion, so the amine acts as a proton‑accepting base.
In water the amine accepts a proton from H₃O⁺, forming NH₃⁺ and leaving OH⁻ in solution. The OH⁻ ions raise the pH above 7, giving an alkaline solution.
The lone pair can accept a proton (H⁺). When an amine accepts a proton it becomes an ammonium ion, so the amine acts as a proton‑accepting base.
In water the amine accepts a proton from H₃O⁺, forming NH₃⁺ and leaving OH⁻ in solution. The OH⁻ ions raise the pH above 7, giving an alkaline solution.
Examiner tips
- Use the term ‘amino group’ or ‘–NH₂’ to show structure; mention the lone pair; explain proton acceptance; link to OH⁻ formation and alkaline pH.
- Ensure you state both structure and base behaviour – two separate points – and give the water reaction for the third.
- Use UK spelling (e.g. ‘hydroxide’).
Common mistakes
- Confusing amines with amides or missing the lone pair; writing that amines donate protons instead of accept; not mentioning the alkaline effect in water.
Mark scheme (5 marks)
- An amine contains a nitrogen atom bonded to one or more carbon/hydrogen atoms (or: contains the –NH₂ functional group / amino group)
- The nitrogen atom in an amine has a lone pair of electrons
- The lone pair can accept / receive a proton (H⁺)
- Because amines accept protons / H⁺ they act as bases (proton acceptors)
- When an amine dissolves in water it produces hydroxide ions (OH⁻), making the solution alkaline / pH above 7
Key terms in this question
Related
- All WJEC A-Level Chemistry (Wales) revision notes →
- How to answer a "Describe and Explain" question →
- Decode the mark scheme abbreviations →
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