WBCHSE Class 11 Chemistry Environmental Chemistry Notes

Class 11 Chemistry Environmental Chemistry Introduction

The word ‘environment’ derived from the French word ‘environment can be defined at an assembly of physical, chemical and biological factors, which act upon an organism or an ecological community to determine its form and mode of survival.

Environment mainly consists of three major components:

1. Biotic or living: 
   • For example – All living creatures)
2. Abiotic or non-living:
   • For example –  Lithosphere, hydrosphere and atmosphere) and
3. Energy components: 
   • For example – Solar energy, thermochemical energy, nuclear energy etc.)

Environmental Chemistry

Environmental Chemistry Definition

The branch of science, which deals with the sources of the chemical components of the environment, the chemical reaction occurring among them, the products formed in the reaction and their impact on the living world is called environmental chemistry.

The study of environmental chemistry is important because

• It makes us aware of the adverse effects of various chemical constituents on the environment.
• It gives us an idea about the toxic effects of various chemical substances and their by-products which are extensively used to fulfill our requirements.
• It gives us an idea about the sources of various toxic chemicals, their adverse effects and the antidotes to combat their toxicity.

1. Some terms used in environmental chemistry

1. Pollutant:

A pollutant is a solid, liquid or gaseous substance (produced either by natural sources or by human activity) which is present in the environment to such an extent that it causes harmful or detrimental effects on living organisms (plants, animals and human beings) or nonliving components.

Example:

Air contains trace amounts of CO (0.1 ppm). If, for any reason, the amount of CO increases to 40 ppm or more, then it is regarded as pollutant

Pollutants are of two kinds :

1. Primary pollutant:  The pollutants which are emitted from any source, directly escape into the environment without sustaining any change are called primary pollutants.
2. Example: S, NO, NO₂, CO, CO₂, hydrocarbons etc.
3. Secondary pollutant: There are some pollutants which do not appear in the environment directly from their source. They are produced as harmful substances by Interaction with pollutants), already present in the environment. Tills type of pollutants are called secondary pollutants.
4. Example: Peroxyacyl nitrate (PAN), dimethyl mercury [(CH₃)₂Hg]

2. Biodegradable pollutants

The pollutants which are decomposed by bacteria or germs are known as biodegradable pollutants.

Examples: Household garbage, cow dung and other biomass etc.

3. Non-biodegradable pollutants:

The pollutants which are not decomposed by bacteria or germs or decomposed very slowly are known as non-biode gradable pollutants.

Example:

Mercury, DDT, Gammaxene etc. The presence of these substances even in trace amounts is injurious to human beings and other animals.

4. Contaminant:

A contaminant is a substance which does not occur in nature under normal conditions but is introduced into the environment either accidentally or through indiscriminate human use.It may or may not be harmful to the living organisms or non-living components. The contaminant is considered as a pollutant when it has some harmful effect

Examples:

• In Delhi pyrosulphuric acid (H₂S₂O₇) leakage from a defective tank killed many persons and caused skin and breathing problems to many others. As pyrosulphuric acid does not occur in the atmosphere, therefore it is a contaminant. Again, because of its dangerous effect, it is also regarded as a pollutant.
•  In Kerala, in 1953, 108 people died after consuming wheat flour contaminated with parathion (an agricultural pesticide).

5. Source:

The source ofany contaminantis a chemical substance or the place from whereitis produced.

Example:

A source of the pollutants like CO, NO etc., is the gas 2 emitted from petrol or diesel automobile engines

6. Sink:

If any medium continuously reacts with a pollutant for a long period and causes destruction to it, then it is said to be the sink of that particular pollutant.

Examples:

1.  Sea water acts as a sink of CO₂ present in the atmosphere

⇒ H₂O (sink) +CO₂ (Pollutant ) H₂CO₃

2. An automobile wall or memorial acts as a sink of sulfuric acid, present as an atmospheric pollutant.

⇒ (Sink )CaCO₃+ (polluntant)H₂SO₄→CaSO₂↓ + H₂O + C₂O

7. Receptor or target:

If any plant or animal body or any biotic component is adversely affected by a pollutant, then that particular body or component is called a receptor or the target of that pollutant.

Examples:

•  Smoke or smog causes a burning sensation in our respirator tract and eyes.In this case, man is the receptor or target of smoke or smog.
• The aquatic animals are the receptors of the oil layer, floating on the surface of seawater.

8. Pathways Of pollutants:

The mechanism by which any pollutant is liberated from its source, spreads in the environment and ultimately gets destroyed, is called the pathway of that pollutant.

Example:

Nitric oxide, a pollutant, liberated from petrol or diesel engine reacts with oxygen present in the air to form nitrogen dioxide. Nitrogen dioxide reacts with rainwater and falls on the surface of the earth as nitric acid.

2NO + O₂ → 2NO₂; 2HNO₂+O₂→2HNO₃

2NO₂ + H₂O→HNO₃ + HNO₂

9. Threshold Limit Value (TLV):

Anypollutantin in the environment is considered to be harmful to living organisms if its concentration exceeds a particular limit. This particular limit (of concentration) is called ‘threshold limit value’ (TLV) ofthat particular pollutant.  Atmosphere

Examples: Threshold limit values for CO and CO₂ are. 40 ppm and 5000 ppm respectively. Ho However, the TLV for phosgene (COCl₂) is only 0.1 ppm.

Threshold limit value for factory workers: It is the maximum limit of a pollutant present in the environment maximum limit of a pollutant present in the environment hours per day without suffering from health hazards Examples: Threshold limit values for SO₂ and CO₂ are 5 mg^-3. m^-3 and 5000 mg m^-3 respectively

Air Pollution

When one or more undesirable chemical substances produced by natural phenomena or uncontrolled human activity get mixed with the air to bring about health hazards to human or any other living being and affect their life processes, then air pollution is said to have occurred. The substances which cause air pollution are called air pollutants

Examples:

Sulphur dioxide (SO₂), carbon monoxide (CO), carbon dioxide (CO₂), nitric oxide (NO), nitrogen dioxide (NO₂), hydrogen sulphide (H₂S), hydrocarbons (C_xH_y), ammonia (NH₃), fly ash, dust particles, smoke, fumes etc., are some air pollutants

Causes of air pollution

Natural causes of air pollution:

• Emission of SO₂, CO, H₂S gases etc., due to volcanic eruption.
• Gases liberated due to the decomposition of living bodies.
• Dust storm, forest fires and the fall of a meteorite.
• Spreading of virus, bacteria, fungus, pollen-grain of flowers in air etc

Causes of air pollution due to human activities:

• Sulphur dioxide gas, carbon monoxide gas and fly ash produced from thermal power plant.
• Gases such as sulphur dioxide, sulphur trioxide, oxides of nitrogen, hydrogen chloride, chlorine etc., from acid manufacturing factories.
• Ammonia gas liberated from fertiliser factories and cold storages.
• Sulphur dioxide, carbon monoxide and different metallic oxides obtained during extraction of metals.
• Fine and bulky solid particles produced in cement and asbestos factories.
• Carbon monoxide, nitrogen dioxide, sulphur dioxide and other such gaseous substances evolved from petroleum refineries.
• Dust and sand in the region of coal mines.
• CO, SO₂ and oxides of nitrogen released from motor vehicles.
• Extensive deforestation affects the balance of oxygen and carbon dioxide and increases the quantity of carbon dioxide.
• Highly poisonous gas evolved from destructive weapons used in warfare.0 Emission of radioactive rays due to accidents in nuclear reactors, nuclear power plants etc.
• The extensive use offossil fuel resultsin evolution of gaseous pollutants.

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Major Air Pollutants

Major air pollutants are divided into two classes:

1. Inorganic and organic gaseous substances and
2. Particulates.

Inorganic and organic gaseous substances

1. Carbon monoxide (CO):

Natural sources:

• During volcanic eruptions,
• Due to decomposition of dead plants and animals in marshy land,
• During forest fires,
• During the extraction of petroleum and natural gases,
• During lightning, carbon monoxide is produced.

Man-made sources:

• Incomplete combustion of fuel in automobile engines,
• Incomplete combustion of carbonaceous matter in industrial furnaces,
• Incomplete combustion of agriculture and slash materials,
• Heating of carbon dioxide at a high temperature in the presence of coke in the blast furnace produces carbon monoxide. Sulphur dioxide (SO₂)

Harmful effects:

This colourless, odourless gas is very harmful

Natural sources:

For human beings and animals. It has a greater affinity towards haemoglobin than of oxygen. So, it readily combines with haemoglobin to give a stable compound, carboxyhaemoglobin

(HbO₂ + CO ⇌ HbCO + O₂ ).

