Primary 5 · Science · Cycles: Boiling, Melting & Freezing
Cycles: Boiling, Melting & Freezing questions for Primary 5 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.
- Reading a freezing curve
- What stays the same
- Evaporation against boiling
- Why the temperature holds
- Speeding up a change
- Reasoning about impurities
- Naming a temperature
- Naming a change
- Applying the ideas
Same picture as the question above.
| Dish of water | Temperature (°C) | Bubbles inside the liquid? | Water level falling? |
|---|---|---|---|
| A | 30 | ✗ | ✓ |
| B | 70 | ✗ | ✓ |
| C | 100 | ✓ | ✓ |
| Liquid | Freezing point (°C) |
|---|---|
| pure water | 0 |
| lightly salty water | -2 |
| very salty water | -9 |
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.
In the graph above, what is happening during the flat part of the line?
Answer: The water is freezing into ice.
The line holds at 0 °C while the water turns to ice. The freezer goes on taking heat out, but that heat is used to change the state rather than to lower the temperature.
According to the graph, at what temperature did the water freeze?
Answer: 0 °C
The flat part of the line, where the water turns to ice, sits at 0 °C.
An ice cube melts completely inside a sealed jar. Which two statements are correct?
Answer: A and B only
A change of state changes how the particles are arranged, not what they are or how many. The jar holds the same water and the same mass, now liquid.
Based on the table above, what distinguishes boiling from evaporation?
Answer: Boiling happens at one fixed temperature and makes bubbles throughout the liquid.
All three dishes lost water, so evaporation happens at any temperature. Only the dish at 100 °C bubbled, which is what boiling is.
Ice at 0 °C is heated steadily. Why does its temperature not rise until all of it has melted?
Answer: The heat going in is used to change the ice into water rather than to warm it.
Changing state takes energy. While any ice remains, the heat arriving does that job, so the temperature stays at 0 °C until the last of it has melted.
Which two of these would make a puddle of water freeze faster?
Answer: A and B only
A colder night takes heat out faster, and a shallower puddle has less water to cool. Salt and insulation both work against freezing.
Based on the table above, why does the sea rarely freeze even when a nearby lake does?
Answer: Sea water is salty, so it has to be much colder before it freezes.
Fresh water freezes at 0 °C but very salty water not until -9 °C. A night cold enough to freeze the lake often leaves the sea liquid.
This is the name for the temperature at which a solid turns into a liquid. It is called the ______ point.
Answer: melting
The temperature at which a solid becomes a liquid is its melting point.
Wet clothes on a line become dry without ever reaching 100 °C. Which change of state has taken place?
Answer: evaporation
Water leaving the clothes as vapour below boiling point is evaporation.
A bottle of water left completely full in a freezer cracks. Why?
Answer: Water expands as it freezes, and the ice needs more room than the bottle has.
Water is unusual: it takes up more space as ice than as liquid. A full sealed bottle leaves the ice nowhere to expand into, so it forces the bottle apart.