Primary 4 · Science · Cycles: Boiling, Melting & Freezing
Cycles: Boiling, Melting & Freezing questions for Primary 4 Science
10 questions to work through online, 2 of them written out the way the paper asks. Answer and you get the working straight away, then a score at the end. No sign-up, and you can retake it as often as you like.
- Naming a change of state
- Reading a heating graph
- Melting and boiling points
- What speeds up melting
- Evaporation against boiling
- Reading results
- What does not change
- Naming a temperature
- Applying the ideas
| Substance | Melting point (°C) | Boiling point (°C) |
|---|---|---|
| W | 0 | 100 |
| X | -39 | 357 |
| Y | 801 | 1465 |
| Z | -218 | -183 |
Answers and explanations for all 10 questions
Every answer with the reasoning behind it. Worth reading after you have tried the set — or on its own, if you are a parent marking it.
Water turning into ice is called
Answer: freezing
A liquid becoming a solid is freezing, so water turning into ice is freezing.
In the graph above, why does the line stay flat for a while partway up?
Answer: The ice is melting, and the temperature does not rise until it has all melted.
While a solid is melting, the heat going in is used to change the state rather than to raise the temperature. Only once all the ice has melted does the temperature climb again.
At what temperature does pure water freeze?
Answer: 0 °C
Pure water freezes at 0 °C, which is the same temperature at which ice melts.
Which two of these would make an ice cube melt faster?
Answer: A and B only
Melting is faster when heat reaches the ice more quickly. A warm room means more heat flowing in, and crushing gives more surface for that heat to enter through.
A puddle on a playground dries up on a sunny day, though the water never reaches 100 °C. What has happened?
Answer: The water evaporated, which happens below boiling point too.
Evaporation turns liquid into gas at the surface, and it happens at any temperature — just faster when it is warm and windy. Boiling is the special case at 100 °C.
Based on the table above, which substance is a gas at room temperature, about 30 °C?
Answer: Z
A substance is a gas once it is above its boiling point. Z boils at -183 °C, which is well below 30 °C, so at room temperature it is already a gas.
An ice cube melts completely in a sealed jar. Which two statements are correct?
Answer: A and B only
Melting changes the state, not the substance and not the amount. The jar holds the same water, the same mass, now in liquid form.
Water droplets appear on the outside of a cold glass on a hot day. The water vapour in the air has turned into liquid. What is this change called?
Answer: condensation
A gas turning into a liquid is condensation.
Pure water boils at one particular temperature at sea level. What is that temperature in degrees Celsius? (Answer with a number.)
Answer: 100
Pure water boils at 100 degrees Celsius at sea level.
Why is salt spread on icy roads in cold countries?
Answer: It makes the ice melt at a lower temperature than usual.
Adding salt lowers the temperature at which water freezes, so ice that would stay solid at that temperature melts instead.