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Water — CHEMISTRY STD 7 — Question

ICSE BoardEnglish MediumSTD 7CHEMISTRYWater4 Marks
Question
Mention the ways by which
a. suspended impurities can be removed from drinking water.
b. germs present in drinking water are destroyed.
✓

Answer

(a) The suspended impurities from water is removed by the following methods,
  1. Sedimentation – Water is fed into the sedimentation tanks. The large solid particles are allowed to settle down as sediment.
  2. Loading – In the loading tank, water is treated with potash alum to increase the rate of sedimentation. Fine suspended particles become heavy after mixing with potash alum and settle down at the bottom of the tank.
  3. Filteration – Following loading, water is passed through Alteration tank. The filteration tank has filter beds that contain layers of fine sand, gravel and charcoal. The filter beds remove all suspended impurities from the water.
(b) Germs present in drinking water can be destroyed by –
  1. Chlorination – The filtered water is treated by bleaching powder which releases chlorine when dissolved in water and destroys harmful microorganisms in it. The addition of chlorine to drinking water is called chlorination.
  2. UV radiation – These destroy harmful microorganisms from water. It does not affect the taste and odour of the water.
  3. Ozonization – Ozone gas is also used to disinfect drinking water. It does not affect the taste and odour of water.

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