Science (086) — AI-generated practice question

A homologous series is a group of compounds with the same functional group, differing by a –CH₂– unit each time.

Different boiling points: As molecular mass increases in a homologous series, physical properties (such as boiling point) show a gradation. Pentanol (C₅H₁₁OH, mol. mass = 88 u) has a much higher molecular mass than methanol (CH₃OH, mol. mass = 32 u), so its boiling point is significantly higher.

Same chemical behaviour with sodium: Chemical properties in a homologous series are determined solely by the functional group. Both pentanol and methanol contain the –OH (hydroxyl) functional group, so they react identically with sodium metal.

Source: Chapter 4, Section 4.2.4 – Homologous Series

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• Examiners expect two separate, clearly labelled observations explained using the two key properties of a homologous series.
• Physical properties (boiling point, melting point, solubility) show gradation with increasing molecular mass — this is the principle for the first part.
• Chemical properties depend only on the functional group, not on chain length — this explains the second part.
• Mention actual molecular masses or the –CH₂– difference to show you understand the series; this earns the third mark.