• Consequently, oxygen carrying capacity of haemoglobin decreases which ultimately results in death.
• The presence of CO even in small amounts may result in nausea, headache, dizziness etc.
• Cigarette smoke contains a considerable amount of CO which ultimately increases CO content in the smoker’s blood.
• Thus, chain smokers often suffer from mental imbalance, headaches, heart attacks etc. Acute oxygen starvation in the body due to poisoning by CO is called anoxia or asphyxiation.

Sink of carbon monoxide:

• Some bacteria present in the soil absorb CO and convert it to CO₂.
• Inorganic radicals like HO and HOO, atomic oxygen and ozone oxidise CO to CO₂

Control of CO pollution: 

1. One of the main sources of CO pollution is the use of internal combustion engines in automobiles. These engines emit a mixture of CO, NO_x, hydrocarbons and particulates.
   • In order to control the CO emission suitable modifications have to be done in internal combustion engines
   • The carburettor is to be adjusted so as to give a proper air fuel ratio
   • Catalytic converters can be fitted into the exhaust pipe which may bring about oxidation of CO to CO₂ .
   • Internal combustion engines should be modified and improved. Some automobile makers have improved automobile engines by the use of an extra combustion chamber so that fuel undergoes complete combustion and the exhaust gas does not contain CO.
2. CNG, LNG, LPG and LHG (liquefied hydrogen gas) should be used instead of gasoline.
3. Alternative power sources such as fuel cells, solar energy etc., be used.

2. Oxides of sulphur (SO_x):

Two oxides of sulphur, sulphur dioxide (SO₂) and sulphur trioxide (SO₃) are represented by the general formula SO_x. Both of them are colourless gases having suffocating odour.

Sulphur Dioxide (SO₂)

Sulphur Dioxide (SO₂)

Natural sources of  SO₂:

SO₂ gas is liberated in the atmosphere due to volcanic eruptions. 67% of the total SO₂ content of the atmosphere is contributed from this source.

Sources created by human activities:

1. Combustion of coal in thermal plants produces SO₂ gas in abundant quantities.
2. SO₂ gas is evolved during roasting of sulphide ores
3. For example:  FeS, CuFeS₂, Cu₂S, ZnS, PbS etc.) in the extraction of metals.
4. Smoke emitted from oil refineries and automobile engines contains a large quantity of SO₂

Harmful effects of SO₂ :

SO₂ is a gas having extremely pungent and suffocating odour. It adversely affects the respiratory system and causes a burning sensation to eyes.

• If inhaled, it may lead to breathing problems, asthma and bronchitis.
• The presence of excess SO₂ in the atmosphere may result in lung cancer.
• SO₂ also causes allergies.
• In the presence of metallic oxide or other catalysts,  SO₂ reacts with oxygen present in the air and water vapour to form H₂SO₄.
• This sulphuric acid is much more harmful since it corrodes building materials such as marble or limestone, metals like iron, steel, aluminium etc.

The presence of SO₂ hampers the production of chlorophyll and the leaves turn colourless. This is known as chlorosis.

Control of SO₂ pollution:

• Removal of sulphur from fuel i.e., desulphurisation of fuel by using chemical scrubbers
• Use of fuel containing less amount of sulphur
• For example: Natural gas.
• Removal of SO₂ from gaseous fuels.
• Production of electricity in nuclear power plants instead of thermal powerplants

Sulphur Trioxide (SO₃)

1. Sources of SO₃

A significant amount of SO₂, emitted from natural sources or man-made processes is oxidised to sulphur trioxide (SO₃)

1. SO₃ molecules get activated by absorbing radiations having a wavelength of 300-400 run and react with aerial

SO₂ is also oxidised to SO₃ by ozone, hydrogen peroxide and oxides of nitrogen (NO_x) present in the atmosphere

 Harmful effects of SO₃:

SO₃ reacts with water vapour present in the atmosphere to yield sulphuric acid (H₂SO₄). Produced H₂SO₄ combines with water droplets present in air to form an aerosol and ultimately come down as acid rain.

Historical buildings For example:

Tajmahal, Victoria Memorial, monuments, sculptures etc., made up of limestone, marble etc., are adversely affected by

Acid rain*: CaCO₃+ H₂SO₄→ CaSO₄+H₂O + CO₂

Apart from these, metallic (aluminium and iron) structures, bridges, etc., are severely damaged by acid rain. Acid rain increases the acidity(i.e., decreases the pH level of ponds, lakes etc., and in consequence, aquatic plants and animals get dangerously affected.

Acid rain also decreases the stability and glossiness of paint and varnishes.

Sink of SO_x:

Edifices, historical memorials, monuments, and sculptures made of marble, limestone and natural sources of ammonia act as a sink of SO_x.

2. Oxides of nitrogen (NO_x)

Nitrogen forms five oxides—N₂O, NO,N₂O₃, NO₂ and N₂O₅. Out of these, NO and NO₂ act as chief air pollutants. NO and NO₂ are designated

Natural sources of NO_x:

1. During lightning discharge nitrogen and oxygen combine together to form nitric oxide (NO) and this nitric oxide on reaction with excess oxygen, produces nitrogen dioxide (NO₂ ).

N₂ + O₂ → 2NO ; 2NO + O₂ →2NO₂

2. Decomposition of ammonium salts in the soil by some bacteria leads to the formation of oxides of nitrogen (NOx), mainly NO.

Sources of NO_x created by human activities:

In thermal power plants and different industries, atmospheric N₂ and O₂ combine to produce large amounts of nitric oxide (NO). This NO reacts with aerial oxygen to give NO₂.

• The high temperature produced during the burning of fuels in petrol and diesel engines also favours the formation of NO by mutual interaction of atmospheric N₂ and O₂
• NO thus formed is subsequently converted to NO₂ by aerial O₂
• An abundant quantity of NO_x gas escapes into the atmosphere from industries producing organic acid.
• Atomic explosions also add to NO_x in the air.

Harmful effects of NO_x:

1. NO₂ gas is relatively toxic but its adverse effect depends on its concentration in the air and the extent of the reaction.

• Higher concentration of NO₂ in the air produces diseases like inflammation of the lungs, bronchitis, pneumonia etc.
• If NO₂ of higher concentration is inhaled, pulmonary oedema and haemorrhage of the lungs may occur.

2. The most harmful effect of NO_x in the atmosphere is the formation of photochemical smog.

• In the presence of sunlight, hydrogen, nitrogen dioxide and oxygen in the atmosphere, on reaction, gives a mixture of ozone, peroxyacyl nitrate (PAN) and aldehyde.
• All these substances unitedly form photochemical smog. Photochemical smog irritates the eyes and nose and induces sneezing, cough and difficulty in breathing (dyspnoea). If photochemical smog persists for a long period, it may cause death.

3. NO_x drastically reduces the rate of the photosynthesis of plants. Leaves and fruits start shedding due to the presence of NO_x in the air.

4. NO and NO₂ present in the atmosphere react with ozone to form NO₂ and NO₃ respectively. From the latter (z’.e., NO₂ and NO₃), N₂O₅ is obtained. N₂O₅ thus produced, on reaction with rainwater, forms nitric acid

NO +O₃→NO₂+ O₂ ; NO₂+ O₃→NO₃ + O₂

NO₂ + NO₃→N₂O₅; N₂O₅+ H₂O→2HNO

Sink of NOx:

In the atmosphere, the maximum stability of NO and NO₂ are of four days and three days respectively. After that, they are converted to nitric acid (HNO₃). This transformation may occur in two ways following path 1 and path 2 . Ozone plays a major role in the transformation occurred by Path 2

Nitric acid thus produced comes down during the rain. A part of it falls on waterbodies

For example: Ponds, rivers, lakes etc

The remaining part, on reaction with different basic Compounds belonging to hydrocarbon series (organic substances {e.g., ammonia, lime etc.) present in the soil, Is pollutants): The main air-polluting hydrocarbons are converted into nitrate salts. Here, water and the different basic materials in the soil work as the sink of NO_x.

Control of pollution caused by NO_x:

When the gas released from automobile engines is passed through a catalytic converter in the presence of Pt-catalyst, oxides of nitrogen (NO_x) are reduced to produce mainly N₂ and a small amount of NO₃.

Production of NO_x may be reduced by conducting the combustion at a lower temperature in the presence of excess air.

Before releasing the gas mixture containing NO_x, produced in the factories, it is passed over the metallic oxide catalyst

For example:  Cr₂O₃, ZnO, CuO etc.)

Heated to 500°C, thus nitric oxide (NO) is reduced to N₂ and O₂: 2NO ⇌ N₂ + O₂.

