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NCERT Solutions Curiosity Chapter 9 Filtering muddy water through a filter paper — Activity 9.4: Let us experiment

Book page 171 Updated on2026-09-05

Q1.
Try to fold the filter paper yourself and make a cone as shown in Fig. 9.10.
Answer

How to fold it — four steps, exactly as in Fig. 9.10:

  1. Start with a round filter paper lying flat.
  2. One fold — fold it exactly in half. You now have a half-circle.
  3. Two folds — fold the half-circle in half again. You now have a quarter-circle.
  4. Cone — open the quarter out so that three layers lie on one side and one layer on the other. It opens into a cone that sits neatly inside the funnel.
Why a cone and not a flat disc: the cone matches the shape of the funnel, so the paper touches the glass all round and there is no gap along the edge. If there were a gap, the muddy water would run past the paper instead of through it, and nothing would be filtered.
Tip: Wet the folded cone with a little clean water before pouring. The damp paper sticks to the funnel and stays in place while you pour.
Q2.
What do you observe? Do the mud particles pass through the filter paper?
Answer

No, the mud particles do not pass through. They are held back on the filter paper. The water that trickles out of the funnel into the conical flask is clear.

On the filter paper → mud …………… this is the residue
In the conical flask → clear water …… this is the filtrate
Muddy water Filter paper Residue (mud) stays on the paper Funnel Conical flask Filtrate (clear water collected) Stand
Filtration: the filter paper acts as a sieve with extremely fine pores. Water molecules go through; the larger mud particles cannot, and are left on the paper as residue.
Why it works: a filter paper is full of very fine pores. Anything smaller than a pore passes; anything larger is stopped. Mud particles, though invisible to the eye, are far bigger than these pores — so they are trapped and the water goes through.
Did you know? Other materials work as filters too — cotton, charcoal and sand are all used in water filters. Which one you choose depends on the size of the particles you want to remove. Charcoal also takes away bad smell and colour.
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