CBSE Class 11 Chemistry Revision Notes Chapter 14

Class 11 Chemistry Revision Notes for Chapter 14 – Environmental Chemistry

For Class 11 students, Environmental Chemistry or Environmental Science is a crucial chapter because it approaches environmental issues from a chemical perspective. The study of reactions, origins, effects, and generally the fate of species in the environment are also discussed in this chapter. Since the subchapters are vast, students must understand and note important points for quick revisions. Taking this into consideration, Extramarks provides concise and reliable Class 11 Chemistry Chapter 14 Notes. The notes are written by subject matter experts, which makes them a valuable resource for students to understand complex concepts.

Revision Notes for Class 11 Chemistry Chapter 14 – Environmental Chemistry – Free Download

Access Class 11 Chemistry Chapter 14 – Environmental Chemistry

The surroundings that we live in include the air, water, soil, vegetation, and atmosphere. The branch of chemistry known as environmental chemistry studies how living things interact with their environment.

1. Introduction

This chapter will enable students to :

• learn what environmental chemistry means, what atmospheric pollution is, and what causes global warming; 
• understand environmental pollution and acid rain;
• identify the causes and effects of ozone layer thinning;
• explain the causes of water pollution and be knowledgeable about global standards for drinking water;
• enumerate the root causes of soil pollution;
• propose and implement environmental pollution control measures;
• acknowledge the significance of green chemistry in daily life.

2. Defining Environmental Chemistry 

The study of the origin, movement, reactions, outcomes, and fates of chemical species in the environment is known as environmental chemistry.

3. Pollution Effects:

1. Approximately 3000–4000 people died as a result of the London smog.
2. The illness “Minamata,” was brought on by mercury contamination in the waters surrounding Minamata Island which spread after people consumed fish caught there. This has affected a large number of people in Japan.
3. Methyl isocyanate (MIC), a gas that caused thousands of deaths in 1984, leaked from a union carbide factory in Bhopal.
4. Numerous buildings in Italy, especially in Rome, are being destroyed by acid rain.
5. The Mediterranean Sea has degenerated into a “dead sea” and can no longer sustain aquatic life.
6. A special board has purified the holy River Ganges in India.
7. Air pollution is brought on by hazardous radiations released by nuclear weapons testing and radioactive fallout from reactors.
8. The Taj Mahal’s beauty is declining due to air pollution.
9. During World War II, the atomic bomb in Japan caused thousands of deaths in the cities of Hiroshima and Nagasaki.
10. Nuclear pollution had a greater impact on Chornobyl’s population.
11. The mishap at the Visakhapatnam oil refinery of HPCL.
12. The unintentional forest fire in Indonesia severely harmed the environment.

4. Definition of Terms:

• Pollutant:

A natural substance that has increased in quantity due to human activity and has a detrimental effect on the environment is referred to as a pollutant. For instance, lead, mercury, sulphur dioxide, carbon dioxide, and so forth.

• Contaminant:

Chemicals that are not present in nature but are released into the environment as a result of human activity are referred to as contaminants. For instance, the union carbide factory in Bhopal was the source of the deadly gas methyl isocyanate (MIC).

• Receptor:

A medium that is impacted by pollutants is called a receptor.

• Sink:

A sink is a substance that interacts with the pollutant and lessens the impact of pollution.

• Organisms that eat dead animals or convert trash and dry leaves into fertiliser.
• A significant carbon dioxide sink is seawater. Furthermore, plants are excellent CO2 sinks.
  • The classification of various contaminants according to their level of toxicity is known as speciation.
  • Alkylated mercury is less dangerous than pure mercury. Comparatively speaking to lead, mercury compounds are toxic.

• Oxygen Dissolved (D.O.)

1. The quantity of oxygen present in water that is dissolved is known as dissolved oxygen (D.O.).
2. 46mgL1 of oxygen must be present in water for healthy plant and animal growth.
3. The water is regarded as contaminated when the D.O. value in waterfalls is less than 5 ppm.
4. Water pollution decreases with increasing DO values and vice versa.
5. The D.O. value decreases as the temperature rises.

• B.O.D. (Biochemical Oxygen Demand)

1. Biochemical oxygen demand is the amount of oxygen needed by bacteria and other microorganisms to break down organic matter in aerobic (oxygen present) conditions at a particular temperature (BOD).
2. Clean water has a B.O.D. value of 3 ppm.
3. Compared to pure water, impure water has a higher B.O.D. value (>3 ppm).
4. Municipal sewage has a BOD value that ranges from 100 to 4000 ppm.
5. Aquatic species such as fish and plants perish when BOD levels are high in the water.

• COD (Chemical Oxygen Demand):

1. The amount of oxygen that reactions in a given solution can potentially consume is roughly estimated by the chemical oxygen demand (COD). It is frequently expressed as the volume of the solution divided by the mass of oxygen used.
2. The COD value is a significant factor in determining the quality of the water.
3. Potassium dichromate can be 50% acidified to produce the above O2.
4. The more the environment is contaminated, the higher the COD value.

