Solid to vapour, vapour to solid
Sublimation and deposition.
A white lump vanishes
A lump of camphor left in an open dish slowly gets smaller and smells strongly. It never turns into a puddle of liquid.
Where do you think the camphor goes?
What this lesson covers
The idea
Sublimation is the change of a solid directly into vapour on heating below its melting point, and deposition the direct change of vapour to solid on cooling; so a solid that sublimes separates from one that does not.
A white lump vanishes
A lump of camphor left in an open dish slowly gets smaller and smells strongly. It never turns into a puddle of liquid.
Where do you think the camphor goes?
- It turns straight into vapour in the air
- It melts into a puddle first
- It turns into sand
Heat the dish
A teacher heats a dish of camphor and sand gently. Add a cool plate and watch.
Sublimation and deposition
Sublimation is the change of a solid directly into vapour on heating (below its melting point), without passing through the liquid state. Deposition is the change of vapour directly into solid on cooling. So a solid that sublimes can be separated from one that does not.
Camphor sublimes on heating; sand does not. So camphor separates from sand.
Dry ice (solid carbon dioxide), used for storing ice cream, also sublimes.
Notes
Sublimation: solid straight to vapour on heating. Deposition: vapour straight to solid on cooling. A solid that sublimes separates from one that does not (camphor and sand).
Check yourself
Sublimation is a change…
The vapour of camphor cools on a plate and becomes solid again, without becoming a liquid. This is called…
Why does heating a mixture of camphor and sand separate them?
Which of these also sublimes?
- from liquid to vapour. That is boiling or evaporation.
- from vapour to liquid. That is condensation.
- from solid directly to vapour — correct. Yes.
- deposition — correct. Yes.
- sublimation. Sublimation is solid to vapour.
- melting. Melting is solid to liquid.
- Sand sublimes and camphor does not. It is camphor that sublimes.
- Both melt and pour apart. Neither is poured as a liquid here.
- Camphor sublimes and sand does not — correct. Yes.
- Sand. Sand does not sublime on heating.
- Dry ice (solid carbon dioxide) — correct. Yes.
- Common salt in water. That is a solution, not a solid subliming.