PSLE Science Chemistry Topics 1 — Questions and Answers
Question 1: Which of the following is an example of a chemical change?
- Ice melting into water
- Wood burning to produce ash and smoke (Correct answer)
- Salt dissolving in water
- Glass breaking into small pieces
Correct answer: Wood burning to produce ash and smoke
Burning wood produces ash and smoke — entirely new substances are formed, which is the defining feature of a chemical change.
Question 2: What term describes the process when water vapour cools and turns back into liquid water?
- Evaporation
- Condensation (Correct answer)
- Sublimation
- Melting
Correct answer: Condensation
Condensation is the process where water vapour loses heat energy and changes back into liquid water.
Question 3: Which state of matter has both a definite shape and a definite volume?
- Gas
- Liquid
- Solid (Correct answer)
- Mixture
Correct answer: Solid
Solids have tightly packed particles that give them a fixed shape and volume that does not change with the container.
Question 4: Which of the following is NOT a physical change?
- Cutting paper into pieces
- Iron rusting when exposed to water (Correct answer)
- Dissolving sugar in water
- Ice melting into liquid water
Correct answer: Iron rusting when exposed to water
Iron rusting is a chemical change because a new substance — iron oxide (rust) — is formed.
Question 5: When a solid changes directly into a gas without passing through the liquid state, this process is called:
- Evaporation
- Condensation
- Sublimation (Correct answer)
- Freezing
Correct answer: Sublimation
Sublimation is when a solid turns directly into a gas — dry ice (solid carbon dioxide) is a classic example.
Question 6: Which statement best describes particles in a liquid?
- Particles are far apart and move freely in all directions
- Particles are tightly packed and vibrate in fixed positions
- Particles are close together but can flow and move past each other (Correct answer)
- Particles have no movement at all
Correct answer: Particles are close together but can flow and move past each other
In a liquid, particles are close together but have enough energy to flow and move past one another, giving liquids a definite volume but no fixed shape.
Question 7: Heating water in a pot until it boils and produces steam is an example of:
- A chemical change, because a new substance is formed
- A physical change, because the water molecules are unchanged (Correct answer)
- A chemical change, because heat is involved
- A physical change, because colour changes
Correct answer: A physical change, because the water molecules are unchanged
Boiling water is a physical change — steam is still made of water molecules, just in a gaseous state, and can be condensed back to liquid water.
PSLE Science Chemistry Topics 1
Which of the following is an example of a chemical change?