CBSE Class 11 Chemistry Environmental Chemistry Notes Set B

Class XI

Chapter-14

Environmental Chemistry

TOP Concepts:

1. Environmental pollution: It is the effect of undesirable changes in our surroundings th  have harmful effects on plants, animals and human beings.

2. Pollutant: A substance, which causes pollution, is known as pollutant.

3. Pollutants can be solid, liquid or gaseous substances present in greater concentration than in natural abundance.

4. Pollutants can be natural or anthropogenic:

a. Natural pollutants: These are produced due to natural happenings like volcano eruptions etc.

b. Anthropogenic pollutants: These are produced due to human activities.

5. Pollutants can be biodegradable or non – biodegradable:

a. Biodegradable pollutants: These are the pollutants which rapidly break down by natural processes. Example: discarded vegetables

b. Non – biodegradable pollutants: These are the pollutants which are slowly degradable, and remain in the environment in an unchanged form for many decades. For example: DDT, plastic materials, heavy metals, many chemicals, nuclear wastes etc

6. Environmental pollution is of three types:

a. Atmospheric pollution

i. Tropospheric pollution

ii. Stratospheric pollution

b. Water pollution

c. Soil and land pollution

7. Atmospheric pollution occurs when the concentration of a normal component of the air or a new chemical substance added or formed in air builds up to undesirable proportions causing harm to humans, other animals, vegetation and materials.

8. Troposphere: The lowest region of atmosphere in which the human beings along with other organisms live is called troposphere. It extends up to the height of ~ 10 km from sea level.

9. Stratosphere: Above the troposphere, between 10 and 50 km above sea level lies stratosphere.

10.Tropospheric pollution: Is because of two types of pollutants:

a. Gaseous air pollutants: These are oxides of sulphur, nitrogen and carbon, hydrogen sulphide, hydrocarbons, ozone and other oxidants.

b. Particulate pollutants: Particulate pollutants are the minute solid particles or liquid droplets in air. These are present in vehicle emissions, smoke particles from fires, dust particles and ash from industries. Examples of particulate pollutants are dust, mist, fumes, smoke, smog etc.

11. Oxides of Sulphur as pollutant:

Sources: Burning of fossil fuels containing Sulphur

Harmful effects:

· Causes respiratory diseases e.g., asthma, bronchitis, emphysema in human beings.

· Sulphur dioxide causes irritation to the eyes, resulting in tears and redness.

· High concentration of Sulphur dioxide leads to stiffness of flower buds which eventually fall off from plants.

12. Oxides of nitrogen as pollutant:

Sources:

· At high altitudes when lightning strikes, dinitrogen and dioxygen combine to form oxides of nitrogen.

· Burning of fossil fuel in an automobile engine, at high temperature, dinitrogen and dioxygen combine to yield significant quantities of nitric oxide (NO) and nitrogen dioxide (NO₂).

N₂ (g) + O2 (g) 1483K ¾¾¾¾¾® 2 NO (g)
2 NO (g) + O₂ (g) → 2 NO₂ (g)

Harmful effects:

· Damage the leaves of plants and retard the rate of photosynthesis

· Nitrogen dioxide is a lung irritant that can lead to an acute respiratory disease in children

· It is toxic to living tissues also

· Nitrogen dioxide is also harmful to various textile fibres and metals

13. Hydrocarbons as pollutant:

Source: Incomplete combustion of fuel used in automobiles

Harmful effects:

· Hydrocarbons are carcinogenic, i.e., they cause cancer

· They harm plants by causing ageing, breakdown of tissues and shedding of leaves, flowers and twigs

14. Oxides of carbon as pollutant:

a. Carbon monoxide:

Source:

· Incomplete combustion of carbon of coal, firewood, petrol, etc
· By automobile exhaust

Harmful effects:

It is highly poisonous to living beings because of its ability to block the delivery of oxygen to the organs and tissues. It binds to hemoglobin to form carboxyhemoglobin, which is about 300 times more stable than the oxygen-hemoglobin complex. In blood, when the concentration of carboxyhemoglobin 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.

b. Carbon dioxide:

Source:

· Respiration
· Burning of fossil fuels for energy
· By decomposition of limestone during the manufacture of cement
· By volcanic eruptions
· Deforestation

Harmful effects:

· Causes global warming

15. Green house effect: About 75 % of the solar energy reaching the earth is absorbed by the earth’s surface, which increases its temperature. The rest of the heat radiates back to the atmosphere. Some of the heat is trapped by gases such as carbon dioxide, methane, ozone, chlorofluorocarbon compounds (CFCs) and water vapour in the atmosphere. Thus, they add to the heating of the atmosphere. This causes global warming. This trapping of the sun’s heat near the earth’s surface and keeping it warm is called natural greenhouse effect. It maintains the temperature and makes the earth perfect for life.

If the amount of carbon dioxide crosses the delicate proportion of 0.03 per cent, the natural greenhouse balance may get disturbed. This may lead to global warming.

16. Green house: In a greenhouse, visible light passes through the transparent glass and heats up the soil and the plants. The warm soil and plants emit infrared radiations. Since glass is opaque to infrared (heat) radiations, it partly reflects and partly absorbs these radiations. This mechanism keeps the energy of the sun trapped in the greenhouse.

17. Global warming: An increase in the average temperature of the earth's atmosphere (especially a sustained increase that causes climatic changes) which may be caused by additional heat being trapped by greenhouse gases.

18. Acid rain: Normally rain water has a pH of 5.6 due to the presence of H+ ions formed by the reaction of rain water with carbon dioxide present in the atmosphere.

Source: Burning of fossil fuels (which contain sulphur and nitrogenous matter) such as coal and oil in power stations and furnaces or petrol and diesel in motor engines produce sulphur dioxide and nitrogen oxides. SO2 and NO2 after oxidation and reaction with water are major contributors to acid rain, because polluted air usually contains particulate matter that
catalyses the oxidation.

Harmful effects:
• Harmful for agriculture, trees and plants as it dissolves and washes away nutrients needed for their growth.
• Causes respiratory ailments in human beings and animals.
• Affects plant and animal life in aquatic ecosystem when acid rain falls and flows as ground water to reach rivers, lakes etc.
• Corrodes water pipes resulting in the leaching of heavy metals such as iron, lead and copper into the drinking water.
• Damages buildings and other structures made of stone or metal. The Taj Mahal in India has been affected by acid rain.

19. Particulates in the atmosphere may be viable or non-viable:
a. Viable are minute living organisms that are dispersed in the atmosphere. Example: bacteria, fungi, moulds, algae etc.
b. Non-viable particulates may be classified as:
i. Smoke particulates: consist of solid or mixture of solid and liquid particles formed during combustion of organic matter.
Example: cigarette smoke, smoke from burning of fossil fuel,
garbage and dry leaves, oil smoke etc.
ii. Dust: composed of fine solid particles (over 1m in diameter),
produced during crushing, grinding and attribution of solid
materials. Sand from sand blasting, saw dust from wood works,
pulverized coal, cement and fly ash from factories, dust storms etc., are some typical examples of this type of particulate emission.
iii. Mists: Are produced by particles of spray liquids and by condensation of vapours in air. Example: sulphuric acid mist and erbicides and insecticides that miss their targets and travel
through air and form mists.
iv. Fumes: Are generally obtained by the condensation of vapours during sublimation, distillation, boiling and several other chemical reactions. Generally, organic solvents, metals
and metallic oxides form fume particles.

20. Smog: Smoke is a mixture of smoke, dust particles and small drops of fog.

21. Smog is of two types:

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