Generated by claude-sonnet-4-6 · 2026-06-15 06:47 · grounding rag
Model Answer
(a) Compounds (1) CH₃CH₂CHO (propanal) and (3) CH₃CH₂CH₂CHO (butanal) belong to the same homologous series — aldehydes — as both contain the –CHO functional group and differ by one –CH₂– unit.
(b)
(i) Melting point increases with increasing molecular mass in a homologous series.
(ii) Solubility (in water) decreases with increasing molecular mass in a homologous series.
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Explanation
- (a) Homologous series members must have the same functional group and differ by –CH₂–. Compound (2) is a ketone (–CO–) and compound (4) is an alcohol (–OH), so they don't fit. Only (1) and (3) are both aldehydes.
- (b) This is a standard textbook property of homologous series. Examiners expect both parts answered clearly. Larger molecules have stronger intermolecular forces (higher m.p.) but are less polar, reducing water solubility.