Methanol, ethanol, propanol and butanol are the first four members of a homologous series of alcohols. Alcohols can be oxidised to form carboxylic acids. Describe the relationship between alcohols and carboxylic acids, including the functional groups involved, the names of the carboxylic acids formed from methanol and ethanol, and the typical acidic properties shown by carboxylic acids.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A student is investigating organic compounds in the laboratory. She notices that when certain alcohols are oxidised, they produce compounds with a sharp, pungent smell and acidic properties.
Model answer (5 marks)
Alcohols contain the –OH functional group.
Carboxylic acids contain the –COOH functional group.
Methanol is oxidised to methanoic acid (formic acid).
Ethanol is oxidised to ethanoic acid (acetic acid).
Carboxylic acids are acidic – they react with carbonates to give CO₂, with metals to give H₂, and have a pH below 7.
Carboxylic acids contain the –COOH functional group.
Methanol is oxidised to methanoic acid (formic acid).
Ethanol is oxidised to ethanoic acid (acetic acid).
Carboxylic acids are acidic – they react with carbonates to give CO₂, with metals to give H₂, and have a pH below 7.
Examiner tips
- Use the exact functional group names –OH and –COOH. Mention the specific acids formed from methanol and ethanol. Show the typical acidic reactions (carbonate, metal, pH).
Common mistakes
- Writing ‘methanol to formic acid’ without the systematic name ‘methanoic acid’. Forgetting to state the –COOH functional group. Confusing the reaction with metals as producing H₂ instead of H₂ gas.”
Mark scheme (5 marks)
- Alcohols contain the functional group –OH
- Carboxylic acids contain the functional group –COOH
- Methanol is oxidised to form methanoic acid
- Ethanol is oxidised to form ethanoic acid
- Carboxylic acids show typical acidic properties, such as reacting with carbonates to produce carbon dioxide / reacting with metals to produce hydrogen / having a pH below 7
Key terms in this question
alcohols · carboxylic acids · functional group · oxidised · homologous series
Related
- All OCR A-Level Chemistry A (H432) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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