Alkanes — KCSE Chemistry

KCSE Chemistry · 91 practice questions · 4 syllabus objectives

30 easy30 medium31 hard

What You'll Learn

Key learning outcomes for this topic, aligned to the KNEC KCSE syllabus.

Name and write structural formulae of alkanes with 1–6 carbon atoms using IUPAC nomenclature

Describe combustion and substitution reactions of alkanes with equations

State the physical properties of alkanes and relate them to molecular size and intermolecular forces

Alkanes

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easySHORT ANSWER4 marks

Identify the density of alkanes compared to water. Explain why this property is significant for their behaviour in water. (4 marks)

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Part (a) — 2 marks

Alkanes are less dense than water (1 mk)

Alkanes float on water due to lower density (1 mk)

Part (b) — 2 marks

Alkanes do not mix with water due to density difference (1 mk)

This leads to the formation of separate layers in mixtures (1 mk)

easySHORT ANSWER4 marks

Identify the trend in boiling points of alkanes as the number of carbon atoms increases. Explain the reason for this trend. (4 marks)

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Part (a) — 2 marks

Boiling points increase with an increase in the number of carbon atoms (1 mk)

Larger alkanes have higher boiling points than smaller alkanes (1 mk)

Part (b) — 2 marks

Increased molecular size leads to greater van der Waals forces (1 mk)

Higher energy is required to overcome these intermolecular forces (1 mk)

easySHORT ANSWER3 marks

State the general equation for a substitution reaction of an alkane with chlorine in the presence of ultraviolet light. (3 marks)

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Part (a) — 3 marks

Alkane + Chlorine → Haloalkane + Hydrogen chloride (1 mk)

Indicate that the alkane can be any saturated hydrocarbon (1 mk)

Indicate that the reaction requires ultraviolet light (1 mk)

Name the products formed when butane (C₄H₁₀) undergoes complete combustion in excess oxygen. (2 marks)