Butan-1-ol is an alcohol that can be converted into 1-bromobutane, a halogenoalkane. Describe the differences in the functional groups of alcohols and halogenoalkanes, and explain how the properties of 1-bromobutane differ from those of butan-1-ol in terms of their ability to dissolve in water and their boiling points.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Butan-1-ol (C₄H₉OH) can be converted into 1-bromobutane (C₄H₉Br) by replacing the hydroxyl group with a bromine atom.
Model answer (5 marks)
Alcohols contain a hydroxyl (–OH) functional group.
Halogenoalkanes contain a halogen atom (here Br) as the functional group, replacing the –OH.
1‑Bromobutane is less soluble in water than butan‑1‑ol.
The –OH group in butan‑1‑ol can form hydrogen bonds with water molecules, giving it greater solubility.
1‑Bromobutane has a higher boiling point than butan‑1‑ol because the larger Br atom gives stronger van der Waals forces.
Halogenoalkanes contain a halogen atom (here Br) as the functional group, replacing the –OH.
1‑Bromobutane is less soluble in water than butan‑1‑ol.
The –OH group in butan‑1‑ol can form hydrogen bonds with water molecules, giving it greater solubility.
1‑Bromobutane has a higher boiling point than butan‑1‑ol because the larger Br atom gives stronger van der Waals forces.
Examiner tips
- Use the exact terms – hydroxyl, halogen, hydrogen bonding, van der Waals. Show the comparison of solubility and boiling point clearly. Keep the answer concise and to the point.
Common mistakes
- Confusing the functional groups (e.g. writing –Br as a hydroxyl). Saying the boiling point is lower for 1‑bromobutane. Forgetting to mention hydrogen bonding as the reason for higher solubility.
Mark scheme (5 marks)
- Alcohols contain a hydroxyl (–OH) functional group
- Halogenoalkanes contain a halogen atom (in this case bromine / –Br) as the functional group, replacing the –OH
- 1-Bromobutane is less soluble in water than butan-1-ol (or: butan-1-ol dissolves more readily in water)
- The –OH group in butan-1-ol can form hydrogen bonds with water molecules, which is why it is more soluble
- 1-Bromobutane has a higher boiling point than butan-1-ol OR butan-1-ol has a lower boiling point than 1-bromobutane because 1-bromobutane has stronger intermolecular (van der Waals) forces due to the larger bromine atom / greater relative formula mass
Key terms in this question
functional group · halogenoalkane · boiling point
Related
- All Eduqas A-Level Chemistry revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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