Year 7 Science · Unit 2 · Lesson 13
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Learning Goals
True or false? Fix the false ones
Circle T or F. If a statement is false, correct it on the line.
1. Ice melts when its particles vibrate hard enough to break out of their fixed positions.
Correct it:
2. Boiling water makes a new substance, because steam looks different from liquid water.
Correct it:
3. Water vapour condenses on a cold window because its particles gain energy.
Correct it:
4. Dry ice turns straight from a solid into a gas without becoming a liquid.
Correct it:
5. A steel rail gets longer on a hot day because its particles move faster and spread further apart.
Correct it:
1. What is diffusion? Give one everyday example.
Cause and effect: a hot-air balloon
Fill each empty box. Each box is caused by the one before it, and row 2 carries on from the end of row 1.
Match each job to a separation technique
Write the letter of the best technique in the middle column. Each letter is used once. The techniques are not in the same order as the jobs.
| Job | Letter | Technique (property it uses) |
|---|---|---|
| Getting salt back from salt water | A. Filtration (particle size) | |
| Separating the dyes in black ink | B. Evaporation (boiling point of the solvent) | |
| Removing tea leaves from a pot of tea | C. Distillation (different boiling points) | |
| Separating alcohol from water | D. Chromatography (attraction to the paper) |
Read the data: tin, lead and solder
Scenario: melting three metals
Solder is used to join electrical wires. This solder is made by melting tin and lead together and letting them cool; other solders use a different recipe, with more or less tin. A lab heated a sample of each metal slowly and recorded when it began to melt and when it had fully melted.
| Metal | Begins to melt (°C) | Fully melted (°C) |
|---|---|---|
| Tin (Sn) | 232 | 232 |
| Lead (Pb) | 327 | 327 |
| Solder (60% tin, 40% lead) | about 183 | about 190 |
Source: published values, rounded.
2. Use the matter family tree to place tin, lead and solder. Give one reason for each.
3. Why did the lab record two temperatures for each metal, not just one? Use Table 1 in your answer.
4. Sam says: “Solder melts at a lower temperature than tin or lead, so melting them together must have made a new compound.” Evaluate Sam’s claim.
5. A camper on a beach has only a bucket of muddy seawater. Describe how to get clean drinking water from it, using two separation techniques in the right order. For each technique, name the property it uses. Then explain why the salt left behind at the end is still salt.
True or false
1. True. 2. False: boiling is a change of state; the particles are still H₂O. 3. False: the particles lose energy and slow down. 4. True. 5. True: the particles themselves do not grow; they just take up more room.
Question 1
Particles spreading from high to low concentration, without stirring (1). Example: food colouring spreading in still water, or a smell across a room (1). [2 marks]
Cause and effect: a hot-air balloon
Box 1: air particles gain energy and move faster (1). Box 2: they push further apart; the air expands (1). [2 marks]
Match each job to a separation technique
Getting salt back from salt water → B; Separating the dyes in black ink → D; Removing tea leaves from a pot of tea → A; Separating alcohol from water → C.
Question 2
Tin: element, one type of atom (Sn) (1). Lead: element, one type of atom (Pb) (1). Solder: mixture of tin and lead, not bonded, recipe can vary (1). [3 marks]
Question 3
A pure substance melts at one temperature: tin and lead read the same twice (1). This solder melts over a range, 183 to 190 °C, so it is a mixture (1). [2 marks]
Question 4
Wrong: a new melting temperature alone does not prove a compound (1). Solder’s recipe varies and it melts over a range: a mixture, not a new substance (1). [2 marks]
Question 5
Marking guide: 1 filtration, particle size; 1 filter first, leaving only dissolved salt; 1 distillation, different boiling points; 1 water boils off, condenses and is collected; 1 particles only separated, not changed; 1 so salt keeps its properties. [6 marks]
Model answer: First filter it: mud grains are too big to pass through the paper, so only salt water gets through. Then distil it: water boils at a far lower temperature than salt, so only the water boils off; cool the steam so it condenses and collect it, leaving the salt. The salt and water particles were only separated, not changed, so the salt keeps its own properties.
Common error: choosing evaporation; the water escapes into the air.