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NCERT Solutions Curiosity Chapter 9 Drops of salt solution on black paper — Activity 9.2: Let us observe and create

Book page 168 Updated on2026-09-05

Q1.
Do you observe some patches on the paper? What do you think is left on the paper? You can feel the presence of salt by touching the paper. Where has the water disappeared?
Answer

Yes — after the drops dry, faint white patches appear on the black paper, exactly where the drops were. What is left there is the salt. It feels slightly rough and gritty when you run a finger over it.

Where the water went: it did not vanish. It evaporated — it changed slowly into water vapour and mixed into the air of the room.

Salt solution on paper
→ water changes to water vapour and goes into the air (evaporation)
→ salt is left behind as a white patch
Why only the water leaves: water turns into vapour easily at ordinary temperatures. Salt does not — it stays as a solid. So when the mixture dries, the solvent goes and the dissolved solid stays. This is precisely how salt is obtained from seawater in the salt pans, only there the “paper” is a huge shallow pit and the “drying” is done by the sun.
Try This: Make your own salt art. Paint a pattern on thick black paper with the salt solution and let it dry in the sun. The dried lines show up in white — the salt has drawn your picture for you.
Q2.
Have you ever observed white patches on the dark coloured clothes you wear during hot summers? How are these patches formed?
Answer

Yes — those whitish rings on a dark shirt, usually under the arms, on the collar and on the back, are made of salt from our own sweat.

Sweat = water + common salt and other substances dissolved in it
In the heat, the water evaporates from the cloth
The salt cannot evaporate, so it stays in the cloth → white patch
Why it shows up in summer and on dark clothes: in hot weather we sweat far more, so more salt is deposited. And white salt against a dark colour is easy to see — on a white shirt the same patch is nearly invisible.
Did you know? This is why we are told to drink nimbu-paani with a pinch of salt, or ORS, on a hot day. Sweating loses the body both water and salt, and both have to be put back.
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