Butane, butene and butanol are organic compounds. State the functional group present in butanol and explain why butane and butanol both belong to different homologous series despite containing the same number of carbon atoms.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
The functional group in butanol is the hydroxyl group (–OH).
Butane and butanol both have four carbon atoms, but they belong to different homologous series because a homologous series is defined by the functional group present. Butane is an alkane, having only C–C and C–H single bonds and no functional group. Butanol is an alcohol, containing the –OH functional group, which places it in the alcohol series. Thus, despite having the same number of carbons, the differing functional groups assign them to separate homologous series.
Butane and butanol both have four carbon atoms, but they belong to different homologous series because a homologous series is defined by the functional group present. Butane is an alkane, having only C–C and C–H single bonds and no functional group. Butanol is an alcohol, containing the –OH functional group, which places it in the alcohol series. Thus, despite having the same number of carbons, the differing functional groups assign them to separate homologous series.
Examiner tips
- Use the exact terms – hydroxyl group, alkane, alcohol; state the definition of a homologous series; explain the role of the functional group; keep the answer concise and to the point.
Common mistakes
- Writing ‘–OH is a functional group’ without specifying it’s the hydroxyl group; confusing the general formula of the series; not mentioning that alkanes have no functional group; including unnecessary details about bonding.
Mark scheme (4 marks)
- The functional group in butanol is the hydroxyl group (–OH)
- A homologous series is a family/series of compounds with the same functional group (and same general formula)
- Butane belongs to the alkane homologous series which contains no functional group / has only C–H and C–C single bonds
- Butanol belongs to the alcohol homologous series because it contains the –OH functional group, which is different from butane's series
Key terms in this question
functional group · homologous series
Related
- All Cambridge International IGCSE Chemistry (0620) revision notes →
- How to answer a "State and Explain" question →
- Decode the mark scheme abbreviations →
More Formulae, functional groups and terminology questions
- A student is studying two organic compounds: ethanol and ethanoic acid. State th…
- Propan-1-ol and propan-2-ol are both members of the alcohol homologous series. E…
- Pentane and pentene are both organic compounds containing five carbon atoms. Sta…
- Describe what is meant by a homologous series and state two characteristics that…