In the chemical absorption process, NO_x can be removed from the waste gas mixture. In this case,

1. Acidic For example H₂SO₄
2. Basic substances For example: Ca(OH)₂ or Mg(OH)₂ are used

3. Hydrogen sulphide (H₂S)

Natural sources:

• H₂S gas is liberated from volcanoes.
• Due to the decomposition of proteinaceous compounds containing sulphur, H₂S has evolved. Thus, rotten fish or eggs smell like H₂S gas.

Sources created by human activities:

• In oil refineries, during the production of paper and paints (containing sulphur) appreciable amount of H₂S is produced. Harmful effects of H₂S .’H₂S is a poisonous gas.
• It has severe harmful effects on man. It causes headache, nausea, irritation to the eyes, throat and nose, loss of appetite and diarrhoea.
• When taken in higher doses, it may lead to respiratory problems like bronchial pneumonia or even death.
• The reaction of H₂S with essential proteins is the primary cause of its toxic effects on human bodies. H₂S binds with iron in the mitochondrial cytochrome enzymes, thus preventing cellular respiration.

Sink of H₂S : H₂S undergoes slow oxidation to SO₂ in the atmosphere

2H₂ S + 3O₂→  2SO₂ + 2H₂O

H₂S + O₃ → SO₂ + H₂O

It also combines with various metallic salts to form insoluble metallic sulphides

4. Compounds belonging to the hydrocarbon series (organic pollutants)

The main air-polluting hydrocarbons are methane, benzene etc. Beiides thiete,
acetylene, ethylene, propylene, 1,3 butadiene etc., act as air pollutants. Among the gaseous air pollutants, the one which Is present In maximum quantity In air Is methane

Natural sources:

• In paddy fields and other muddy marshy lands, bacterial decomposition of plants, almost In the absence of air, produces plenty of methane.
• Putrefaction of animal excreta produces an abundant quantity of methane.
• The anaerobic decomposition of animal bodies produces methane.
• Forest fires and the evaporation of hydrocarbons of the terpenoid class from plants In forests are also important sources of hydrocarbon.

 Sources created by human activities:

• Hydrocarbons are produced due to the incomplete combustion or evaporation of the liquid fuels used in vehicles.
• Hydrocarbons also escape into the atmosphere as a result of incomplete combustion of fuels used for different purposes

For example: Cooking, lighting etc

• Liquid substances such as benzene, toluene etc., used as solvents in different chemical industrial units get easily evaporated and pollute the atmosphere
• Gaseous hydrocarbon, 1,3-butadiene used in the preparation of rubber and other polymers causes air pollution.
• During destructive distillation of coal, some air pollutants [e.g., benzopyrene) escape into the atmosphere.

Harmful effects of hydrocarbons: 

• Methane is a greenhouse gas.
• Due to photochemical reactions with oxygen and oxides of nitrogen, hydrocarbons form photochemical oxidants and photochemical smog, which are responsible for irritating eyes, nose and lungs and also cause breathing problems.
• Polycyclic aromatic hydrocarbons (PAH)
  • For example: Benzopyrene are carcinogenic and its presence in the atmosphere in large amounts may cause cancer.

Sink of hydrocarbon:

Hydrocarbons are sufficiently stable. However, they undergo slow oxidation or photochemical reactions involving several steps and ultimately form products like CO₂ or other water-soluble compounds which are then washed away by rain.

Control of pollution caused by hydrocarbons:

Since automobiles are the main sources of hydrocarbon pollution, so such pollution can be controlled by following those steps which are taken to control CO pollution.

Particulates

Generally, finely divided solid and liquid particles, suspended in air are referred to as particulates. The diameter of the particulates varies from 0.0002μ to 500μ (1 micron or 1 μ= 10^-4cm).

The particles of this dimension, being dispersed in air, form aerosol. Depending on the diameter, density of the particles and the intensity of air current, these particles exist in the atmosphere for a period ranging from a few seconds to a few months.

Particulates can be of two types:

• Viable (living microorganisms such as bacteria, viruses, fungi etc.) and
• Non-viable (non-living matters such as mist, smoke, dust etc.)

1. Suspended particulate matter

Smoke, soot, dust particles, metallic oxides and chlorides, fly ash, asbestos dust, acid mist(H₂SO₄, HNO₃)etc.

Natural sources of particulates:

Small particles on the surface of the earth are scattered into the atmosphere by air currents, cyclones, volcanic eruptions etc.

Sources created human activities:

• Soot:  These are fine carbon particles formed by incomplete combustion of carbonaceous fossil fuels.
• Metal particles: These are generated in the metal extraction involving processes like grinding, calcination, smelting of ores etc.
• Particles of metal oxides: During the combustion of fuels containing metal oxides, fine particles of metal oxides are generated.
• For example: Coke containing FeS₂, on combustion, produces fine particles of Fe₃O₄.

3FeS₂ + 8 O₂ → Fe₃O₄+ 6SO₂

• PbCI₂ and PbBr₂:  Compounds like tetraethyl lead (TEL), dichloroethane, dibromoethane etc., are used in petrol as anti-knocking agents. The Pb-compound during combustion of petrol produces PbO which later turns into volatile PbCl₂ and PbBr₂. These further escape into the air and exist as small particles.
• Inorganic silicates: Fine particles of silicates are scattered into the atmosphere from cement industries.
• Asbestos particles: Asbestos is a fibre-like silicate mineral. During the formation of the asbestos sheet, fine particles of asbestos arÿÿatteredinto the atmosphere.
• Sulphuric and nitric acid mist: The SO_x and NO_x  vapours present in the atmosphere react with water vapour and form their corresponding acid mists
• Particles of metal oxides: During the combustion of fuels containing metal oxides, fine particles of metal oxides are generated.
  • For example: Coke containing FeS₂, on combustion, produces fine particles of Fe₃O₄
• Organic particulates: These are mainly the particles of alkane, alkene and aromatic hydrocarbons
  • For example: PAH.
• The formation of such particles is associated with the combustion of petrol and petroleum refining. PAH particles get attached to the soots floating in the air easily and create severe health hazards.

2. Harmful effects Of particulates

The harmful effects of particulates depend on the particle size and the nature of the substances from which these particles originate. Generally, finer particles are more harmful. This is because, the particles with a diameter greater than 5μ get trapped in the nostril but particles having a diameter less than 5μ enter the lungs through the nostril.

The magnitude of the surface area of extremely fine particles being exceedingly high, carcinogenic particulates

For example:

Polycyclic aromatic hydrocarbons, asbestos etc.) can easily find their shelter on these particles and cause cancer, asthma, tuberculosis and different lung diseases. Apart from this, finely divided suspended particles in the air, enter the body through the eyes, ears, nose etc.,

Leads to different types of diseases:

• Smoke released from automobiles contains lead particles which adversely affect the child’s brains and cause nerve diseases.
• The normal production and development of red blood corpuscles (R.B.C.) are disturbed in the presence of lead particles. If an excess amount of lead particles are inhaled regularly, haemoglobin disintegrates and is eliminated through urine
•  Accumulation of cadmium particles in the body during respiration even in trace amounts, may cause breathing trouble and heart disease.
• Beryllium compounds
  • For example: BeCl₂, BeSO, ) affect the lung and create berylliosis disease.
• Workers of coal mines and cotton mills are prone to be attacked by diseases like black lung and white lung.
•  Workers of cement factories are susceptible to five attacks of silicosis due to the intake of SiO₂ particles during respiration.
• Inhalation of asbestos particles results in asbestosis and it leads to cancer in the case of workers of asbestos factories.
• The cause of arsenicosis is due to inhalation of arsenic compounds. In this disease, the skin becomes rough and wounds appear on the skin.

The harmful effects of particulates also extend to the plants present in the atmosphere react with the Water kingdom. Accumulation of dust and other particles on the vapours and their corresponding acid mists. leaves of plants close to the stomata. As a result, transpiration as well as photosynthesis of plants get severely affected. Naturally, the growth of plants and the production of crops also get depreciated

Ozone Layer

In the lower region of the stratosphere (the region at the height of 15 km to 35 km from the ground), there exists a layer of ozone gas. This layer is known as the ozone layer or ozonosphere.

