Year 7 Science · Unit 2 · Lesson 9
Foundation Worksheet
Learning Goals
Fill the gap
Choose the correct word from the word bank. Each word is used at most once. Two words are not needed: cross them out.
When salt dissolves in water, the salt is the and the water is the . Together they form a . Because the solvent is water, we say the solution is . A solution with very little salt dissolved in a large amount of water is called . If the water is holding the most salt it can at that temperature, the solution is .
True or false? Fix the false ones
Circle T or F. If a statement is false, correct it on the line.
1. The solvent is the substance that gets dissolved in a solution.
Correct it:
2. Adding more water to a cordial makes it more dilute.
Correct it:
3. In sweet tea, the water is the solvent and the sugar is the solute.
Correct it:
4. When sugar dissolves in water, the sugar particles turn into water particles.
Correct it:
5. In a saturated solution, extra solute will no longer dissolve at that temperature.
Correct it:
1. Ella makes a sweet drink by adding one teaspoon of sugar to 200 mL of water. Name the solute in her drink, and name the solvent.
2. Complete the table. The first row is done for you.
| Solution | Solute (what dissolves) | Solvent (what it dissolves in) |
|---|---|---|
| Salt water | salt | water |
| Soda water (fizzy water) | ||
| Brass (copper with a little zinc) | ||
| Air |
3. Is Ella’s drink from Question 1 dilute or concentrated? Explain how you know.
Read the data
Scenario: how much salt will dissolve?
Noah puts 100 mL of water at 20 °C into each of four glasses. He adds a different amount of salt to each one and stirs for five minutes. At 20 °C, 100 mL of water can dissolve at most 36 g of salt.
| Glass | Salt added (g) | What Noah saw |
|---|---|---|
| A | 2 | All dissolved; clear liquid |
| B | 20 | All dissolved; clear liquid |
| C | 36 | All dissolved; one more pinch of salt stayed on the bottom |
| D | 50 | 14 g of salt still sitting on the bottom |
Source: sample class results for this worksheet.
4. Which glass holds the most dilute solution? Which two glasses are saturated? Give the evidence from Table 1 for each of those two.
5. Work out the mass of salt in solution in glass D. Why would adding another spoonful to glass D leave its concentration unchanged?
6. Sugar seems to vanish when it is stirred into a glass of water. Draw two particle pictures, one before and one after the sugar dissolves (use ○ for water particles and ■ for sugar particles). Then explain where the sugar has gone, using the words solute, solvent and particles.
Fill the gap
solute; solvent; solution; aqueous; dilute; saturated. Not needed: concentrated, compound.
True or false
1. False: the solvent does the dissolving; the solute is what gets dissolved. 2. True. 3. True. 4. False: the sugar particles stay as sugar particles; they spread out between the water particles. 5. True.
Question 1
Solute: sugar (1). Solvent: water (1). [2 marks]
Question 2
Soda water: carbon dioxide gas; water (1). Brass: zinc; copper (1). Air: oxygen and the other gases; nitrogen (1). [3 marks: 1 per row, both cells correct]
Question 3
Dilute (1): only a small amount of solute (one teaspoon of sugar) is dissolved in a large amount of solvent (200 mL of water) (1). [2 marks]
Read the data
4. Most dilute: A (1). Saturated: C, because the extra pinch did not dissolve (1); D, because undissolved salt sits on the bottom (1). [3 marks]
5. 36 g (50 g added − 14 g left on the bottom) (1). The water is already holding the most salt it can at 20 °C, so any extra salt just sits undissolved on the bottom (1). [2 marks]
Question 6
Marking guide: 1 before: sugar particles packed in a grain, water particles around it; 1 after: the same number of sugar particles, spread between the water particles; 1 water (solvent) particles bump the grain and knock sugar (solute) particles loose; 1 the freed particles slip into the gaps between water particles; 1 the sugar is still there: taste it, or boil off the water to get the crystals back. [5 marks]
Model answer: The sugar has not vanished. Water (solvent) particles bump into the grain and knock sugar (solute) particles loose one at a time. They slip into the gaps between the water particles and spread through the glass, too spread out to see. Each is still a sugar particle: the water tastes sweet, and boiling the water away brings the crystals back.
Common error: drawing fewer sugar particles after dissolving, as if some had disappeared.