Propan-1-ol is an alcohol that can be used as a fuel and as a solvent. Describe the chemical structure of propan-1-ol, including the functional group present, and explain why propan-1-ol is classified as an alcohol rather than a halogenoalkane.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Propan-1-ol has the molecular formula C₃H₇OH and is a colourless liquid at room temperature.
Model answer (5 marks)
Propan‑1‑ol has the formula C₃H₇OH. Its structure is CH₃CH₂CH₂OH – a straight‑chain alkane of three carbons with a hydroxyl (–OH) group attached to the terminal carbon.
The –OH group is bonded to a carbon atom in the chain, giving the compound the characteristic functional group of alcohols.
Because it contains a hydroxyl group, propan‑1‑ol is classified as an alcohol. A halogenoalkane would have a halogen atom (F, Cl, Br or I) replacing a hydrogen on the carbon chain, which propan‑1‑ol lacks. Therefore it cannot be a halogenoalkane.
The –OH group is bonded to a carbon atom in the chain, giving the compound the characteristic functional group of alcohols.
Because it contains a hydroxyl group, propan‑1‑ol is classified as an alcohol. A halogenoalkane would have a halogen atom (F, Cl, Br or I) replacing a hydrogen on the carbon chain, which propan‑1‑ol lacks. Therefore it cannot be a halogenoalkane.
Examiner tips
- Write the full structural formula to show the –OH group clearly.
- Mention that the –OH is bonded to a carbon, not a halogen.
- Explain that a halogenoalkane requires a halogen atom, which is absent.
- Keep the answer concise – 5 marks are enough for a short description and explanation.
Common mistakes
- Confusing the –OH group with a halogen atom; students sometimes write a halogen instead of –OH.
- Omitting the fact that the –OH is bonded to a carbon in the chain.
- Using vague terms like ‘oxygen’ instead of the specific –OH functional group.
Mark scheme (5 marks)
- Propan-1-ol contains a hydroxyl (–OH) functional group
- The hydroxyl group is bonded to a carbon atom in the chain
- Propan-1-ol is classified as an alcohol because it contains the hydroxyl (–OH) functional group
- A halogenoalkane contains a halogen atom (F, Cl, Br or I) in place of a hydrogen atom, which propan-1-ol does not have
- Therefore propan-1-ol cannot be a halogenoalkane because its functional group is –OH not a halogen atom
Key terms in this question
alcohol · halogenoalkane · functional group
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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