Almost 90% of total ozone gas exists in this layer. In the absence of the ozonosphere, the existence of living beings would have been at stake. It is this ozone layer in the stratosphere which absorbs the harmful ultraviolet radiations coming from the sun. Thus it prevents most of the ultraviolet rays from reaching the Earth’s surface

1. Formation of the ozone layer

Oxygen molecules (O₂) present in the stratosphere absorb ultraviolet radiations coming from the sun and decompose to form oxygen atoms (O). This atomic oxygen combines with oxygen molecules to form ozone molecule

O*₃ + M → O₃ + *M [* Asterisk sign indicates excited state]

M  denotes a neutral colliding species

For example:

O₂ or N₂ with which O₂  on collision, releases its excess energy] On the other hand, the ozone molecule ( O₃  ) also absorbs UVradiation and gets converted into oxygen molecule ( O₂ )

In the ozone layer of the stratosphere, these two opposite processes (i.e., the formation of ozone molecule and the decomposition of ozone molecules) occur in a cyclic order and finally attain a state of equilibrium. Due to the existence of such an equilibrium state, the quantity of ozone in the stratosphere remains fixed.

2. Role of ozone layer in the environment

The ozone sphere works as a protective layer for the fitting world. Acting as a protective umbrella, the ozone layer absorbs most of the harmful UV radiation emitted by the sun because these rays are utilised in the production and decomposition of ozone.

In the absence of the ozone layer, the earth’s surface and the adjacent air would be so heated by the UV-radiation that the existence of the plants and the animals including bacteria in land and water would have been impossible.’

Ultraviolet radiation:

• Causes cancer in human skin
• Damages the cornea of the eyes and develops premature cataracts
• Decreases immunity against diseases and fertility in living beings. Genetic diseases are also the consequence of the harmful effects of ultraviolet radiation

3. Depletion of ozone layer: Ozone hole

In 1982, the British scientist Jo Foreman first observed that the ozone layer of the stratosphere above the Antarctic (the south polar regions) was gradually getting thinner. Extensive research in the subsequent years has revealed that the ozone layer is gradually becoming thinner not only in Antarctica but almost everywhere in the stratosphere. The phenomenon of thinning of the ozone layer of the stratosphere is known as depletion of the ozone layer or the ozone hole.

Depletion of the ozone layer signifies that the equilibrium between! the two contradictory’ Processes i.e., the formation and the decomposition of ozone has been disturbed somehow. Due to the influx of several foreign substances into the atmosphere, the rate of decomposition of ozone has far exceeded than the rate of its formation. This has resulted in the thinning of the ozone layer almost every where in the stratosphere

Ozone layer before formation of hole:

Ozone layer after formation of hole:

Causes of depletion of ozone layer (formation of ozone hole):

1. Scientists believe that some chemical substances belonging to the class of chlorofluorocarbons (Freons or CFCs) are mainly responsible for the formation of ozone hole. Chlorofluorocarbons (CFCs) are the different chloro and fluoro derivatives of methane and ethane.

Some examples of CFCs are given below:

The above-mentioned chemicals were extensively used as

• Refrigerants
• Propellants in aerosols,
• Foaming agent in plastic production,
• Ingredients of fire extinguisher,
• Solvents for various purposes etc. In the troposphere, these gases are non-corrosive, non-toxic, non-inflammable and chemically inert.

As a result, these gases after being liberated from the field of their applications, gradually reach the upper stratosphere after a long period of time.

In the stratosphere, they absorb the UV radiation coming from the sun and decompose to produce highly active chlorine atoms which subsequently with O₃ of the ozone layer to liberate oxygen and chlorine monoxide free radical (CIO) which, on further reaction with ozone, forms O₂ molecules and active chlorine atoms. The chlorine atoms again combine with O₃ molecules to form O₂ molecules. In this way, a cyclic process continues, which eventually causes depletion of the ozone layer.

It has been experimentally found that a single Cl -atom is capable of decomposing millions of O₃ molecules.

2. Experiments head revealed that halons widely damage the ozone layer. Halons are halocarbons. Most of them contain bromine as halogen. These are mainly used as fire extinguishers

For example: Halon—1211 (CF₂BrCl, bromochlorodifluoromethane),

Halon: 1301 (CF₃Br, bromotrifluoromethane) etc.

Halons are stable in the troposphere. But in the stratosphere, they absorb UV-radiations and decompose to produce active bromine atoms. These active bromine atoms combine with O₃ of the ozone layer to liberate oxygen and bromine monoxide free radical (BrO).

The produced BrO again reacts with ozone to evolve O₂ molecules and active bromine atoms. Bromine atoms thus obtained, in reaction with O₃, give O₂ molecule. In this way, the entire process proceeds continuously in a cyclic manner which leads to the decay of the ozone layer.

3. Extensive studies have unquestionably proved that increase in quantity of die oxides of nitrogen in the stratosphere adversely affect the ozone layer. The main source of these oxides are the supersonic aeroplanes which emit plenty of NO gas while flying through the stratosphere. Like Cl and Br-atoms, NO molecule brings about catalytic decomposition of O₃ into O₂

NO + O₃→NO₂ + O₂ ; NO₂ + O → NO + O₂

The reaction of O₃ with NO yields NO₂ yields. This NO₂ combines with the oxygen atom (which ”highways produced in the stratosphere due to the decomposition of O₃ and O₂ under the influence of UV-radiation) to regenerate NO. This explains why the O₃ molecules undergo continuous decomposition although the quantity of NO is not diminished.

4. Effect of ozone hole on the environment

Effect on climate:

If the ozone layer in the stratosphere is destroyed, the UV radiation emitted by the sun, instead of being absorbed by this region, will be incident on the earth’s surface. Consequently, the temperature of the earth’s surface will increase. Owing to this rise in temperature the earth will be continuously heated and the ice in the polar regions will melt, resulting in a rise in
the water level of the sea.

Effect on mankind:

In the absence of ozone layer in the stratosphere, the UV radiation will directly reach the earth’s surface. This radiation is extremely harmful to human beings. It causes skin cancer and premature cataract in the eyes. Exposure to the UV-radiation damages the immune system which thereby increases susceptibility to viral infections. Moreover, this radiation motivates the photochemical reactions which increases the tendency of smog formation. This in turn creates severe respiratory problems such as bronchitis, tracheal irritation, lung diseases etc.

Effect on plants, animals and other living organisms:

The incidence of UV radiation on the earth’s surface will hinder the process of photosynthesis. As a result, the production of crops will decrease. UV radiation would naturally increase the earth’s average surface temperature. Water bodies will dry up and water from the soil will evaporate. Consequently, agriculture will be greatly affected and the production of crops will fall drastically.

Also, UV radiation precludes photosynthesis. Therefore plants and aquatic phytoplanktons will die. Thus, marine life which depends on phytoplankton will also perish. Therefore, UV radiation disrupts the entire ecological system and composition of the sea

Greenhouse And Greenhouse Effect

1. What is a greenhouse?

Greenhouse means a glass room or glass chamber. Plants of the tropical region cannot adapt themselves to the climatic conditions of the cold countries. So for sustaining plant life (particularly for plants of tropical regions in cold countries), this type of chamber made of glass is used. Sun rays enter the glass chamber through the transparent glass roof and walls and due to this the soil gets heated.

The heated soil inside the chamber radiates infrared rays of longer wavelengths which cannot pass through the glass. The glass absorbs a part of these rays and the rest are reflected to the soil inside the chamber. As a result, the temperature inside the chamber always remains higher than that of the outside temperature. Thus, proper growth of these plants becomes possible.

In fact, some gaseous substances present in the earth’s atmosphere such as CO₂ water vapour etc., together act like a glass of the greenhouse and keep the atmosphere adjacent to the earth’s surface warmer and create a favourable environment for the living world.

2. Greenhouse effect and its importance

Greenhouse Effect Definition:

The natural process by which CO₂  water vapour and some other gases are present in the atmosphere, prevents the return of the radiation emitted by the earth’s surface to outer space, thereby keeping the surface of the earth and the adjacent environment suitable for the effect.

‘ Some gases like CO₂, water vapour etc., present in the atmosphere allow sun rays of smaller wavelengths to be incident on the earth’s surface but prevent the rays of longer wavelength (infrared rays) emitted from the hot earth’s surface, from returning to the outer space. Those gases absorb a significant portion of the reflected radiation of longer wavelength and arc heated.

The rest of the infrared rays fall on the earth’s surface and remain in the adjacent atmosphere to keep the surface of the earth and the adjacent atmosphere warm and make it favourable for the existence of the living world. due to indiscriminate deforestation, the quantity of CO₂ absorbed by the plants is gradually decreasing.

Greenhouse gases like CO₂, water vapour etc., help to keep the atmosphere warm to a certain level of temperature (average as 5°C) which is essential for the existence of life on earth. If those gases were not present in the atmosphere then the average temperature of the earth’s surface and that of the surrounding atmosphere would have dropped to about -30°C and eventually, survival of life on earth would have been impossible

3. Greenhouse gases, their sources and contribution towards the greenhouse effect

The gases that absorb a significant portion of radiation of longer wavelengths (infrared rays) emitted by the hot earth’s surface and reflect the rest to the earth’s surface, to keep the adjacent environment warm, are referred to as greenhouse gases. Some greenhouse gases are—carbon dioxide (CO₂), methane (CH₄), chlorofluorocarbon (CFCs), ozone (O₃), nitrous oxide (N20), water vapour (H₂O) etc.

