Name a suitable technique for the separation of the components from a mixture of calcium sulphate and camphor.

Exercises · 8.27

Q. Name a suitable technique for the separation of the components from a mixture of calcium sulphate and camphor.

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Concept understanding — Separation Techniques

Separation Techniques: The Intuition

Imagine you're making chai. You boil tea leaves in water, then pour the liquid through a strainer. The strainer catches the leaves; the tea flows through. You just performed a separation technique — you took a mixture (tea leaves + water) and isolated one component (the liquid tea) from the other (the solid leaves).

Every separation technique answers one question: How do I pull apart things that are mixed together, using their differences?

The key insight: You cannot separate things that are identical. Separation works only because the components of a mixture differ in at least one physical or chemical property — size, density, boiling point, solubility, magnetic behaviour, or something else.

Note

Separation techniques are physical processes. They do not change the chemical identity of the substances. The tea leaves remain tea leaves; the water remains water. No chemical reaction occurs.

The Precise Statement

Separation techniques are methods used to isolate individual components from a mixture by exploiting differences in their physical or chemical properties. The goal is to obtain one or more pure substances from a mixture, without altering the chemical nature of the components.

The Core Idea in One Sentence

Important

Every separation technique works because the components of the mixture differ in at least one measurable property. The method you choose depends entirely on which property differs.

A Quick Map of Common Separation Techniques

Here is how the choice of technique follows from the property difference:

Property Difference	Technique	Example
Particle size	Sieving, Filtration	Separating stones from sand; tea leaves from water
Density	Centrifugation, Decantation, Sedimentation	Separating cream from milk; mud from water
Boiling point	Distillation	Separating alcohol from water; crude oil into fractions
Solubility	Evaporation, Crystallisation	Obtaining salt from seawater
Magnetic property	Magnetic separation	Separating iron filings from sulphur powder
Volatility	Sublimation	Separating camphor from sand
Attraction to a stationary phase	Chromatography	Separating pigments in ink or plant leaves

How to Think About Any Separation Problem

When you see a mixture and need to decide how to separate it, ask yourself:

What are the components? (List them.)
What property is different between them? (Size? Density? Boiling point? Solubility? Magnetism?)
Which technique exploits that difference? (Match the property to the method above.)

That three-step chain — mixture → property difference → technique — is the entire logic of separation.

A Concrete Walkthrough

Mixture: Sand and iron filings.

Components: Sand (silicon dioxide) and iron (metal).
Property difference: Iron is magnetic; sand is not.
Technique: Magnetic separation. Pass a magnet over the mixture. Iron filings stick to the magnet; sand is left behind.

Mixture: Salt dissolved in water.

Components: Salt (sodium chloride) and water.
Property difference: Water boils at $100^\circ\text{C}$ and evaporates; salt does not boil or evaporate — it remains as a solid.
Technique: Evaporation (or distillation, if you also want to collect the water). Heat the solution. Water turns to vapour and leaves; salt crystals remain in the dish.

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The key idea is to exploit the large difference in volatility between the two solids — camphor sublimes readily while calcium sulphate does not — so sublimation cleanly separates them, leaving calcium sulphate behind and collecting camphor as a sublimate.

Why sublimation works here

Separation techniques rely on differences in physical properties. For a mixture of two solids, you look for a property that is drastically different — solubility, density, magnetic behaviour, or, as in this case, volatility.

Calcium sulphate ( $\text{CaSO}_4$ ) is an inorganic salt with a high melting point (around $1450\,^\circ\text{C}$ ) and essentially no vapour pressure at ordinary temperatures. It does not sublime. Camphor ( $\text{C}_{10}\text{H}_{16}\text{O}$ ), on the other hand, is an organic compound that sublimes readily — it passes directly from solid to vapour at room temperature and pressure, without melting. This difference is the basis of the separation.

Tip

Camphor’s sublimation is so pronounced that you can often smell it from a distance — the vapour pressure is high enough at $25\,^\circ\text{C}$ to make it detectable. That’s a rare property among common solids.

Step-by-step procedure

Place the mixture in a shallow dish — a china dish or a watch glass works well. Spread it out so that camphor vapour can escape easily from the entire surface.
Cover the dish with a funnel — an inverted glass funnel is ideal. Plug the stem of the funnel loosely with cotton wool. This prevents camphor vapour from escaping while still allowing air to vent.
Heat the dish gently — use a low flame or a sand bath. The temperature should be just enough to vaporise camphor (it sublimes around $175\,^\circ\text{C}$ at atmospheric pressure) but well below the decomposition temperature of calcium sulphate.
Watch for the sublimate — camphor vapour rises, hits the cool inner surface of the funnel, and deposits as a white, crystalline solid. This is the sublimate. Calcium sulphate remains in the dish as a residue.
Scrape off the camphor — once the heating is done and the apparatus has cooled, carefully collect the camphor crystals from the funnel wall. The residue in the dish is pure calcium sulphate. …

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Q.Name a suitable technique for the separation of the components from a mixture of calcium sulphate and camphor.

Why sublimation works here

Step-by-step procedure

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