Methanol and butanol are both members of the alcohols homologous series. Describe TWO chemical properties that methanol and butanol share, and for each property, name the type of reaction or the product(s) formed.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Alcohols are organic compounds containing the functional group –OH. The first four members of the homologous series are methanol, ethanol, propanol and butanol.
Model answer (4 marks)
Both alcohols:
1. Undergo complete combustion in oxygen:
– Reaction: 2C_nH_{2n+1}OH + (3n+1)O_2 → 2nCO_2 + 2H_2O
– Products: carbon dioxide and water.
2. Can be oxidised to carboxylic acids:
– Reaction: C_nH_{2n+1}OH + K_2Cr_2O_7 + 4H_2SO_4 → C_nH_{2n-1}O_2 + Cr_2(SO_4)_3 + 4KHSO_4 + 3H_2O
– Product: methanoic acid (from methanol) or butanoic acid (from butanol).
1. Undergo complete combustion in oxygen:
– Reaction: 2C_nH_{2n+1}OH + (3n+1)O_2 → 2nCO_2 + 2H_2O
– Products: carbon dioxide and water.
2. Can be oxidised to carboxylic acids:
– Reaction: C_nH_{2n+1}OH + K_2Cr_2O_7 + 4H_2SO_4 → C_nH_{2n-1}O_2 + Cr_2(SO_4)_3 + 4KHSO_4 + 3H_2O
– Product: methanoic acid (from methanol) or butanoic acid (from butanol).
Examiner tips
- Use the exact reaction type (combustion, oxidation) and list both products for combustion; name the specific acid for oxidation.
- Show the balanced equation or at least the key reactants and products to demonstrate understanding.
Common mistakes
- Writing incomplete combustion (CO instead of CO2); forgetting water as a product.
- Using the wrong acid name (e.g., calling methanoic acid ‘formic acid’ incorrectly).
Mark scheme (4 marks)
- Both alcohols undergo combustion (burn in oxygen) — accept 'complete combustion produces carbon dioxide and water'
- Carbon dioxide AND water named as products of combustion (both required for this mark)
- Both alcohols can be oxidised to carboxylic acids — accept 'by potassium dichromate(VI)' or 'by microbial oxidation'
- Carboxylic acid named as the product of oxidation (or correct specific acid named, e.g. methanoic acid for methanol / butanoic acid for butanol)
Key terms in this question
Related
- All Pearson Edexcel International GCSE Chemistry (4CH1) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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