Class 11 - Chemistry - Environmental Chemistry

Define environmental chemistry.


Environmental chemistry is the branch of science that deals with chemical changes and biochemical

processes occurring in our environment.

 Question 14.2

Explain tropospheric pollution in 100 words.


Tropospheric pollution occurs due to the presence of undesirable substances in air.

Major gaseous pollutants in air are oxides of sulphur, nitrogen, carbon and hydrocarbons.

These are produced as a result of burning of fossil fuels like coal.

These oxides when react with water in the presence of atmospheric oxygen forms harmful substances.

2SO2 + O2 + 2H2O à 2H2SO4

4NO2 + O2 + 2H2O à 4HNO3

This causes acid rain. This causes harm to plants, animals and other objects which comes in direct contact with it.

Particulate pollutants are dust, mist, foam and smog.


Question 14.3

Carbon monoxide gas is more dangerous than carbon dioxide gas. Why?


Carbon monoxide combines with hydrocarbons to form very stable compound called carboxyhaemoglobin.

When the concentration of carboxyhaemoglobin in blood reaches to about 3-4%, oxygen carrying capacity is greatly reduced.

This leads to headache, nervousness and sometimes leads to death.

Carbon dioxide does not combine blood in this way, hence it is less harmful than CO.


Question 14.4

List gases which are responsible for greenhouse effect.


Gases that cause greenhouse effect:

  1. Methane
  2. Carbon dioxide
  3. Nitrous oxide
  4. Water
  5. Ozone


Question 14.5

Statues and monuments in India are affected by acid rain. How?


Statues and monuments are affected by acid rain due to large number of industries and power plants in the nearby areas.

Acid rain contains vapours of sulphuric acid dissolved in it.

Reaction with occurs when acid rain comes in contact with statues and monuments.

CaCO3 + H2SO4 --> CaSO4 + H2O + CO2



Question 14.6

What is smog? How is classical smog different from photochemical smog?


Smog is a combination of smoke and fog. It is a type of air pollution which occurs in many cities.

Classical smog occurs in cool humid climate. It is also called as reducing smog.

Photochemical smog occurs in warm and dry sunny climate.

It has high concentration of oxidizing agents and is also called as oxidizing smog.



Question 14.7

Write down the reactions involved during the formation of photochemical smog.


Photochemical smog is formed due to the reaction of sunlight with nitrogen oxides and hydrocarbons. 

Main components of photochemical smog are formaldehyde, nitric acid, ozone, PAN, acrolein.




Question 14.8

What are the harmful effects of photochemical smog and how can they be controlled?


Harmful effects of photochemical smog:

  1. Ozone and PAN act as eye irritants.
  2. It causes corrosion of metals, stone, building materials, etc.
  3. It leads to cracking of rubber and extensive damage to plants.
  4. It causes headache, chest pain and throat infections in humans.

Controlling photochemical smog:

  1. Use of catalytic converter in automobiles prevents the release of nitrogen dioxide and hydrocarbons to the atmosphere.
  2. Plants like pinus, pyrus can metabolise nitrogen dioxide. Thus, more such trees should be planted.



Question 14.9

What are the reactions involved for ozone layer depletion in the stratosphere?


Reactions involved for ozone layer depletion in the stratosphere:



Question 14.10

What do you mean by ozone hole? What are its consequences?


Ozone hole is the depletion in the blanket of ozone layer in the stratosphere.

Consequences of ozone layer:

  1. UV rays filter into troposphere which leads to ageing of skin, cataract, sunburn, skin cancer.
  2. It can kill phytoplanktons and can damage fish productivity.
  3. As evaporation rate increases from leaves, it can decrease moisture content of the soil.



Question 14.11

What are the major causes of water pollution? Explain.


Causes of water pollution:

  1. Pathogens: Bacteria and many other microbes enter water from domestic sewage and animal excreta.
  2. This can lead to gastrointestinal diseases.
  3. Organic wastes when added to water decompose organic matter and consume dissolved oxygen in water.
  4. When concentration of DO in water decreases below 6 ppm, growth of fish is inhibited.
  5. This breakdown produces chemicals that have foul smell and is harmful to human health.
  6. Chemical pollutants: Pollutants such as cadmium, mercury, etc dissolve in water.
  7. These metals are harmful to humans and other animals. These metals can affect kidney and central nervous system.



Question 14.12

Have you ever observed any water pollution in your area? What measures would you suggest to control it?


Water pollution arises from various human activities such as discharge of wastewater from treatment plants,

run-off from agriculture fields, storm-water discharge, etc. Pollutants from here enter into the water bodies and contaminate water, making it impure.

Measures to control water pollution:

  1. Concentration of these pollutants should be checked regularly.
  2. All the water discharges from factories should be made free from toxic materials.



Question 14.13

What do you mean by Biochemical Oxygen Demand (BOD)?


The amount of oxygen required by bacteria to breakdown the organic matter present in certain volume

of a sample of water is called BOD or biological oxygen demand.



Question 14.14

Do you observe any soil pollution in your neighbourhood? What efforts will you make for controlling the soil pollution?


Major sources of soil pollution are industrial waste and agricultural pollutants.

Controlling soil pollution:

  1. Avoid direct addition of pollutants to the soil.
  2. Waste should be properly treated before discharging into the ground.
  3. Waste should be recycled and allowed to be dumped.



Question 14.15

What are pesticides and herbicides? Explain giving examples.


Pesticides are the chemical compounds used in agriculture to control damage caused by insects, weeds, etc. Example: Aldrin,

Herbicides are chemicals used to control weeds. Example: Triazines.



Question 14.16

What do you mean by green chemistry? How will it help decrease environmental pollution?


Green chemistry is the production process which uses existing knowledge that uses principles of chemistry to create,

develop and implement chemical compounds and products to decrease the amount of harmful substances in the environment.

If the automobile engines have been fitted with catalytic convertors which prevent the release of vapours of HCs

and oxides of nitrogen into acrolein and peroxyacetyl nitrate.



Question 14.17

What would have happened if the greenhouse gases were totally missing in the earth’s atmosphere?


Solar energy radiated back from the earth’s surface is absorbed by the green house gases.

These are present near Earth’s surface and heat up atmosphere and kepp it warm.

There is growth of vegetation which support life and in the absence of this, there is no life.



Question 14.18

A large number of fish are suddenly found floating dead on a lake.

There is no evidence of toxic dumping but you find an abundance of phytoplankton. Suggest a reason for the fish kill.


The amount of DO present in water is limited. Abundance of phytoplanktons causes depletion in dissolved oxygen.

Phytoplanktons are degraded by bacteria present in water. This requires large amount of oxygen.

They consume oxygen which is dissolved in water. BOD level of water drops below 6 ppm, inhibiting growth of fish and causes excessive death of fishes.



Question 14.19

How can domestic waste be used as manure?


Domestic waste consists of biodegradable wastes such as fruit or vegetable peel which can be converted into manure by suitable method.



Question 14.20

For your agricultural field or garden you have developed a compost producing pit.

Discuss the process in the light of bad odour, flies and recycling of wastes for a good produce.


Compost where pit is produced should be covered so that flies cannot make entry into it and bad odour is minimized.

Waste material which is non-biodegradable must be disposed off carefully.

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