• TLV (Threshold Limit Value):

1. The threshold limit value is the lowest concentration of dangerous substances or pollutants in the air that can be harmful to a person when they are inhaled for eight hours each day at work (TLV).
2. TLV is the maximum allowable level of pollutants in mining and industrial areas.

5. Environment Segments:

The environment has four segments:

• a) Atmosphere b) Hydrosphere c) Lithosphere d) Biosphere

• A) Atmosphere:

1. The air layer that covers the entire planet is known as the atmosphere.
2. The earth is protected by the atmosphere. It transmits near-ultraviolet, visible, and near-infrared radiation while absorbing a portion of the electromagnetic radiation from the sun.

• B) Hydrosphere:

1. The portion of the earth’s water that is present is known as the hydrosphere. 
2. Four-fifths of the earth’s surface is covered in water.
3. The hydrosphere is composed of 97 per cent seawater, and 3 per cent ice from the polar ice caps, and the remaining water is used for drinking and agriculture. 
4. Seawater can support a variety of marine life, despite not being drinkable.

• C) Lithosphere:

1. Except for the hydrosphere, land makes up the majority of the rest of the earth’s space known as the lithosphere. 
2. The lithosphere is home to plants, animals, and people, and the innermost layers of the earth’s surface contain minerals.

• D) Biosphere:

1. All living things, including plants, animals, and people, make up the biosphere. 
2. There are connections between the biosphere and other environmental factors. 
3. All interactions between biological systems and their surroundings are referred to as ecosystems. 
4. The biosphere is interconnected with other elements of the ecosystem.

• I) Troposphere (0-11km):

1. The troposphere is found up to 11 kilometres above the surface of the earth.
2. Given that it contains air, it is the most significant component of the atmosphere.
3. The temperature and air density decrease as altitude increases.

• II) Stratosphere:

1. The stratosphere is the atmosphere’s topmost layer (11-50 km)
2. This zone is located between 11 and 50 kilometres above the surface of the earth. It contains an ozone layer.
3. Sunlight’s ultraviolet (UV) energy is absorbed by the ozone layer, keeping it from reaching the earth. As a result, it acts as a layer of protection.

III) Mesosphere:

1. It is located 50 to 85 kilometres above the surface of the earth.
2. In this region, sound waves cannot travel.

1. IV) Thermosphere (Ionosphere):

1. It can be found between 85 and 500 kilometres above the surface of the planet.
2. The temperature in this area rises to a maximum of 1473 K as we ascend higher.
3. The ionisation of atmospheric oxygen occurs after solar energy absorption.

6) Air Pollution:

1. The three main elements that makeup air are nitrogen, oxygen, and water vapour.
2. Carbon dioxide and argon are minute airborne particles.
3. Neon, helium, methane, krypton, nitrous oxide, hydrogen, xenon, sulphur dioxide, ozone, and ammonia are a few of the trace gases found in the atmosphere.
4. The air’s pressure and density decrease as we ascend above the surface of the planet.
5. Significant air pollutants include carbon oxides like carbon dioxide and monoxide. Nitrogen oxides, sulphur oxides, ozone, chlorofluorocarbons (CFCs), and hydrocarbons (methane, butane, etc.) are additional pollutants. 
6. Metals such as lead and heavy metals are organic pollutants.

• Carbon Monoxide (Co) :

1. Incomplete combustion of gasoline and diesel at high pressures and temperatures in motor vehicles results in the production of smoke. Most of this smoke is made up of carbon monoxide.
2. When the organic material in fuel dissociates, methane is created. By oxidation, this methane also becomes carbon monoxide.
3. Although the safe level of carbon monoxide in the air is 9 ppm, peak hours in urban areas can see levels as high as 50–100 ppm. When CO and blood haemoglobin interact, carbonyl wash arms haemoglobin is created, which is incapable of carrying oxygen.

• Nitrogen Oxides:

1. Oxides of nitrogen – The most prevalent nitrogen oxides that pollute the air are NO2 and N2O.
2. When fossil fuels and auto fuels are burned, nitrogen oxides are released.
3. The legal limit for nitrogen oxides is 10 ppm. At concentrations greater than 10 ppm, photosynthesis cannot be carried out by plants.
4. When ozone and nitric oxide interact, the ozone (O3) breaks down into oxygen (O2).

• Sulphur Oxides:

1. When burned, sulphur, sulphide ores, ores, and fuels containing sulphur release SO2 into the atmosphere.
2. Humans who are exposed to SO2 develop respiratory illnesses, because SO2 harms the mucous membranes in the nose and respiratory tract.
3. The leaves of plants turn from green to yellow when exposed to SO2. As a result, plants are unable to photosynthesize.

