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Detergents and polymers — KCSE Chemistry

KCSE Chemistry · 38 practice questions · 3 syllabus objectives

2 easy23 medium13 hard

What You'll Learn

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

Distinguish between soapy and soapless detergents and explain their cleansing action

Describe natural and synthetic polymers and their uses

Explain addition and condensation polymerisation reactions

Sample Questions

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1
easySHORT ANSWER2 marks

Which of the following represents a soapless detergent? A: R—C₆H₄—SO₃⁻Na⁺ B: R—COO⁻K⁺ (a) Identify the soapless detergent and explain your answer. (b) Give the chemical name for the detergent identified.

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Part (a) — 2 marks
A is the soapless detergent — it has a sulphonate group (—SO₃⁻) attached to a benzene ring. B is a soap (carboxylate salt) (1 mk)
2
easySHORT ANSWER4 marks

The following structures represent different cleaning agents: (i) CH₃(CH₂)₁₆COO⁻Na⁺ (ii) CH₃(CH₂)₁₁C₆H₄SO₃⁻Na⁺ (a) Identify which is a soap and which is a soapless detergent. Explain your choice. (b) State the general formula for a soap. (c) Explain the difference between a hard soap and a soft soap.

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Part (a) — 4 marks
(i) is a soap — it is the sodium salt of a long-chain carboxylic (fatty) acid, identified by the —COO⁻Na⁺ (carboxylate) group (1 mk)
(ii) is a soapless detergent — it is the sodium salt of an alkylbenzene sulphonic acid, identified by the —SO₃⁻Na⁺ (sulphonate) group (1 mk)
3
mediumSHORT ANSWER6 marks

Describe the differences between natural and synthetic detergents and explain their respective advantages. (6 marks)

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Part (a) — 3 marks
Natural detergents are derived from natural sources like plants or animal fats (1 mk)
Synthetic detergents are chemically manufactured and can be tailored for specific functions (1 mk)
Synthetic detergents often perform better in hard water compared to natural detergents (1 mk)
Part (b) — 3 marks
Natural detergents are biodegradable and less harmful to the environment (1 mk)
Synthetic detergents can be formulated to target specific stains and have enhanced cleaning properties (1 mk)
Synthetic detergents can be produced in bulk, making them more affordable (1 mk)
4

Describe how synthetic polymers are produced and discuss one significant application of one type. (6 marks)

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