Std 8 Chem Ch-5 Pollution of Air and Water

Pollution of Air and Water


1. Fill in the blanks.
a.  Soot is a carbon-containing air pollutant.
b. Vehicular emissions contain carbon monoxide  which is an air pollutant.
c. In winters, smoke and fog combine to form smog.
d. Purified water which is fit for drinking is known as potable water.
e. Dissolved impurities present in water can be removed by reverse osmosis(RO).

2. Mark ‘true or false’ against the following statements.
a. Chlorofluorocarbons deplete the ozone layer. True
b. Carbon dioxide is the main cause of global warming. True
c. Hot water cannot be considered as a water pollutant. False
d. Polluted water can alter the quality of soil. True
e. Chlorination is a physical method of purification of water. False

3. Match the following terms in column I with those in column II.
Column I  Column II
1.Microorganisms a. Present in the smoke emitted by vehicles
2. Sulphur dioxide b. A physical water pollutant
3. Tiny particulate matter c. Do not pollute air but pollute water to a large extent
4. Plastics d. An air pollutant emitted by thermal power plants

Ans : 1. –  c , 2. – d , 3. – a , 4. – b

4. What is marble cancer?
Ans. – Pollutant that deposits on the white marble of the Taj Mahal result in the yellowing of the marble. This ruining of the white marble of the Taj Mahal is known as marble cancer.

5. Give a brief account of the following:

a. Water pollutants
Ans. – Water pollutants are substances that pollute water.There are three types of water pollutants.

  1. Physical pollutants : It includes appreciably large particles,debris and various other physical factors that affect the quality of water. E.g. paper,plastic,sediments etc.
  2. Chemical pollutants : It includes different chemical substances that alter the quality of water and contaminate it. E.g. toxic organic compound, toxic metal such as lead,mercury etc.
  3. Biological pollutants : It includes pathogenic microbes originating from sewage that contaminate water. e.g. microorganism such as protozoa and bacteria.

b. Purification of water
Ans. – Purification of water refers to the removal of the unwanted dissolved impurities and harmful microorganism from water. The commonly employed domestic methods of purification of water to make it suitable for drinking are filtration,boiling and chlorination.

6. Give a brief account of the greenhouse effect with a suitable illustration.
Ans. – Greenhouse effect is the significant rise in the average temperature on Earth due to the trapping of the Sun’s heat by certain gases known as the greenhouse gases. They trap the heat in atmosphere. The major greenhouse gases are water vapour, CO,methane and nitrous oxide. How does green house effect occur?

  1. Radiation from the Sun fall on the Earth.
  2. It passes through the atmosphere and warm the Earth.
  3. Some of the radiations are reflected back into space and some are trapped by greenhouse gases.
  4. Re-emission of the absorbed radiations warms the Earth further.

7. How is acid rain formed?
Ans. – sulphur dioxide and nitrogen dioxide combine with rainwater in the atmosphere and form sulphuric acid and nitric acid respectively. These acids come down with rain. Such kind of rain is called acid rain.

8. How does hot water act as a water pollutant?
Ans. – Hot water elevates the temperature of the concerned water bodies and affects aquatic life forms drastically.Therefore hot water also contributes to water pollution.

9. Differentiate between impure water and potable water.
Ans. – Purified water which is fit for drinking is called potable water.It is free from impurities.The water which contains impurities such as suspended particles,microorganisms etc are called impure water.It is not fit for drinking.

10. Briefly describe the role of modern water purifiers.
Ans. – The modern water purifiers remove toxic chemicals as well as biological pollutants from water.Such purifiers are customised in a manner that they do not remove the essential dissolved minerals and the natural nutritional value of the water is retained.

11. How can trees help reduce air pollution?
Ans. – Trees can help reduce air pollution by absorbing excess carbon dioxide. Thus, trees reduce accumulation of carbon dioxide.

12. Compare and contrast air pollution and water pollution.
Air pollution Water pollution
The contamination of air by undesirable particles and gases is know as air pollution. The contamination of water by physical,chemical or biological pollutants that make it unfit for use is know as water pollution.
Sources : motor vehicles,industries,thermal power plant etc Sources : domestic waste,agricultural waste,industrial dumping etc.
Air pollutants : CO2 , SO2 , CFCs,oxides of nitrogen,dust and soot etc. Water pollutants : paper,plastic,lead,mercury,protozoa,bacteria etc.
It causes respiratory problem,asthma,lung diseases,mental disorders etc. It causes typhoid,cholera,jaundice,diarrhoea,cancer etc. It also affects aquatic life.
Acid rain,global warming,depletion of ozone layer are major effects of air pollution. Contamination of most of the river like Ganga, Yamuna,Narmada Tapi are effects of water pollution.

13. What is the reason behind the formation of a white deposit on bathroom walls?
Ans.When calcium reacts with carbonate a solid substance is formed, that is called lime. This lime is what causes the white deposit on showers and bathroom walls and is commonly known as lime deposit. Hard water is water that has high mineral content (in contrast with “soft water”). Hard water is formed when water percolates through deposits of limestone, chalk or gypsum which are largely made up of calcium and magnesium carbonates, bicarbonates and sulfates. Hard drinking water may have moderate health benefits.

14. How is the greenhouse effect related to global warming?
Ans. – Excess carbon dioxide present in the atmosphere is the main cause of global warming.It traps heat from solar radiations and does not allow the heat to escape into space, thus increasing the average temperature on Earth. Like carbon dioxide,other green house gases also contribute to global warming.thus greenhouse effect is related to global warming.

15. Explain how industries affect the quality of water present in water bodies.
Ans. -various factories,textile mills,oil refineries, etc discharge numerous hazardous substances into water.Hazardous substances dumped by industries include toxic metals,harmful chemicals and toxic oils.

16. Why do you think that camel carts, bicycle rickshaws and battery-operated vehicles are used to reach the Taj Mahal from the parking area?

Ans. – Camel carts, bicycle rickshaws and battery-operated vehicles are used to reach the Taj Mahal from the parking area, because they do not emit any toxic gases and thus not pollute the air. Thus the Taj Mahal will be remain safe from marble cancer and doesn’t result into yellowing the marble.

17. Greenhouse effect is a threat to the Earth, but without this phenomenon the existence of life on Earth would not have been possible. Explain why.
Ans. – If greenhouse effect will increase, temperature of Earth will also increase. If global warming reaches higher levels,it can melt the ice in polar regions.It can result in submerging of low-lying areas.This effect also affects rainfall patterns,agriculture,flora and fauna.So it is threat to the Earth.But naturally occurring greenhouse  gases warm the Earth by about 330C, which is required for life to be sustained.Thus we can say that the existence of life on Earth would not have been possible.

18. Do you think that the introduction of “The Delhi Metro Rail’ in Delhi has helped reduce the air pollution in the city? If yes, explain how.
Ans. -The Delhi Metro rail runs on electric power. So, they don’t emit any pollutant substance. Thus, it has helped reduce the air pollution in the city.

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