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š¬ Think about it
Heat camphor and it disappears into vapour without ever melting into a liquid. Mix it with sand, and only the camphor vanishes. That is how we separate them. Let us explore sublimation.
What is sublimation?
- It is when a solid changes directly to vapour on heating, without becoming liquid.
- On cooling, the vapour turns back to solid; this is called deposition.
- Camphor sublimes but sand does not, so they separate.
Sublimation and Deposition
Solid camphor + sand
↓
Heat (sublimation)
Camphor turns straight to vapour; sand stays.
↓
Cool (deposition)
Vapour turns back to solid camphor.
↓
Camphor separated from sand
In this Activity, we will separate camphor from sand by subliming the camphor and collecting it on a funnel.
Procedure
1. Put a spatula of crushed camphor and sand mixture in a clean, dry china dish on a tripod stand with wire gauze.
2. Take a clean, dry glass funnel and plug its nozzle with cotton.
3. Keep the funnel inverted on the china dish (Fig. 5.17).
4. Light the burner under the wire gauze.
5. Heat the china dish gently for a few minutes.
6. Observe the inner wall of the funnel for solid deposits.
7. White solid camphor deposits form on the funnel wall, while sand stays in the dish.
2. Take a clean, dry glass funnel and plug its nozzle with cotton.
3. Keep the funnel inverted on the china dish (Fig. 5.17).
4. Light the burner under the wire gauze.
5. Heat the china dish gently for a few minutes.
6. Observe the inner wall of the funnel for solid deposits.
7. White solid camphor deposits form on the funnel wall, while sand stays in the dish.
You can also use another sublimable substance like naphthalene instead of camphor.
ā Summary
- Heat camphor and sand.
- Camphor turns to vapour.
- It deposits on the funnel.
- Sand stays in the dish.
What is an alloy?
- Metals do not dissolve in each other at room temperature.
- When melted and mixed, they form a homogeneous mixture called an alloy.
- An alloy is a mixture of two or more metals, or a metal and a non-metal.
- Physical methods cannot separate an alloy's components.
Example:
Brass is about 80% copper and 20% zinc; bronze is about 80% copper and 20% tin.
Important Points
- Sublimation is a solid turning straight to vapour; deposition is the reverse.
- It separates a sublimable solid (camphor) from a non-sublimable one (sand).
- An alloy is a homogeneous mixture of metals that cannot be separated physically.
š§¬ Pause and Ponder
-
Why do immiscible liquids form two separate layers in a separating funnel?
Because they do not mix and have different densities, so the lighter liquid floats above the heavier one. -
Is sublimation different from evaporation? Justify.
Yes — in sublimation a solid changes directly to vapour without becoming liquid, while in evaporation a liquid changes to vapour at its surface.
ā Test Yourself
-
What is sublimation?
View Answer
A solid changing directly to vapour without becoming a liquid. -
What is deposition?
View Answer
Vapour changing back to solid without becoming a liquid. -
What is an alloy?
View Answer
A homogeneous mixture of two or more metals, or a metal and a non-metal.
Important Definitions
- Sublimation — a solid changing directly to vapour (below its melting point) without becoming liquid.
- Deposition — vapour changing back to solid without becoming liquid.
- Alloy — a homogeneous mixture of two or more metals, or a metal and a non-metal.
š NCERT Question 11 — You are given a
A mixture of sand, common salt and naphthalene — write the correct sequence of separation techniques.
View Answer →
