NEET Study Notes on Environmental Chemistry: The scientific study of biological, physical, chemical components of the environment is known as environmental chemistry. With the study of environmental chemistry, we are able to find out the causes of degradation in the environment and ways to minimize it.

• The environment can be further classified into- Atmosphere, Hydrosphere, Lithosphere and Biosphere. Pollution in Environment is caused by Pollutants.
• These Pollutants Primary or Secondary Pollutants. In this article, we will also discuss Green chemistry that can be utilized as an alternative tool to keep a check on pollution.
• On average, the number of questions from environmental chemistry varies from 2to 3. A thorough revision from these notes will help you in revision for NEET 2022.
• The overall weightage from Organic Chemistry is around 34% which makes it an important section in NEET Chemistry Syllabus.

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NEET Study Notes for Environmental Chemistry: Important Topics

Pollution and Pollutants

Pollution is defined as the degradation of the environment due to the action of certain substances. These substances are known as Pollutants, Pollutants may be released in solid, semi-solid, liquid, gas, or molecular form.

Pollutants may be classified into Natural and Anthropogenic Pollutants.

Natural Pollutants include forest fires, mine fires, floods, volcanic eruptions, radioactive substances, etc

Anthropogenic Pollutants include those pollutants that come into play as a result of human activities. These can be further classified into Primary and Secondary Pollutants.

• Primary Pollutants- These are those pollutants that are emitted from the source directly into the atmosphere. Examples of Primary Pollutants include inorganic gases such as SO₂, CO, NO, radioactive substances, particulate matter like smoke ash dust and fume.

• Secondary Pollutant- Primary Pollutants reacting with other constituents in the atmosphere give rise to secondary pollutants. Examples of some of the secondary pollutants include NO₂, CH₄, aldehydes, ketones, nitrates.

Also Read:

• NEET Study Notes for Chemical Equilibrium

• NEET Study Notes for Dual Nature of Matter and Radiation

Air Pollution

The existence of or the emission of foreign particles, gases and pollutants that affect the quality of air adversely is known as air pollution. Air pollutants can be classified into gases and particulates.

• Gaseous materials include gas and vapor of compounds or substances. The boiling point of such substances is below 200° Celsius.
• Particulate matter is those solid particles or droplets of liquids that are so small that they tend to remain in the air suspended. Examples- are soot, dust, smoke, dust mites.
• These suspended particles in the troposphere pose harm to humans in the form of respiratory illnesses like bronchitis, asthma, etc.

Major Air Pollutants

• Carbon Monoxide- Incomplete combustion of gasoline in motor vehicles, coal, wood, forest fires. Carbon monoxide is an extremely toxic gas as the transport of oxygen is blocked from lungs to other parts of the body. Thus it causes respiratory illness.
• Sulphur Oxide- Sulphur oxide is emitted due to the action of petrol combustion, petrol refining, coal combustion, smelting operations, oil refineries.
• Nitrogen Oxide- Fossil fuel burning releases large amounts of nitrogen oxide. Nitrogen Oxide is responsible for Acid Rain.

Soil Pollution

The addition or removal of substances that cause soil productivity decreases, plants quality, groundwater is called soil pollution.

Pollutants of soil are- industrial wastes, pesticides, fertilizers, food, paper, glass, plastics.

• Pesticides- Pesticides are also known as biocides. These are chemical substances to control the growth of unwanted organisms are called pesticides. These can be further classified as insecticides, fungicides, herbicides, rodenticides etc.
• Fertilizers- Fertilizers are composed of mainly plant nutrients like K, N and P. However excess use of fertilizers depletes the nitrogen-fixing bacteria.
• Radioactive waste- Radioactive waste that is emitted due to research activities. Plants, animals and other organisms are affected adversely by radioactive waste.
• Industrial Wastes- Industries dump a lot of their waste in over the soil which increases the toxic levels of the soil. Industrial waste contains substances like alkalies, chromates, metals (copper, mercury, zinc, lead) etc.

Soil Pollution can be controlled by controlling the disposal of such wastes, effective use of chemical fertilizers, and biological pest control. Soil Pollution can also be controlled by other measures like restoration of food, improving draining and crop rotation.

Read NEET Study Notes for Reaction Mechanism

Smog

When a composition of tiny particulate matter like carbon, ash, oil from the combustion of coal, called smoke and food in the form of suspended droplets is combined, it results in fog.

• Silvering, glazing in plants and bronchitis. asthma is caused in humans due to smog.
• Smoke can be classified into two types- Classical Smog or Sulphurous Smog and Photochemical Smog.
• Classical Smog occurs at temperatures that are low. It is identified by the absence of secondary pollutants and composes of H₂S, smoke and dust particles.
• Photochemical smog- occurs at high temperatures when two air pollutants nitrogen oxides and hydrocarbons react in the existence of sunlight UV radiations. This produces ozone and peroxyacetyl which are components of photochemical smog.

Acid Rain

The precipitation of nitric and sulphur acids in harmful amounts, that are mainly formed from nitrogen oxides and sulphur oxides and released in the atmosphere is called Acid Rain.

• These oxides get converted into acids on coming in contact with the water vapour in the presence of oxygen in the atmosphere.
• The ph of acid rain is reduced to 5.5.

• Acid rains damage buildings and are harmful to vegetation.

Read:

• NEET Study Notes on Organic Chemistry

• NEET Study Notes on Chemical Bonding

Greenhouse Effect

The retention of heat from the sun by earth and prevention of such heat escape is termed as the greenhouse effect.

