NCERT Solutions for Class 11 Chemistry Chapter 14 Environmental Chemistry: Download Question & Answer PDF

A 14.1 Environmental chemistry is a branch of environmental studies. Environmental studies deal with the sum of all social, economical, biological, physical and chemical interrelations with our surroundings. Environmental chemistry deals with the study of the origin, transport, reactions, effects and fates of chemical species in the environment.

A 14.2 Tropospheric pollution occurs due to the presence of undesirable solid or gaseous particles in the air. The following are the major gaseous and particulate pollutants present in the troposphere:1. Gaseous air pollutants: These are oxides of sulphur, nitrogen and carbon, hydrogen sulphide, hydrocarbons, ozone and other oxidants.2. Particulate pollutants: These are dust, mist, fumes, smoke, smog etc.

A 14.3 Carbon monoxide binds to haemoglobin to form carboxyhaemoglobin, which is about 300 times more stable than the oxygen-haemoglobin complex. In blood, when the concentration of carboxyhaemoglobin reaches about 3–4 per cent, the oxygen carrying capacity of blood is greatly reduced. This oxygen deficiency, results into headache, weak eyesight, nervousness and cardiovascular disorder. This is the reason why people are advised not to smoke. In pregnant women who have the habit of smoking the increased CO level in blood may induce premature birth, spontaneous abortions and deformed babies. On the other hand CO₂ does not combine with haemoglobin and hence is less harmful than CO.

A 14.4 CO₂ is mainly responsible for greenhouse effect. Other greenhouse gases are methane, nitrous oxide, water vapours, CFCs (chlorofluorocarbons) and Ozone.

A 14.5

This is mainly due to the large number of industries and power plants in the nearby areas. Acid rain has vapours of sulphuric acid dissolved in it. When it comes in contact with various statues or monuments, the acid reacts chemically with marble (calcium carbonate).
CaCO₃ + H₂SO₄ → CaSO₄ + H₂O + CO₂

As a result, the monument is being slowly disfigured and the marble is getting discoloured and lustreless.

A 14.6 The word smog is a combination of smoke and fog. It is a type of air pollution that occurs in many cities throughout the world. Classical smog occurs in cool humid climate. It is also called as reducing smog. Whereas photochemical smog (photo means light) occurs in warm and dry sunny climate. It has high concentration of oxidising agents and therefore, it is also called as oxidising smog.

A 14.7 

A 14.8

Harmful effects of photochemical smog: Photochemical smog causes serious health problems. Both ozone and PAN (peroxyacetyl nitrate) act as powerful eye irritants. Ozone and nitric oxide irritate the nose and throat and their high concentration causes headache, chest pain, dryness of the throat, cough and difficulty in breathing. Photochemical smog leads to cracking of rubber and extensive damage to plant life. It also causes corrosion of metals, stones, building materials, rubber and painted surfaces.

Control:

• Control of primary precursors of photochemical smog, such as NO2 and hydrocarbons, the secondary precursors such as ozone and PAN, the photochemical smog will automatically be reduced.
• Use of catalytic converter in automobiles prevents the release of nitrogen oxide and hydrocarbons to the atmosphere.
• Plants like Pinus, juniparus, quercus, pyrus etc. can metabolise nitrogen oxide thus their plantation could help in this matter.

• A 14.9  The reaction can be shown as follows:
• CF₂Cl₂(g) + UV → Cl(g) + CF₂Cl(g)
• Cl(g) + O₃(g) → ClO (g) + O₂(g)
• ClO(g) + O(g) → Cl + O₂(g)

A 14.10 Depletion of ozone layer creates some sort of holes in the blanket of ozone which surrounds us, this is known as ozone hole.

The consequences are:

1. With the depletion of ozone layer, more UV radiation filters into troposphere. UV radiations lead to ageing of skin, cataract, sunburn, skin cancer, killing of many phytoplanktons, damage to fish productivity etc.
2. It has also been reported that plant proteins get easily affected by UV radiations which leads to the harmful mutation of cells.
3. It also increases evaporation of surface water through the stomata of the leaves and decreases the moisture content of the soil.
4. Increase in UV radiations damage paints and fibres, causing them to fade faster.

