Introduction
This PSLE Science question focuses on evaporation, a key concept tested frequently in both Booklet A and Booklet B.
Hand sanitiser contains alcohol, which evaporates much faster than water.
The teacher explains how heat from the hand speeds up evaporation, causing the hand to dry quickly.
The Question
Afiq sprayed some hand sanitiser on his hand.
State why Afiq’s hand became dry very quickly.
Step-by-Step Explanation (Following Teacher’s Working)
1. Hand sanitiser contains alcohol
Alcohol has a lower boiling point and evaporates much faster than water.
2. The sanitiser absorbs heat from Afiq’s hand
The teacher writes:
- “Sanitiser will gain heat”
- “and become a vapour”
This matches the scientific explanation:
When evaporation happens, particles absorb heat energy from the surroundings (the hand).
3. The alcohol evaporates quickly
Because the particles gain heat, the sanitiser changes from liquid → vapour rapidly.
4. As a result, the hand becomes dry
Since the liquid sanitiser evaporates quickly, no liquid remains on the hand.
✅ Final Answer
The sanitiser gains heat from Afiq’s hand and evaporates quickly, causing his hand to become dry.
Key Concepts
| Concept | Why It Matters |
| Evaporation | Explains how liquids become vapour |
| Heat Transfer | Liquid needs heat to evaporate |
| Alcohol vs. Water | Alcohol evaporates faster |
| Cooling Effect | Hand may feel cold as heat is lost |
Tips for Students
✔ Remember: Evaporation requires heat.
✔ Think about where the heat comes from — usually the surroundings (skin, air).
✔ Alcohol evaporates faster than water because of its lower boiling point.
✔ Always link your answer: gains heat → evaporates → dries quickly.
For Parents
This is a classic PSLE question assessing understanding of phase changes.
Kids who can explain evaporation clearly will do well in both MCQs and long-answer questions.
Mastering these fundamentals builds confidence for more complex heat and matter questions.