• Certain greenhouse gases like ozone, methane, chlorofluorocarbons and water vapour form a cover around the earth to prevent the escape of IR Rays from the earth.
• The main greenhouse gases are CO₂, CH₄, N₂O and SO₂, NO₂, O₃, water vapour released from industries and agriculture activities also lead to an increase in the greenhouse effect.
• Effects of Global warming include- harmful effects on weather and climate, Sea Level change, effect on species distribution range, food production.
• Global warming results in a change in precipitation patterns, This rapid change in climate adversely affects the health of humans.
• The sea-level changes and glaciers melt due to global warming.
• An increase in temperature also causes weed growth which leads to a decrease in the production of growth.
• In order to deal with global warming, an increase in vegetation cover will lead to utilization of CO₂.
• Fossil fuels usage should be minimised as this will reduce the emissions of greenhouse gases.
• The use of nitrogen fertilizers should be reduced to reduce the emission of nitrous oxide.
• To minimise and reduce the effect of global warming, chlorofluorocarbons should be replaced.

Green Chemistry as an Alternative Tool for Reducing POllution

Utilization and Analysis of advanced skills, knowledge to curb the harmful effects of pollution on the environment is a process known as Green Chemistry. Green Chemistry, also known as Sustainable chemistry reduces the effects of operations that lead to development.

The main difference between environmental chemistry and green chemistry is that while environmental chemistry informs us about the chemistry impact and formation of long-term solutions for the environment, green chemistry helps us to see the consequences of the development actions clearly. The development processes are required for our survival, however, the need to take these development processes ahead without much damage to the environment gives rise to the term Green Chemistry.

Twelve Principles of Green Chemistry

American chemists, Paul Anastas and John Warner in 1998 provided the basis of green chemistry. The twelve principles of green chemistry as an alternative tool for reducing pollution are

• Waste Prevention- With the technological advancements in treating waste, it is essential to realize that the first step is to minimize the waste that is produced as a byproduct of human activities.
• Atom Economy- The number of atoms that are combined in the final product should be minimised, Reaction efficiency can be achieved by adopting the concept of atom economy.
• Production of less hazardous chemicals- Chemical reactions and their synthesis process should be designed in a way so that is safe.
• Design chemicals that are safe- Synthesis of chemicals in a safe manner is a process of later stage, however, production of safe chemicals should also be focused upon.
• Design safe solvents and auxiliaries- Steps should be taken to use safe solvents. Solvents and auxiliaries contribute in a large extent to waste so they should be utilized effectively.
• Energy Efficiency- The energy that is utilized in any process should be minimized. Heating and cooling should be avoided or minimized in any process.
• Usage of Renewable Raw Material- Chemicals that are renewable and originate from plant-based sources should be used rather than direct usage of chemicals whose origination is from petrochemical sources.
• Reduction in Derivatives- Derivatives should be minimized as they lead to the addition of waste created.
• Usage of Catalytic Raegants- Catalytic Raegants should be used in reactions. As this will help in minimizing waste, reducing energy and reaction time.
• Degradation Design- Chemicals should be designed in a way that they can be disposed of easily without harming the environment.
• Preventing Pollution in Real-Time- Chemical reactions should be analyzed in real-time so that release of any polluting substances can be prevented in real-time.
• Incorporating safe chemistry for accident prevention- Chemical procedures that are safe and do not bear the risk of accidents should be adopted. Any risk should be assessed prior to the occurrence of the reaction.

Must Read:

• NEET Study Notes for Redox Reactions

• NEET Study Notes for Hydrogen

Some Applications of Green Chemistry

• Bleaching Paper- Usage of Hydrogen Peroxide in the place of chlorine gas is being used for bleaching action these days.
• Dry cleaning clothes- Usage of liquified carbon dioxide has replaced tetrachloroethylene which is carcinogenic in nature and pollutes the environment.
• Specialized Synthetic Technique Development- Asymmetric synthesis, or enantioselective synthesis with the incorporation of Hydrogen.
• Production of Hydrazine by peroxide process wherein ammonia reacts with hydrogen peroxide, producing water as a side product, This process does not require any auxiliary solvents.

NEET Sample Questions on Environmental Chemistry

Question: What is Smog?

1. Fog and Ozone
2. Ozone and smoke
3. Fog and Smoke
4. Vehicular Pollutants

Answer: Fog and Smoke

Question: Where are ozone holes more prominent?

1. Tropic of Cancer
2. Tropic of Capricorn
3. Equator
4. Poles

Answer: Poles

Question: Which is not a greenhouse gas?

1. Carbon Dioxide
2. Oxygen
3. Water vapor
4. Methane

Answer: Oxygen

Question: Which synthetic chemical depletes the ozone layer?

1. Methanol
2. Biopolymer
3. Chlorofluorocarbons
4. Polyvinylchloride

Answer: Chlorofluorocarbons

Question: What does Photochemical smog not contain?

1. Acrolein
2. Peroxyacetyl Nitrate
3. Chlorofluorocarbons
4. Ozone

Answer: Chlorofluorocarbons

Question: What is DDT?

1. Antibiotic
2. Biodegradable Pollutant
3. Non-Biodegradable Pollutant
4. Nitrogen-containing Insecticide

Answer: Non- Biodegradable Pollutant

Question: Which is not a greenhouse gas?

1. Nitrogen
2. Methane
3. Carbon dioxide
4. Ozone

Answer: Nitrogen

Question: Which among the following is a secondary pollutant?

1. PAN
2. N₂O
3. CO₂
4. SO₂

Answer: PAN

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