Putrescine is a diamine produced when proteins decompose. It has a strong, unpleasant odour. Putrescine contains two amine groups and dissolves readily in water to produce an alkaline solution. Compare the properties of putrescine with those of ammonia, and explain why both compounds produce alkaline solutions when dissolved in water.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Putrescine is a diamine produced when proteins decompose. It has a strong, unpleasant odour. It contains two amine groups and dissolves readily in water to produce an alkaline solution.
Model answer (5 marks)
Both contain nitrogen with a lone pair of electrons.
Both accept a proton from water, forming NH4+ and OH−.
The excess OH− gives an alkaline solution.
Putrescine is an organic diamine, ammonia is an inorganic monamine.
Putrescine has two –NH2 groups and a carbon chain; ammonia has one nitrogen atom and no carbon chain.
Both accept a proton from water, forming NH4+ and OH−.
The excess OH− gives an alkaline solution.
Putrescine is an organic diamine, ammonia is an inorganic monamine.
Putrescine has two –NH2 groups and a carbon chain; ammonia has one nitrogen atom and no carbon chain.
Examiner tips
- Use the command word ‘compare’ – list similarities first, then differences.
- Show the proton‑accepting reaction for each compound.
- Explain that OH− excess gives alkalinity.
- Mention the organic vs inorganic nature and the number of amine groups.
Common mistakes
- Confusing the number of amine groups or omitting the carbon chain in putrescine.
- Failing to state that both produce OH− and thus are alkaline.
- Using vague terms like ‘nitrogenous’ without specifying lone pair or proton acceptance.
Mark scheme (5 marks)
- Both putrescine and ammonia contain nitrogen (with a lone pair of electrons) / both are nitrogen-containing compounds
- Both accept a proton (H⁺) from water / both react with water to produce hydroxide ions (OH⁻)
- This produces an alkaline solution because OH⁻ ions are present in excess
- Putrescine is an amine / organic compound, whereas ammonia is an inorganic compound
- Putrescine has two amine (–NH₂) groups, whereas ammonia has one nitrogen / no carbon chain attached
Key terms in this question
amine · diamine · alkaline · ammonia
Related
- All Eduqas A-Level Chemistry revision notes →
- How to answer a "Compare" question →
- Decode the mark scheme abbreviations →
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