1. Carbon dioxide:

Out of all the greenhouse gases, CO₂ is present in the largest amount in the atmosphere. Naturally, CO₂ plays the most vital role in absorbing the radiation emitted by the earth’s surface. The contribution of CO₂ towards the greenhouse effect is approximately 50%.

During respiration, plants and animals take in O₂ and give up CO₂  while plants accept CO₂ for the preparation of their food. In this way, the CO₂  -level in the environment is maintained. But at present, due to the progressive increase in the quantity of CO₂  in air, the equilibrium of CO₂  gas in the atmosphere has been disturbed. The possible reasons for the continuous

Increase in the percentage of COz gas are as follows:

1. 1.  Due to the indiscriminate use of fossil fuels in factories, motor vehicles etc., the quantity of CO₂ released in the atmosphere is not being used up completely by different natural processes.
2. Consequently, the concentration of CO in the atmosphere keeps on increasing.
3. In industrial regions, particularly during the manufacture of cement, a large &ftU>unt of CO₂ gas is released into the atmosphere.
4. During the process of photosynthesis, plants absorb CO₂ from the air. But due to indiscriminate deforestation, the quantity of CO₂ absorbed by the plants is gradually decreasing.

2.  Methane:

The role of methane gas in preventing the outflow of the heat emitted from the earth’s surface is worth mentioning. Due to the bacterial decomposition plants in paddy fields and other marshy lands, putrefaction of dung and other excreta and anaerobic decomposition of dead animals, methane gas is produced. Besides these, different waste organic compounds, oil mines etc., are the other sources of methane gas.

The capacity of each methane molecule to prevent the outflow of heat is 25 times a much as that of a molecule of CO₂  gas. But the quantity of methane gas in the atmosphere being less than that of CO₂ gas, its contribution to the greenhouse effect is about 16-20%.

3. Chlorofluorocarbons (CFCs):

CFCs are widely used as refrigerants, propellants in aerosol sprays, fire extinguishing agents, solvents for cleaning electronic types of equipment and foaming agents. These compounds destroy the ozone layer in the stratosphere and act as greenhouse gases in the troposphere.

The capacity of the chlorofluorocarbon molecules to prevent the release of heat emitted from the earth’s surface is 15000-20000 times greater than that of CO₂ molecules. These compounds are extremely stable. So, they can exist in the atmosphere for a long time. The contribution of these compounds towards the greenhouse effectis found to be 13-18%.

4. Tropospheric ozone:

Ozone gas present in the troposphere acts as a greenhouse gas. The combustion of fossil fuels in automobile engines, thermal power plants and different chemical industries gives rise to a profuse quantity of oxides of nitrogen (NO_x). The combination of ; different hydrocarbons and oxygen present in the atmosphere with these oxides results in the formation of ozone gas. The contribution of ozone gas to the greenhouse effect is about 7-8%.

5. Nitrous oxide:

Extensive combustion of fossil fuels, motor vehicles, and bacterial decomposition of nitrogenous chemical fertilisers in agricultural lands generates nitrous oxide. Again, its heat retention capacity per molecule is 200 times greater than that of CO₂ per molecule. The contribution of this gas towards the greenhouse effect is about 4-5%.

4. Global warming

For tire last few centuries, the average temperature of Tire Earth has been gradually increasing.

For example: During the period from 1800-1900 AD, the average temperature of the earth has increased by nearly 0.4°G. Again, in the following century i.e., 1900-2000 AD., this increase in temperature has been almost of 1°C. So it cannot be denied that the natural environment is gradually becoming warmer.

The phenomenon of this progressive rise in temperature all over the world is called global warming. The reason for this global warming can be attributed to the increased concentration of greenhouse gases in the atmosphere, caused by various human activities

Harmful effects of global warming: 

1. Because of global warming 2100 AD, the polar ice caps will melt, thereby releasing an enormous amount of water. Then the situation will be almost similar to what it was 1,30,000 years ago, when the surface water level of the sea was 6 years ago, when the surface water level of the sea was 6 coastal regions like Holland, America, New Orleans, Florida, Bangladesh etc., will be inundated and will go under water forever.

2. Global warming is a great threat to human health. Respiratory problems occur frequently due to human health.

Respiratory problems occur frequently due great concern. Global warning would initiate a favourable temperature for the breeding of microorganisms resulting in the epidemic spread of dreadful diseases such as dengue, malaria, encephalitis etc. If the CO₂ content in the air becomes twice that of the present value, then many species will become extinct from the earth

5. Consequences of the greenhouse effect

Scientists have predicted about the effect of increased concentration of greenhouse gases such as

• The temperature of the earth’s surface and the troposphere will go to increase day by day and by the middle of this century, the temperature of the earth will be increased by at least of 2°-4°C.
• Due to the increase in earth’s temperature, the polar caps, accumulated in tyre polar regions (Greenland and Antarctica) will melt and this will cause an increase in the water level of the sea. As a consequence, vast coastal regions like India, Bangladesh, Myanmar, Maldives etc., will sink, causing colossal devastation. If the populated area be inundated in this way, the resettlement of the affected people will pose a great problem to many countries
• Owing to the increased greenhouse effect, droughts will be more frequent during summer in the countries of the mid¬ latitudes in the northern hemisphere. As a result, crop production in the fertile lands of North America and the previous Soviet Russia will be reduced.
• More devastating cyclones, supercyclones, tornados or hurricanes will occur with an increase in temperature.
• Increase in temperature may lead to the destruction of forests due to forest fires.
• Due to the inability to sustain at high temperatures, living beings will die. Consequently, the ecosystem will be severely affected. In the marshy lands, due to increased decomposition of plants, methane will be liberated.

In a word, it can be said that by the middle of this century, man will have to face severe natural calamities.

6. Measures to check global warming

Global warming cannot be eradicated or reduced overnight. A concerted effort is necessary to attain this goal. In overnight. A concerted effort is necessary to attain this goal.

In measures are mentioned below:

• The addition of CO₂ to the atmosphere should be minimised by reducing the use of fossil fuels such as wood, coal, petroleum etc.
• Unlawful cutting of trees should be stopped and the forests should be saved from destruction.
• Afforestation ought to be encouraged so that plants absorb more CO₂ (for the preparation of their food). Koiget !r ’Boron
• Use of unconventional forms of energy
• For example: Solar energy, wind energy, tidal energy etc.) is to be increased.
• Use of CFCs is to be prohibited

Smog Or Classical Smog

In December 1952, the city of London was covered with a dense layer of fog continuously for five days. The people, irrespective of age and sex, fell ill and 4000 people ultimately lost their lives.

Subsequently, it was found that the fog contained poisonous gases emitted from automobile engines and factories and the constituent which was present in the largest quantity, was found to be sulphur dioxide gas (SO₂). A British physician named it smog (smog = smoke + fog). As the horrible effect of such smog was first observed in London, it was called London smog

Several accidents caused by such smog (of course of less alarming proportions), occurred in different cities. Smog is frequently observed in big cities

For example:

Delhi, Mumbai Kolkata) of India, during the winter season. Mixture of particulates with gaseous oxides of Mixture of particulates with gaseous oxides of the presence of SO₂ and carbon (soot) particles, classical smog possesses a reducing character. Thus it is also called reducing smog

1. Formation of smog

During winter, particularly after evening or early in the During winter, particularly after evening or early in the earth’s surface becomes heavier If it is suddenly cooled down earth’s surface becomes heavier ifit is suddenly cooled down cannot go upwards and remains confined in that layer. Impure cannot go upwards and remains confined in that layer. Impure finely divided particles liberated from local factories motor vehicles, mix with that confined air to create finely divided particles liberated from local factories motor vehicles, mix with that confined air to create and and

Harmful effects of smog:

• Smog irritates the nose, eyes and throat, resulting in sneezing and coughing.
• It affects the respiratory system, causing bronchitis, asthma, heart disease etc.
• It lowers visibility level, posing great problems while driving cars. So, accidents are likely to happen.
• It also has adverse effects on electronic systems and plants

2. Photochemical smog or Los Angeles smog

This type of smog was first observed in the city of Los Angeles in America, in the year 1950. So, it is called Los Angeles smog. Highly poisonous substances like nitrogen dioxide(NO₂) and ozone (O₃). peroxyacyl nitrate (PAN), smog was formed due to chemical reactions in the presence of bright sunlight, it is commonly known as photochemical smog. Generally, during the mid-days of the summer when the sun shines brightly, (i.e., the intensity of solar radiation is very high) this kind of smog is observed

In big cities, where there is considerable vehicular traffic on the roads throughout the whole day and night, the atmosphere contains the oxides of nitrogen particularly, nitrogen dioxide (NO₂) in the largest proportions.

