More than two parts
A bowl holds chalk powder, salt and camphor (kapoor). One method cannot take out all three.
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Step 1 of 5
- A dry bowl holds chalk powder, salt and camphor.
- Heat gently. Camphor sublimes (turns straight to vapour) and is collected.
- Add water. The salt dissolves.
- Filter. The chalk powder stays on the paper.
- Boil the water away. The salt is left.
The rule
Each part needs its own step. The step uses a property that sets the part apart. Do each step only while its property still works. A later step must not undo an earlier one.
The sublimation set-up heats a dry mixture. So sublimation comes before adding water. Once water is in, camphor and chalk powder stay together. Neither dissolves, so both stay as solids.
| Part | Property | Step |
|---|---|---|
| Camphor | Turns to vapour on heating | Heat gently first |
| Salt | Dissolves in water | Add water, then filter |
| Chalk powder | Does not dissolve | Stays on the paper |
| Salt from the water | Water turns to vapour | Boil the water away |
Camphor is harmful to breathe or swallow. Only a teacher does this, in a well-aired room.