Page 223 - New Medley 4 Semester 2 PDF (Merged)

Boiling

Filtration of dirty water removes only the insoluble impurities from water. The water still

may have germs. To make the water drinkable and germ-free, we boil water for about
15 minutes. Boiling kills the germs present in water.

Chlorination

Chemicals such as chlorine, potassium permanganate, etc. are also used to kill

germs present in water. Adding chlorine to water is called chlorination. For
purifying water by chlorination, chlorine tablets are also used. One small chlorine

tablet is enough to make about 20 litres of water germ-free.

2 • Understanding

Fill in the blanks.
1. The level of water under the ground is called .

2. The is cyclic movement of water in the earth’s atmosphere.

3. The are formed by the gathering of water droplets in the air.

4. The mixing of harmful substances in water is termed as .

5. kills the germs present in water.

AT ONE GO

m The continuous change of water into water vapour and again into liquid water is called water cycle.

m Precipitation occurs in the form of rain, snow, fog, hail, dew and frost.
m Water becomes impure due to the addition of soluble and insoluble impurities.
m Water can be purified by sedimentation and decantation and filtration.

m Water can be made germ-free by boiling or using chemicals like chlorine and potassium permanganate.

REMEMBER THESE TERMS

Condense : To change a gaseous form into its liquid form
Fertilisers : Chemicals used for good growth of plants

Pesticides : Chemicals used to kill insects, rats, weeds, etc.
Purification : Cleaning

Germ-free : Without germs

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