Ethanol can be converted into chloroethane (a halogenoalkane) by replacing the hydroxyl group with a chlorine atom. Describe what happens to the functional group during this conversion and explain why chloroethane is classified as a halogenoalkane rather than an alcohol.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Ethanol has the molecular formula C₂H₅OH. Chloroethane has the molecular formula C₂H₅Cl.
Model answer (5 marks)
Ethanol contains a hydroxyl (–OH) functional group.
During the conversion the –OH group is removed and replaced by a chlorine atom.
The chlorine atom takes the place of the –OH group, giving a C–Cl bond.
Chloroethane is classified as a halogenoalkane because it has a halogen atom bonded to a carbon chain.
It is not an alcohol because it no longer contains a hydroxyl (–OH) group.
During the conversion the –OH group is removed and replaced by a chlorine atom.
The chlorine atom takes the place of the –OH group, giving a C–Cl bond.
Chloroethane is classified as a halogenoalkane because it has a halogen atom bonded to a carbon chain.
It is not an alcohol because it no longer contains a hydroxyl (–OH) group.
Examiner tips
- Use the exact terms – hydroxyl group, halogen atom, halogenoalkane, alcohol.
- Show the sequence: –OH removed → Cl added.
- Explain classification based on presence/absence of –OH.
- Keep answer concise and to the point.
Common mistakes
- Saying the –OH group is ‘moved’ instead of ‘removed and replaced’. Confusing a halogenoalkane with an alkane or alcohol. Omitting the reason why it is not an alcohol (lack of –OH).
Mark scheme (5 marks)
- Ethanol contains a hydroxyl (–OH) functional group
- The hydroxyl (–OH) group is removed/replaced during the conversion
- A halogen atom (chlorine) is introduced / takes the place of the –OH group
- Chloroethane is classified as a halogenoalkane because it contains a halogen atom bonded to a carbon chain / alkane chain
- Chloroethane is not an alcohol because it does not contain a hydroxyl (–OH) group
Key terms in this question
halogenoalkane · alcohol · hydroxyl group · 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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