These notes for CBSE Class 11 Chemistry, Chapter 14, explore Environmental Chemistry, defining it as the study of chemical species in the environment – their origins, movement, reactions, impacts, and eventual fate. The chapter details various forms of pollution, starting with atmospheric pollution, distinguishing between tropospheric and stratospheric issues. It explains global warming and the greenhouse effect, highlighting the roles of gases like CO2 and methane. Acid rain, characterized by a pH below 5.6, and its detrimental effects are examined. The notes differentiate between classical and photochemical smog and discuss the critical issue of ozone layer depletion and its resulting increase in UV radiation. Water pollution is covered extensively, including sources like sewage, industrial waste, and thermal pollution, alongside concepts like eutrophication and Biochemical Oxygen Demand (BOD). Soil pollution from pesticides and herbicides is also addressed. The chapter concludes by introducing Green Chemistry, emphasizing the use of existing knowledge to reduce environmental harm.
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• Environmental chemistry deals with the study of the origin,transport,reactions,effects,fates of chemical species in the environment.
Environmental pollution is the effect of undesirable changes in our surroundings that have harmful effects on plants, animals and human beings.A substance which causes pollution is called a pollutant.they can be solid,liquid or in the gaseous state.
The atmosphere that surrounds the earth is not of the same thickness at different heights.Atmospheric pollution is generally studied as tropospheric and stratospheric pollution.The ozone layer prevents about 99.5%of the sun’s UV rays.
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;
• Gaseous air pollutants:These are oxides of sulphur, nitrogen and carbon, hydrogen sulphide, hydrocarbons, ozone and other oxidants.
• Particulate pollutants; these are dust, mist, fumes, smoke, smog etc
About 75% of the solar energy reaching the earth is absorbed by the earth’s surface,which increases it’s temperature.The rest of the heat radiates back to the atmosphere.Some of the heat is trapped by the gases such as carbon dioxide,methane,ozone,CFCS and Water vapour.they add to the heating of the atmosphere causing Global warming 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 rays,it partly reflects and partly absorbs these radiations,this mechanism keeps the energy of the sun trapped in the greenhouse.
When the pH of the rain water drops below5.6, it is called acid rain.Acid rain is harmful for agriculture, trees and plants as it dissolves and washes away nutrients needed for their growth. It causes respiratory ailments in human beings and animals. When acid rain falls and flows as ground water to reach rivers, lakes etc. it affects plants and animal life in aquatic ecosystem
The word smog is derived from smoke and fog.There are two types of smog:classical and photochemical smog. Classical smog occurs in cool humid climate. It is a mixture of smoke, fog and sulphur dioxide. It is also called reducing smog. Whereas photochemical smog occurs in warm and dry sunny climate. It has high concentration of oxidizing agents and therefore ,it is also called as oxidizing smog.
Depletion of ozone layer is known as ozone hole.
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
contamination of water by foreign substances which make it harmful for health of animals or plants or aquatic life and make it unfit for domestic, industrial and agriculture use.
Sewage and domestic wastes Industrial effluents Agriculture effluents Siltation-mixing of soil or rock into water Thermal pollutants Radioactive discharge
The process in which nutrientenriched water bodies support a dense plantpopulation, which kills animal life by deprivingit of oxygen and results in subsequent loss ofbiodiversity is known as Eutrophication.
The amount of oxygen required by bacteria to break down the organic matter present in a certain volume of a sample of water, is called Biochemical Oxygen Demand (BOD)
Insecticides, pesticides and herbicides cause soil pollution.
Green chemistry us a way of thinking and is about utilizing the existing knowledge and principles of chemistry and other sciences to reduce the adverse impact on environment.Green chemistry is a production process that would bring out minimum pollution or deterioration to he environment..Utilization of existing knowledge base for reducing the chemical hazards along with the development of activities is the foundation of
green chemistry.
Environmental Chemistry is the study of the origin, transport, reactions, effects, and fates of chemical species in the environment.
Global warming is caused by heat being trapped in the atmosphere by gases like carbon dioxide, methane, ozone, CFCS, and water vapour, which absorb and re-emit heat radiated from the Earth's surface.
Acid rain is defined as rain with a pH below 5.6, which is harmful to agriculture, plants, and aquatic life.
The two types of smog are classical smog (reducing smog, found in cool, humid climates) and photochemical smog (oxidizing smog, found in warm, dry, sunny climates).
Ozone layer depletion allows more UV radiation to reach the troposphere, leading to skin ageing, sunburn, skin cancer, and damage to aquatic life and fish productivity.
BOD (Biochemical Oxygen Demand) is the amount of oxygen required by bacteria to break down organic matter in a water sample.
Green Chemistry is a way of thinking and applying existing knowledge and principles of chemistry and other sciences to reduce the adverse impact of production processes on the environment.
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