Soap micelle in water
Hydrophobic tails inward; hydrophilic heads outward — dirt trapped inside.
Step 1 — Study the figure
Cover the label key on the image, name each numbered part, then check the explanations below.
Step 2 — Diagram details for students
What this diagram shows
A soap micelle explains cleansing action: hydrophobic tails trap oil while hydrophilic heads stay in water. The greasy dirt becomes suspended and can be washed away. Hard water reduces soap efficiency because calcium and magnesium form scum.
Numbered parts — mark & remember
Match each number on the figure with the meaning below. Say the function aloud once.
1 Hydrophilic head
The head of a soap molecule loves water and is ionic/polar. In a micelle, heads point outward into the surrounding water. This keeps the whole cluster dispersed in the washing water.
2 Hydrophobic tail
The long hydrocarbon tail hates water and prefers oil or grease. Tails point inward toward the oily dirt. This opposite behaviour of head and tail is the key to soap action.
3 Oil / dirt core
Oily dirt collects in the centre of the micelle among the tails. Once trapped, dirt no longer sticks strongly to cloth. Rinsing then carries the micelles away.
4 Water outside
Water surrounds the micelle and interacts with the heads. The suspension looks cloudy sometimes but can be washed off. Detergents work on a similar idea and often perform better in hard water than ordinary soap.
How to read this figure
- Heads outside, tails inside — never reverse this in diagrams.
- Micelle = cleansing unit that emulsifies grease in water.
- Link hard water scum to Ca²⁺/Mg²⁺ with soap.
Redraw for board marks
- Draw a circle of heads on the outside.
- Draw tails pointing inward to a shaded oil core.
- Label head, tail, oil, and water clearly.
Board answer tip: Draw a micelle with labelled head/tail/oil/water and explain how grease is washed away.
Exam tips — don’t lose marks
- Soap cleans by micelle formation, not by “eating dirt”.
- Hard water + soap → scum; detergents are better in hard water.
- Mention emulsification of grease for 2–3 mark answers.