Apart from these, hydrocarbons (produced by evaporation or incomplete combustion of liquid fuels) and other gaseous substances

For example: SO₂> CO₂  are present.

In the presence of bright substances like ozone (O₃), peroxyacyl nitrate (RCO₃NO₂), aldehyde and ketone. These gaseous substances and the particulates mix together in the air to form photochemical smog.

It formation of smog is to be noted that, it is not real smog, because it contains particulates mix in air to form photochemical smog. The formation of smog is to be noted that, it is not a real smog, because it contains Hence it is also known as oxidising smog

Mechanism for the formation of photochemical smog:

In the presence of sunlight, nitrogen dioxide (NO₂) molecule decomposes into nitric oxide (NO) molecules and atomic oxygen

In the reaction of hydrocarbons with this atomic oxygen, at first highly reactive free radical RCO is produced and this radical again combines with oxygen molecule to give peroxyacetyl radical

Peroxyacyl radical is highly reactive. It combines with hydrocarbon,O₂ and XO₂ to form a mixture of aldehyde, ketone, ozone and peroxyacyl nitrate respectively. This peroxyacylnitrate is extremely harmful for eyes.

Harmful effects of photochemical smog:

• Presence of large amounts of ozone (O₃), peroxyacetyl nitrate (PAN), acetaldehyde, ketone etc., causes
  • Irritation of eyes, nose, and throat but it sill effect on the eyes is much more intense
  • Congestion of nostrils, sneezing and cough
  • Respiratory problems and chest pain.
• By brown colour, it reduces visibility and hence the car drivers and pilots face extreme difficulties.
• PAN and other oxidising materials damage plant cells and produce white spots on leaves.
• PAN hinders the process of photosynthesis.
• Rubber goods lose elastic properties and become brittle.

To control or suppress the formation of photochemical smog, the following methods can be adopted.

• Certain chemical compounds, which are capable of generating free radicals, are sprayed into the atmosphere. The free radicals readily combine with the free radicals responsible for the formation of photochemical smog (such as O^•, R^•, R^•O, ^•H etc.) and hence nullify their effects.
• Efficient catalytic converters are being developed for installation in automobiles so that emission of nitrogen oxides and hydrocarbons can be prevented or minimized

Certain plants such as Pinus, Juniperus, Pyrus, Vritis etc., can directly assimilate oxides of nitrogen for their metabolic activity. So their plantation could be helpful.

Comparison between ordinary smog and photochemical smog:

Acid Rain

Ordinary water is slightly acidic (pH = 5.6) because a portion of carbon dioxide gas present in the air gets dissolved in water and forms carbonic acid

CO₂ + H₂O→H₂CO₃ .

But if rainwater contains an excess amount of dissolved acid, then it is called acid rain. Acid rain is mainly a mixture of H₂SO₄, HNO₃ and HCl. The pH of such rainwater generally lies within the range of 5.6 to 3.5. The proportion of the above acids in the rainwater of different localities depends upon the quantities of sulphur dioxide (SO₂), nitrogen oxides (NO_x) and hydrogen chloride (HCl) present in the air of that particular locality

1. Origin of Acid Rain

Huge quantities of the oxides of sulphur, nitrogen and carbon (SO_x, NO_x, CO_x etc.) are released In the air due to natural processes as well as tyre human activities. These oxides combine with oxygen, ozone and water vapour present in air to give different acids. These acids float in the air in the form of fine particles as an aerosol. Moreover, HCl gas is also liberated in sufficient quantity from the factories. These acids come down to the earth through dew, snow and rainfall

H₂SO₄ has the highest contribution (60-65%) to acid rain followed by HNO₃ having 30-35% contribution.

2. Harmful effects of acid rain

Effect on soil and plants:

Acid rain increases the acidity of the soil, changes the solubility of different metals and metallic oxides present in the soil. Thus, living creatures and bacteria living inside the soil are severely affected or die. As a result, the fertility of the soil decreases and the production of crops Is drastically reduced. Due to increased acidity of the soil, leaf pigments get spoiled, the process of photosynthesis and as a consequence the growth of plants and their immunity drastically fall, i.e., agricultural productivity is reduced.

Effect on aquatic plants and animals:

Due to acid rain, the pH of different water bodies decreases significantly. As a result, the production of spawn of fish is reduced. The biological processes of fishes are affected. An increase in acidity results in the elimination of many species of algae and zooplankton, aquatic insects, fishes etc. That is, polluted water disrupts the aquatic food chains and consequently disturbs the ecosystem. In countries like America, Sweden etc., in a large number of lakes, virtually no fish exists due to acid rain.

Effect on mankind:

Acid rain dissolves different metallic substances. These dissolved substances enter human bodies through water and result in severe health hazards. Acid rain has profound ill effects on human skin, hair and cells. H₂SO₄ and HNO₃ present in acid rain enter the human body and adversely affect the nervous, respiratory and digestive systems.

 Effect on architecture and edifice:

Because of acid rain buildings, monuments of historical importance

For example:

Tajmahal, Victoria Memorial, British Parliament House), states, sculptures etc., made of marble;, limestone, dolomite, mortar and slate suffer irreparable damages

Marble, limestone etc., react with H₂SO₄ to form an insoluble layer of CaSO₄ and lose its glossiness

CaCO₃+ H₂SO₄ → CaSO₄ ↓+ CO₂↑ + H₂O

Few years ago, scars developed on the surface of Tajmahal Few years ago, scars developed on the surface ofTajmahal Few years ago, scars developed on the surface of Tajmahal

Slone cancer:

• The scars that are developed on the surface of architectural edifices, memorials, sculptures etc., are termed stone leprosy or stone cance
• Metallic surfaces,
  • For example: Aluminium, steel or iron structures, bridges etc., exposed to acid rain, suffer steady.
• Textile materials, leather and paper products are also not spared from the ill effects of acid rain

3. Measures to check acid rain

Only the drastic reduction in the quantities of SOx and NOx in the environment can eliminate the apprehension rather than the threat of acid rain.

The following measures can be adopted to check acid rain:

Use of fossil fuels is to be decreased as far as practicable. Fuels of low sulphur content should be used so that the emission of SO₂ can be controlled.

Suitable technological devices should be developed for the removal of those gases

For example: SO_x, NO_x etc.)

Released from the thermal plants, factories, furnaces for metal extraction and various other sources

Vehicles involving engines with improved technology must be launched so that the emission of NO_x can be controlled

Water Pollution

In nature, water is an indispensable component. 97% of the In the nature, water is an indispensable component—97% of the water, which is practically of no use to human beings.

• The remaining 3% is sweet water, of which 2% remains in condensed form in polar regions and in various permanent glaciers.
• The remaining 1% of sweet water, which is accumulated in rivers, fountains, lakes, ponds, under the soil etc., is consumed for different useful purposes.
• Due to the polar nature of water, a large number of inorganic salts get dissolved in it. As a result, these salts become easily available to living beings.
• These salts are extremely important to aquatic life.
• The various gaseous pollutants such as CO₂, SO_x, NO_x etc., present in the atmosphere and organic and inorganic pollutants on the earth’s surface are swept by rainwater and mix with the rivers, lakes, seas etc.
• Due to different chemical reactions in water, these pollutants decompose to give unpolluted water. As a result, the extent of environmental pollution decreases.

Water pollution:

When the water of different water bodies gets contaminated with one or more chemical substances, evolved either by natural phenomena or indiscriminate human activities and tend to cause health hazards to man and other living beings or adversely affect the processes of their livelihood, then the water is said to be polluted.

1. Domestic wastes

Solid waste of various materials of domestic use

For example: Discarded paper, plastics, torn cloth, vegetable refuse, remains of food etc.),

Excreta of man and domestic animals are mostly left in open places. With time, these discarded materials are carried by wind or rainwater to the nearby water bodies. This contaminates the water and makes it unfit for use.

Water pollution caused by domestic wastes:

1. Domestic wastes mostly contain organic compounds. These organic compounds are decomposed by bacteria in the presence of dissolved oxygen (DO). This process is called biodegradation.

In the process of biodegradation, carbon, hydrogen, nitrogen, phosphorus etc., present in the organic compounds are oxidised to CO₂, H₂O, nitrate, phosphate and other salts. During the process the quantity of dissolved oxygen gradually decreases. Naturally, aquatic plants, fi hes and other aquatic organisms do not get sufficient oxygen for respiration.

