Science (086) — AI-generated practice question

Micelle: A micelle is a cluster of soap molecules in water where the hydrophobic (hydrocarbon) tails are directed towards the interior and the hydrophilic (ionic) ends face outwards towards water.

Cleaning action:
Soap molecules have two ends — a hydrophilic ionic end that interacts with water, and a hydrophobic carbon-chain end that interacts with oil/grease. When soap is added to oily clothes in water, the hydrophobic tails of soap molecules surround the oily dirt, while the ionic ends face outward into water. This forms a micelle with dirt trapped at its centre. The micelles remain suspended as a colloid (emulsion) and are rinsed away with water, thus cleaning the clothes.

Source: Chapter 4, Section 4.5 Soaps and Detergents

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• 1 mark for defining micelle correctly (cluster, hydrophobic inward, hydrophilic outward).
• 2 marks for explaining the cleaning mechanism: dual nature of soap → surrounds oily dirt → micelle formation → dirt washed away.
• Examiners expect the terms hydrophilic, hydrophobic, ionic end, hydrocarbon tail, and emulsion/colloid to appear.
• A labelled diagram of micelle formation (if drawn correctly) can substitute for some description, but always write the key steps in words too.