A 14.11

Major Causes of water pollution are:

• Pathogens: Pathogens include bacteria and other microorganisms that enter water from domestic sewage and animal excreta.
  Human excreta contain bacteria such as Escherichia coli and Streptococcus faecalis, which cause gastrointestinal diseases.
• Organic wastes: Organic wastes when added to water are decomposed by bacteria which consume dissolved oxygen in water. When the concentration of dissolved oxygen of water decreases below 6 ppm, the growth of fish gets inhibited. Breakdown of the organic wastes by anaerobic bacteria produces chemicals that have a foul smell and are harmful to human health.
• Chemical pollutants: Some inorganic chemicals as an industrial wastes dissolve in water like cadmium, mercury nickel etc. These metals are dangerous to humans and other animals. These metals can damage kidneys and central nervous system, liver etc. Petroleum products pollute many sources of water.

A 14.12

Yes, we observed water pollution near our area due to various human activities like toxic discharges from factories and industrial plants, runoff from agricultural fields, domestic wastes etc.

It can be controlled by preventing the toxic chemicals from entering the water bodies. Regular checks on contamination or rivers, lakes or ponds of toxic compounds need to be done. Use of chemical fertilizers should be avoided to prevent the harmful chemicals from entering the ground water.

A 14.13 The amount of oxygen required by bacteria to breakdown the organic matter present in a certain volume of a sample of water is called Biochemical Oxygen Demand (BOD).

A 14.14

The major sources of soil pollution are industrial wastes and agricultural pollutants likes fertilizers and pesticides. Insecticides like DDT are insoluble in water and are absorbed by plant roots. Many pesticides like Aldrin and Dieldrin are toxic and non-biodegradable which can enter the higher trophic levels through food chains, causing metabolic and physiological disorders. Industrial wastes comprise of several toxic metals such as Pb, As, Hg, Cd etc.

For controlling soil pollution, the addition of pollutants to the soil should be avoided. Waste materials should undergo proper treatment and recycling before dumping.

A 14.15 Pesticides are the chemical compounds used to control the damages caused by pests (insects, rodents etc.)
Example: Aldrin, Dieldrin, B.H.C etc.
Herbicides are the chemicals used to control weeds.
Example: Triazines, Sodium chlorate (NaClO₃), sodium arsinite (Na₃AsO₃).

A 14.16

Green chemistry is a way of thinking and is about utilising the existing knowledge and principles of chemistry and other sciences to reduce the adverse effect of pollution. It is a production process that would bring about minimum pollution or deterioration to the environment. In a nutshell, it is a cost-effective approach which involves reduction in material, energy consumption and waste generation.
It will help in decreasing environmental pollution by adopting the following examples:

1. In a chemical reaction, if reactants are fully converted into useful environmental friendly products by using an environment friendly medium then there would be no chemical pollutants introduced in the environment.
2. During a synthesis, care must be taken to choose starting materials that can be converted into end products with yield approximately up to 100 per cent.
3. It may be worthwhile to carry out synthetic reactions in aqueous medium since water has high specific heat and low volatility. Water is cost effective, non inflammable and devoid of any carcinogenic effects.

A 14.17 The solar energy radiated back from the earth surface is absorbed by the green house gases (CO₂, CH₄, O₃, CFCs) present near the earth’s surface.
They heat up the atmosphere near the earth’s surface and keep it warm. As a result of these, there is growth of vegetation which supports the life. In the absence of this effect, there would be no life of both plant and animal on the surface of the earth.

A 14.18

Excessive phytoplankton (organic pollutants such as leaves, grass trash etc.) present in water are biodegradable. Bacteria decompose these organic matters in water. During this process when large number of bacteria decomposes these organic matters, they consume the dissolved oxygen in water. When the level of dissolved oxygen falls below 6 ppm the fish cannot survive.

A 14.19 Domestic waste can be separated into biodegradable and non-biodegradable materials. Non-biodegradable materials such as plastic, glass, metal scraps etc. are sent for recycling.  Biodegradable wastes can be deposited in landfills and are converted into compost to be used as manure.

A 14.20 The compost producing pit should be kept covered so that flies cannot make entry into it and bad odour is minimized.
The waste materials which are non-biodegradable like glasses, plastic bags, plastic bottles, polybags, must be handed over to the vendors who can send them to the recycling plants.