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NCERT Solutions Curiosity Chapter 9 Heating salt solution in a china dish — Activity 9.3: Let us investigate

Book page 169 Updated on2026-09-05

Q1.
What do you observe? What is left in the china dish? Did you get the salt back?
Answer

On heating, the solution first boils. Steam rises from the dish and the liquid level keeps falling. When all the water has boiled away, a layer of dry white salt is left sticking to the china dish.

Yes, the salt is recovered — you can feel it with your fingers once the dish has cooled.

Salt solution heated
→ water boils away as vapour
→ white solid salt remains in the china dish
Why filtration would not have worked here: in a solution the salt is broken up so finely that it passes through the tiniest pores along with the water — you cannot see it and you cannot strain it out. The only way to separate a dissolved solid is to send the liquid away as vapour, that is, by evaporation.
Caution: Never bend over a hot china dish or touch it straight after heating. Let the teacher demonstrate, and allow the dish to cool before touching the salt.
Q2.
Is there any method through which I can get back both salt and water? Observe the figure. Does it answer the question? Can you name the process involved?
Answer

Yes. In Activity 9.3 the salt was saved but the water was lost into the air. To keep both, catch the vapour and cool it back into liquid.

The picture shows exactly that — steam from the kettle strikes a cool plate held above it, and clear water drips from the plate into a glass.

Heat the salt solution → water becomes vapour ……… evaporation
Cool the vapour on a cold surface → vapour becomes liquid ……… condensation
Result: pure water in the glass + salt left in the vessel

Name of the process: the pair of steps together is evaporation followed by condensation. When it is done in the laboratory with proper apparatus, it is called distillation.

Why the drops are pure water: only the water turns to vapour. The salt stays behind in the hot vessel. So whatever condenses on the cool plate is water without the salt — this is how distilled water is made.
Check it yourself: Hold a cold steel plate a little above the steam of a pan of boiling water for a few seconds. Water droplets form on the underside. That is condensation, the reverse of evaporation — and it is also how rain is formed.
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