• Freons Of Chlorofluorocarbons (Cfcs):

1. Chlorofluorocarbons (CFCs), also known as “freon,” are synthetic chemicals made of carbon, fluorine, and chlorine.
2. The most significant chlorofluorocarbon CFCl3 is trichlorofluoromethane.
3. Chlorofluorocarbons (CFCs) are frequently used as solvents, foaming agents, and propellants for refrigerants.
4. In the stratosphere, CFCs absorb UV radiation and decompose into radicals.

• Hydrocarbons:

1. Hydrocarbon methane is widely distributed throughout the world.
2. Various hydrocarbons, including methane, ethane, acetylene, propane, butane, and others, are found in car exhaust.
3. The carcinogenic substance benzopyrene is produced by diesel engines.
4. Peroxyacetyl nitrate is a dangerous chemical that harms plants (PAN).

• Metals:

1. Auto exhaust gases can contain lead particles.
2. In industrial gases, carbon is found as “aerosol” particles.
3. Metal manufacturing plants release metal ions into the atmosphere.
4. When gasoline is burned, lead particles are released into the air if the fuel contains tetraethyl lead, methylene chloride, or ethylene bromide.

• Photochemical Smog:

1. Smoke and fog are referred to as smog.
2. The first location where photochemical smog was identified was Los Angeles.
3. Summer smog is oxidising smog because it contains oxidising chemicals.

• Carbon Pollutants:

1. Pesticides, biocides, and benzo a pyrene are examples of organic air pollutants.
2. During the manufacturing process, businesses release hazardous pesticides and biocides into the air, polluting the environment and posing minor to serious health risks.

• Dust:

1. There are 22 metals in the air, mostly in the form of dust.
2. While calcium, silicon, aluminium, and iron are prevalent in the atmosphere, metals like zinc, copper, magnesium, and manganese are less prevalent.
3. Numerous industries and heavy traffic both contribute to dust pollution.

7) Effects of Air Pollution:

The risks listed below may arise as a result of air pollution: a) acid rain; b) ozone layer depletion; c) greenhouse effect or global warming.

• A) Acid Rain:

1. Acid rain is a result of the reaction between nitrogen and sulphur oxides, which produce nitric and sulfuric acid.
2. Nitric and sulfuric acid-containing rain are known as “acid rain.”
3. Urban areas are more likely to experience acid rain.
4. In 1918, acid rain had a pH of about 5, but by 1962, it had dropped to 4.2.
5. Because of acid rain, building lifespans will be significantly shortened.
6. Acid rain’s impact on marble stones damages the Taj Mahal’s splendour.

• B) Depletion in the Ozone Layer:

1. Near the earth’s north and south poles, the O3 layer has holes due to CFCs.
2. A 3 per cent increase in ultraviolet light falling on the earth results from ozone layer loss.
3. Plant photosynthetic processes are impacted by UV rays.

• C) Global Warming or The Greenhouse Effect:

1. Carbon dioxide and water vapour absorb infrared radiation that is emitted by the sun and is partially reflected by the earth’s surface. As a result, the surface of the earth becomes warmer. The phenomenon of the earth’s surface heating up is known as the greenhouse effect.
2. There is an increasing level of CO2 in the atmosphere.
3. Deforestation is leading to an expansion of the atmosphere.
4. In the stratosphere, ozone acts as a protective layer; however, in the troposphere, it is harmful.
5. More sinks must be produced by establishing forests and planting trees to stop global warming.
6. There is 0.03 percent of carbon dioxide in the atmosphere.
7. Organic pollutants include waste from industry and agriculture.
8. Examples of organic contaminants include plastics, fibres, detergents, paints, peroxides, pesticides, weedkillers, dyes, plasma chemicals, and others. Pulp, sugar, paper, and leather are examples of industrial waste.

• Fluorides:

1. Fluorides are safe in drinking water at levels up to 3 ppm.
2. Fluoride concentration should have lower and upper bounds of 1 ppm and 3 ppm, respectively.
3. Fluorine levels can be determined using the zirconium Alizarin-S dye.
4. The Indian state’s Nalgonda, Prakasam, and Guntur districts’ drinking water contain an excessive amount of fluorine.

1. Drinking Water Defluoridation Techniques:
2. The process of removing fluoride ions from water is referred to as defluoridation.
3. Bleaching powder, lime, and alum are combined with water and kept. The complex calcium aluminium fluoride forms from the fluoride ions in the water. To obtain pure water, this is filtered. This technology was developed by NEERI (National Environmental Engineering Research Institute).

Our Responsibility to the Environment:

1. Utilising microorganisms and enzymes, many waste materials, including plastics, can be broken down.
2. Any reaction produces pollutants as a byproduct. Therefore, processes that have no byproducts and produce an environmentally friendly reaction should be developed.
3. It is necessary to use unconventional fuels and unconventional energy sources instead of conventional fuels and energy sources.
4. Technology that is environmentally friendly and clean should be created and used.
5. Population growth must be controlled.