Year 7 Science · Unit 2 · Lesson 6
Foundation Worksheet
Learning Goals
True or false? Fix the false ones
Circle T or F. If a statement is false, correct it on the line.
1. Filtration works because sand grains are too large to pass through the tiny pores in filter paper.
Correct it:
2. Filtration can remove dissolved salt from salt water.
Correct it:
3. In evaporation, the water leaves as vapour and the salt stays behind in the basin.
Correct it:
4. Evaporation destroys the salt, so it disappears along with the water.
Correct it:
5. Separation methods are chemical changes, because they turn the parts of a mixture into new substances.
Correct it:
Match each term to its meaning
Write the letter of the correct meaning next to each term. Each letter is used once.
| Term | Letter | Meaning |
|---|---|---|
| Filtration | A. Able to dissolve in a liquid. | |
| Evaporation | B. The liquid that passes through the filter paper. | |
| Residue | C. Separating an insoluble solid from a liquid by pouring it through filter paper. | |
| Filtrate | D. Heating a solution so the liquid leaves as vapour and the dissolved solid stays behind. | |
| Soluble | E. The solid left trapped on the filter paper. |
1. Why can’t filtration separate salt from salt water? Name the method you should use instead, and say why it works.
Odd one out
Judge each mixture by the method you would use to separate it: a magnet, filtration or evaporation. In each row, circle the mixture that needs a different method from the other three, and name the method it needs.
| Mixtures | Odd one out and the method it needs |
|---|---|
| iron filings in sand · steel paper clips in rice · sand in water · steel nails in sawdust | |
| chalk dust in water · salt dissolved in water · soil in water · sand in water | |
| sugar dissolved in water · seawater · muddy water · salt dissolved in water |
Read the data
Scenario: filtering four mixtures
A class pours four mixtures through filter paper. They note what is left on the paper and what the filtrate looks like. Then they evaporate a few drops of each filtrate on a watch glass.
| Mixture | Left on the filter paper | What the filtrate looks like | Left after evaporating a few drops of filtrate |
|---|---|---|---|
| A: sand and water | wet sand | clear, colourless | nothing |
| B: salt and water | nothing | clear, colourless | white crystals |
| C: chalk dust and water | white paste | clear, colourless | nothing |
| D: muddy water with red food colouring | brown mud | clear, red | a red stain |
Source: sample class results.
2. Which two mixtures contained a solid that had dissolved? Give the evidence from Table 1.
3. The filtrate from mixture D is clear but still red. Explain why the filter paper caught the mud but not the colour.
4. Kai has a beaker of salt, sand and water. Explain, step by step, how he can get back dry sand and dry salt. Say why each step works, and why the steps must be done in that order.
True or false
1. True. 2. False: dissolved salt particles pass through the pores with the water. 3. True. 4. False: the salt stays in the basin; only the water leaves. 5. False: they are physical changes; the parts are unchanged.
Match each term to its meaning
Filtration → C; Evaporation → D; Residue → E; Filtrate → B; Soluble → A.
Question 1
Dissolved salt particles are far smaller than the pores, so they pass through (1). Evaporation (1): water boils at 100 °C but salt melts only at about 800 °C, so heat drives off the water and leaves the salt (1). [3 marks]
Odd one out
Row 1: sand in water, filtration (the others use a magnet) (1). Row 2: salt dissolved in water, evaporation (the others use filtration) (1). Row 3: muddy water, filtration (the others hold a dissolved solid, so evaporation) (1). [3 marks]
Question 2
B and D (1): their filtrates left a solid after evaporating (white crystals, red stain), so a dissolved solid passed through the paper (1). [2 marks]
Question 3
The mud had not dissolved; its bits are too big for the pores, so they stayed on the paper (1). The food colouring had dissolved into particles smaller than the pores, so it went through with the water (1). [2 marks]
Question 4
Marking guide: 1 filter the mixture first; 1 the sand is the residue, as its grains are too big for the pores (rinse and dry it); 1 the salt has dissolved, so it passes through with the water into the filtrate; 1 evaporate the filtrate gently so the water leaves and the salt stays; 1 order: evaporating first would leave the salt and sand mixed together as one dry solid. [5 marks]
Model answer: First Kai filters the mixture. The sand grains are too big for the pores, so sand is the residue; he rinses and dries it. The salt has dissolved, so it passes through in the filtrate. Then he heats the filtrate gently in an evaporating basin; the water leaves as vapour and dry salt is left. If he evaporated first, the salt and sand would be left mixed together.
Common error: calling the filtrate from salt water pure water; it is still salty.