Pupil sheet · Crystallisation
Can any more dissolve? — questions
Name ______________________ Date ____________
Try every question before you use a nudge. Write in full sentences where you are asked to explain.
1. explain
At a steady temperature, an added crystal of the same solute dissolves completely after stirring. Was the solution saturated before you added it? Explain using the observation.
Circle one answer.
- Saturated
- Unsaturated
What does the disappearing crystal tell you?
Nudge (only if you are stuck): Could the solution dissolve more of that solute at this temperature?
2. explain
Choose the statements that distinguish concentrated from saturated. Explain why looking at colour cannot establish saturation.
Tick every correct statement.
- Concentrated describes relative solute amount.
- Concentrated always means no more can dissolve.
- Saturation depends on the specified temperature.
- Any coloured solution is saturated.
Why is colour alone insufficient?
Nudge (only if you are stuck): Which word describes how much solute is present? Which describes a dissolving limit?
3. explain
A clear blue solution has no visible grains. Does that establish that it's unsaturated? Describe a test that would give useful evidence.
Your conclusion
Evidence or test and reasoning
Nudge (only if you are stuck): How could you test whether more of the same solute can dissolve, while keeping temperature steady?
4. state
Fill the gaps to distinguish relative concentration from a dissolving limit. Include the condition that must be stated for saturation.
Relatively much dissolved solute
At the dissolving limit
Condition that must be specified
Nudge (only if you are stuck): Can a solution contain relatively much solute and still dissolve more? What condition sets its limit?
5. explain
Solid X dissolves up to 4 g in 10 g water at 20°C. In both clear samples, all added solid has dissolved. Use the table to compare concentration and saturation. Explain what their identical clear appearance can and cannot establish.
| Sample | Water | Dissolved X | Temperature |
|---|---|---|---|
| A | 10 g | 2 g | 20°C |
| B | 10 g | 4 g | 20°C |
Relative concentration and evidence
Saturation at 20°C and evidence
What appearance and an added-solute test tell you
Nudge (only if you are stuck): Each sample has the same water amount. How does its dissolved mass compare with the 4 g limit?