Consequently, aquatic living beings face serious problems. DO is considered to be an important parameter in predicting the quality of water. For aquatic plants and animals, the value of DO must not be less than of 4-6mg L^-1 . With the increasing value of DO, the quality of the water gradually improves. Lowering the value of DO indicates that the water is getting polluted.

Biochemical Oxygen Demand or BOD:

Biochemical oxygen demand (BOD) may be defined as the number of milligrams of oxygen required for biodegradation (i.e., biochemical degradation) of organic matter present per litre of polluted water.

• For the determination of the BOD of a sample of water, the sample of water, kept at 20°C, is saturated with oxygen & is subjected to biodegradation (i.e., oxidation) of organic compounds for 5 days by the bacteria present in that water.
• The statement, the BOD of a sample of water is 60 or 60 mg.L^-1   means for the biochemical decomposition of organic matter present per litre of water, 60mg of oxygen is required. BOD of the sample of water, if expressed in ppm (parts per million), also gives the same value.
• Greater the value of BOD of water, the higher will be the extent of pollution of that water because if the water contains a large amount of organic matter, the quantity of oxygen required will be high.
• If the value of BOD of a certain sample of water is greater than 5 ppm then, the water is considered to be impure.

Chemical Oxygen Demand or COD :

• Water may sometimes contain organic or inorganic pollutants which are not decomposed by bacteria. These are called nonbiodegradable pollutants.
• So, the value of the BOD of any sample of polluted water does not truly reflect the extent of pollution of that sample of water. Thus, for the determination of the total quantity of biodegradable and non-biodegradable pollutants in a sample of water, the sample of water is oxidised by a strong oxidising agent (K₂Cr₂O₇+ H₂SO₄) in the laboratory.
• In this case, the oxidising agents supply the necessary oxygen required for the complete oxidation of the pollutants.
• The total amount of oxygen required for the complete oxidation of biodegradable and non-biodegradable pollutants is called Chemical Oxygen Demand (COD). Naturally, the value of COD of any sample of water is always greater than that of BOD.

2. If dissolved oxygen is deficient in water the oxidation of organic pollutants does not get completed. As a consequence of incomplete oxidation, methane (CH₄), hydrogen sulphide (H₂S), phosphine (PH₃), different amino compounds etc., are formed which creates an extremely off ensive odour.

3. Waste materials, sewage from dispensaries, hospitals and domestic wastes carrying pathogenic microorganisms are drained into the water bodies which may result in various diseases such as cholera, typhoid, paratyphoid, dysentery, hepatitis, polio, gastroenteritis, jaundice etc.

4. Waste materials like plastics do not undergo bacterial decomposition in the presence of oxygen, i.e., they are nonbiodegradable. They remain unaffected even if they areleft in water for years. Thus, they decrease the depth of water as well as increase the extent of water pollution under the influence of their constituent chemical compounds

2. Industrial wastes

• Industries release wastes, due to the production of organic and inorganic materials. Factories producing or using mineral acids like HCl, H₂SO₄, HNO₃, H₃PO₄etc., and alkalis
  • For example: NaOH, KOH, and NH₃ give up profuse quantities of waste materials or effluents which are thrown directly into the water of rivers, lakes, ponds etc.
• These acids or alkalis get mixed with water and increase the acidity or alkalinity of water.
• Again, the industrial wastes of different factories, containing metallic elements
  • For example: Pb, Hg, Cd, Zn, Cr, Mn, As, Be etc.)  mixes with different water bodies
• These metals have profound ill effects on aquatic plants and animals in particular.
• Direct use of this polluted water entails attack by several diseases.
• Besides, these metals, accumulated in human bodies through food chains, cause a wide range of diseases

1. Cadmium (cd):

Refining of zinc, copper and lead, electro¬ plating industries, iron and steel factories, Ni-Cd battery factories etc., release cadmium as waste material into rivers and other water reservoirs.

Harmful effects:

Cadmium, introduced into the body through water pollution causes vomiting, irritation of the lungs, malfunctioning of the liver and kidney high blood pressure, anaemia, disorder of bone marrow etc.

Ital-llai disease:

• In 1970, a disease caused by pollution due to cadmium occurred in Toyama Japan and came to be known as Itnl-Itai. The water containing cadmium discharged from a zinc extraction factory situated in that locality was used for irrigation.
• As a result, cadmium was incorporated into rice because of the cultivation of paddy with this polluted water.
• Cadmium was thus introduced into human bodies through this rice when consumed as food. Thus the disease Itai-Itai originated. Pain in bone and joints, weakening or brittleness Of the bone etc., are the symptoms of this disease.

2. Mercury (Hg):

The water discharged as industrial waste from the factories producing caustic soda, chlorine, pesticides etc., is die source of mercury pollution.

Harmful effects:

Mercury is highly toxic. It causes stomach pain, dropsy (oedema), headache etc. Moreover affects the nervous system and kidneys, decreases the reproductive power of males, and babies are found to be born with deformity.

Minamata disease:

In 1953-69, die disease caused by pollution due to mercury appeared in the Minamata area on the sea-coast of Japan and came to be known as Minamata disease. In that area, more than 100 people died of this disease and thousands of people became crippled. In this coastal region, waste materials contaminated with mercury from a polyvinyl factory were regularly discharged into sea¬ water.

Mercury present in the effluent was converted into highly poisonous methyl mercury by different reactions. This poisonous compound was introduced into human bodies through sea fishes and led to the outbreak of Minamata disease. The primary symptoms of this disease are the lack of sensation in muscles, lips, tongue etc., which culminate in blindness and loss of memory

3. Lead (Pb):

The waste materials discharged from factories For example:  extraction and refining of lead, paints, varnishes, alloys, batteries and ship-building etc.), containing lead, pollute the water of rivers, lakes and other sources. Apart from these, the anti-knocking compound [Pb(C₂H₅)₄] used in gasoline and petrol is a potential source of lead

Harmful effects:

If water contaminated with lead enters the body, lead gets accumulates in the body. Most of the lead is ultimately deposited in the bone. Lead poisoning gives rise to symptoms such as loss of appetite, vomiting, constipation, anaemia, insomnia, headache etc., and also affects the digestive system.

4. Manganese (Mn):

Effluents containing Mn from ferromanganese producing industries, welding factories and MnO₂ as waste materials released from dry batteries, mix with water as pollutants.

Harmful effects:

If Mn-containing water is consumed for a prolonged time, it causes nervous disorder.

5. Coball (Co):

Industrial discharge from ceramic, paint or dye industries results in the Co-pollution of water.

Harmful effects: If cobalt-contaminated water is consumed, symptoms such as lowering of blood pressure, diarrhoea, deformation of bones etc., are developed.

6. Arsenic (As):

The main sources of arsenic poisoning are pesticides, chemical wastes, pharmaceutical industries, mining by-products etc. In the tube well water in some places, arsenic compounds are present.

Harmful effects:

Water polluted by arsenic disturbs blood circulation in the skin and black or ash spots appear on the skin of the throat, neck and back. The skin of the hands and legs becomes rough and spots like moles appear on the skin. Continuous use of water containing arsenic for a longer time causes cirrhosis of the liver, cancer in the lungs and urinary track

7. Arsenic pollution:

According to the recommendations of the World Health Organisation (WHO), water containing 0.01 mg of arsenic per litre is quite safe for drinking. The limit of arsenic in water that human bodies can sustain is 0.05 mg L^-1. But the average arsenic content in the tube well water of some places in the vast region of Bangladesh including some districts of Gangetic West Bengal

For example:

North and South 24-Parganas, Nadia, Murshidabad, Maldah etc.) is 0.25mg. L^-1 . As a result of the indiscriminate use of this water, nearly ten lakhs of people have been victimised in West Bengal. Out of these, at least two lakhs of people have been suffering from acute skin diseases

8. Black-foot disease:

Consumption of arsenic contaminated for a long period also causes severe damage to. lower limbs and formation of black lumps on palm and foots. This is known as ‘black-foot disease.

3. Fertilisers used in agriculture

Chemical fertilisers or nutrients are extensively used for increasing the agricultural production. Mainly urea or organic fertilizers and ammonium sulphate, ammonium nitrate, monocalcium phosphate etc., are used as inorganic fertilisers. A certain portion of these fertilisers remains unutilised and being carried by the rainwater, falls into the nearby, lakes etc., and thus causes water pollution

Water containing nitrate ions cannot be used as potable water because nitrate ion cannot be removed by the usual process of purification of water. Consumption of such water affects the haemoglobin of babies, causing the disease called ‘blue baby syndrome’. Moreover, nitrate ions are converted to carcinogenic nitrosamines inside the body

Eutrophication: 

• Inorganic fertilizers or nutrients
  • For example: Nitrates, phosphates, sulphates etc.)
• Left unutilised in agricultural production, mix with water as waste materials and act as pollutants of the water.
• But, these materials enrich that water with nutrients and help in the rapid growth population of the aquatic plants.
• This higher rate of growth is found to be remarkably high in the case of algae.
• This phenomenon of enrichment of water mixed with fertilizers, causing rapid growth of the population of aquatic plants is called eutrophication.

