Page 245 - Chemistry ICSE Class IX
P. 245
Chemistry Practicals 233
Results
From the analysis, it is found that the water in the waterbody (pond, river/lake) near our locality is polluted
with:
y Detergent/soap
y Organic matter
y Soluble salts and metal ions
y Suspended particles
y Acids
This water sample is not usable for humans and animals.
Note: The dissolved oxygen (DO) in water can be easily and quickly estimated by using a DO analyser. The
DO analysers are available commercially in various models.
VIVA VOCE
1. What are the characteristics of drinking (or potable) water?
Ans. Drinking water should be colourless, odourless and free from any suspended impurities, harmful germs, large quantity of
salts, and any harmful pathogens.
2. What are the characteristics of polluted water?
Ans. Polluted water has one or more of the following characteristics:
Foul smell
Bad taste
Oily or greasy scum on the surface of water
Excessive growth of algae and weeds in the water
3. The pH of an industrial effluent is 3.5. What do you conclude from it?
Ans. The industrial effluent is quite acidic.
4. A sample of sewage water smells like rotten eggs. Give reason.
Ans. It is due to the formation of H S due to the decomposition of sulphur-containing organic compounds under oxygen-
2
deficient conditions.
5. Name two oxygen-demanding pollutants in water.
Ans. The oxygen-demanding pollutants in water are:
Organic matter
Plant nutrients – Nitrates and Phosphates
6. Which type of metals in water are toxic and harmful to human body?
Ans. Heavy metals like Cd, Hg, Pb, Zn etc. are toxic and harmful to human body.
7. What causes thermal pollution in water?
Ans. Hot industrial effluents, when discharged directly into a waterbody, cause thermal pollution.
8. What is meant by biological treatment of domestic sewage?
Ans. The biological treatment of domestic sewage includes:
The aerobic bacterial decomposition of organic matter into CO and H O.
2 2
The anaerobic bacterial break down of complex organic molecules into lower acids and alcohol which are then
oxidised to CO and CH by methane bacteria.
2 4
