Two organic compounds — one with the structure CH₃CH₂OH and another with the structure CH₃CH₂CH₂CH₂OH — both belong to the same class of compounds. Despite having different carbon chain lengths, a chemist predicts their chemical properties will be very similar, but expects their boiling points to differ. Justify both parts of the chemist's prediction.
Generated by claude-sonnet-4-6 · 2026-06-26 01:10 · grounding rag
Model Answer
Both CH₃CH₂OH (ethanol) and CH₃CH₂CH₂CH₂OH (butan-1-ol) belong to the homologous series of alcohols — they share the same functional group (–OH). Since chemical properties are determined solely by the functional group, both compounds show very similar chemical reactions (e.g., reaction with sodium, oxidation).
However, their boiling points differ because, in a homologous series, boiling point increases with increasing molecular mass. Butan-1-ol has a higher molecular mass (74 u) than ethanol (46 u), so it has a higher boiling point.
Source: Carbon and its Compounds, Section 4.2.4 — Homologous Series
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Explanation
- Part 1 (similar chemical properties): Examiners want the key phrase: "functional group determines chemical properties, regardless of chain length." Name the functional group (–OH) and state it's a homologous series.
- Part 2 (different boiling points): The textbook explicitly states "melting and boiling points increase with increasing molecular mass" in a homologous series. Mentioning the actual molecular masses (46 u vs 74 u) adds precision and earns full marks.
- Don't write more than this — padding loses time without gaining marks.