The ill effects of this over-nutrition i.e., eutrophication may be summarised as:

• The aquatic plants, because of their rapid growth require abundant quantity of oxygen and cause depletion of dissolved oxygen (DO), thereby threatening the survival of aquatic life.
• When the quantity of dissolved oxygen decreases, the anaerobic bacteria grow abnormally and these bacteria react with those waste materials to form different gaseous substances such as methane, ammonia, hydrogen sulphide etc. As aresult, foul smell is emitted.
• With time when the plants die, the remains of the dead plants get deposited at the bottom of lakes, ponds etc., and become shallow.
• In extreme instances of eutrophication, when the population of plants explodes, they exhaust almost the whole of the dissolved oxygen. Consequently, fishes, insects and other aquatic animals die due to the absence of oxygen.

4. Pesticides used in agriculture

A wide range of synthetic organic chemicals are used for the better production and preservation of crops. For example, insecticides, fungicides, herbicides etc., are applied to the field to kill insects, fungi, herbs etc. These chemicals are collectively known as pesticides. Pesticides, when used in agricultural fields, are carried by flowing water. Thus, they enter the hydrosphere and cause pollution of water. Again, when pesticides are sprayed in the field, a part of them get mixed with the atmosphere which come down along with rain water and mixes with the water of the rivers, lakes etc. Water pollution is also caused by the wastes discharged from the factories producing pesticides.

Different classes of pesticides and their harmful effects:

Biomagnification:

There are some pollutants which do no There are some pollutants which do no aldrin, heptachlor etc. These compounds exist for years together, keeping their poisonous effect Intact. These are called permanent organic pollutants.

They are not soluble in water but soluble in fats and oils. So they dissolve in body fats and go on accumulating. These highly toxic substances accumulated in living bodies are transmitted to the bodies of other living beings through food chains. These persistent organic pollutants (POP) exist at highly toxic levels in the bodies of living beings owing to repeated consumption of polluted food

5. Detergent

Detergent is widely used as a cleaning agent in household work and in industry. The effluent released after its use mixes with the nearby ponds, rivers etc., and causes water pollution. Two chief constituents of detergent are—

• Surface active agent: For example: Alkylbenzene sulphonate (ABS).
• Builder of filler: For example sodium Yripolyphosphate [Na₅P₃O₁₀],if>Both these constituents are responsible for water pollution

Water pollution caused by surface active agents:

1. Surface active agents decrease the surface tension of water and consequently help in the formation of foam emulsion and oily substances with water. These surface active agents are non-biodegradable and thereby entail water pollution.

2. Foam created by detergents forms a layer on the surface of water and thus prevents water from coming in contact with air and sun rays. Consequently, water cannot absorb oxygen from air and the dissolved oxygen level (DO) in water decreases.

3. Furthermore, sun rays being obstructed, the aquatic plants at the bottom cannot release oxygen by the process of photosynthesis. For this reason, also, the dissolved oxygen level gradually gets diminished. This results in the deficiency of oxygen required for the respiration of aquatic plants and animals.

4.. Surface active agents form a layer on some organic pollutants

For example Phenolic compounds

So, phenolic compounds present in water can no longer come in contact with bacteria and hence the biodegradation of organic pollutants becomes inhibited. Consequently, the extent of pollution in water increases.

Pollution caused by builders or fillers

Detergent contains phosphate salts known as builders or fillers. Phosphate ions produced from them form water-soluble complexes by combination with the basic radicals Ca⁺², Mg⁺² etc. Iff These complex phosphate salts serve as nutrients for algae and aquatic plants, consequently affecting their rapid population growth (Eutrophication). Plenty of oxygen is required for their respiration. This results in rapid decrease in the level of dissolved oxygen (DO) and the survival of aquatic animals becomes extremely difficult.

6. Radioactive substances

Radioactive substances, during mining and refining as well as from nuclear power plants, may be carried into water. Radioactive discharges from medical and scientific institutions using radioactive isotopes may also lead to water pollution.

Harmful effects:

The presence of radioactive substances in trace amounts may cause nervous debility, physical deformity, miscarriage, sterility, cancer, blindness etc. The harmful influence of this radioactivity continues from one generation to another.

7. Thermal pollution

In hydroelectric power plants, generally, the water from rivers or lakes is converted into superheated steam which is used to rotate the turbine. Only a negligible fraction of heat carried by steam is transformed into electrical energy and the rest returns to rivers or lakes with the help of water. This process continues, in cyclic order.

As a result, the temperature of water of the river or the lake rises considerably and the dissolved oxygen (DO) level decreases, causing great harm to the aquatic animals, particularly the fishes. In thermal nuclear power plants and many other industries, water is used as a coolant, which is discharged at a high temperature to rivers or lakes resulting in a rise in the temperature of the water. This increased temperature accelerates the faster assimilation of the waste materials, causing the depletion of dissolved oxygen (DO).

8. Oil-slicks on sea-water

Mineral oils and by-products of oil spread into seawater for several reasons. Consequently, a layer of floating oil (oil slicks) on sea-water is formed and the transfer of atmospheric biochemical level oxygen dissolved of into dissolved oxygen decomposes sea-water(DO)oxygen levels is prevented reduced

• Again, from which further water oxygen in and Naturally required hence reduces this brings about a shortfall of oxygen required for respiration aquatic plants and animals and their survival becomes extremely difficult
• Moreover, oil-slicks on seawater do not allow sun rays to Moreover, oil-slicks on seawater do not allow sun rays to photochemical reactions of aquatic plants are hindered and their growth is remarkably inhibited thereby.
• At sea, the oil layer causes the death of birds. The oil floating on the sea penetrates through the feathers and wings of birds and thus their insulation and buoyancy are adversely affected. Consequently, their body temperature decreases and ultimately they die. This phenomenon is called hypothermia

9. Controls of water pollution

• Septic tanks should be used in every house.
• Bathing and washing of clothes in water bodies like ponds, lakes, rivers etc., should be controlled.
• Application of chemical fertilisers and pesticides must be done within a safe limit.
• Water from sewage systems has to be treated properly.
• Effluents from the industries should not be released directly to the water bodies before proper treatment.
• Oil leakages from oil-loaded ships must be stopped to avoid water pollution.

Soil

Soil is a constantly changing mixture of materials composed of organic and inorganic substances water air microorganisms etc., which allows plants to grow. Various kinds of organic and inorganic materials, mixed with ground are extremely difficult. rocks, give rise to the formation of soil.

 Chemical composition of soil:

Soil is a complex substance. Its various constituents are:

1. Minerals:

Soil contains different kinds of minerals. The chemical nature of the rock from which the soil originates determines the variety and quantity of minerals in it. The particles present in the soil are basically silicate minerals. The chief constituent elements of soil are silicon, calcium, sodium, potassium, magnesium, iron, aluminium, oxygen etc. These elements are present in the form of silica (SiO₂), silicate (KAISi308, NaAlSi308), epidote [4CaO, 3(AlFe)₂O₃, 6SiO₂, HO₂] etc.

2. Air:

The particles of soil leave enough space in between, which is occupied by air. The air present in the soil contains carbon dioxide, oxygen, nitrogen and water vapour. But the quantity of O₂ present in the soil is less than that of O₂ present in air while the quantity of CO₂ in the soil is comparatively greater than the corresponding amount in air.

3. Water:

Water content in the soil always varies from place to place. The constitution of soil determines its water tension capacity. If the amount of organic compounds present in the soil is increased then the water-retention capacity of soil will also increase. This water serves as a solvent for mineral and organic matter. Moreover, water retained in the soil plays a vital role in maintaining the structural arrangement of the soil.

4. Organic compounds:

Generally, organic substances are produced from the remnants of dead plant and animal bodies. Besides this, the waste material of living beings is also a potential source of organic substances. The organic matter liberated due to the bacterial decomposition of the remains of plant and animal bodies mix with soil to form humus. This humus is a very significant part of the soil.

Some of its qualitative features are:

• It holds particles of soil in a state of aggregation.
• It increases the water retention capacity of the soil.
• The movement of water and air inside the soil is enhanced by it.
• It serves as a source of food for the microorganisms present in the soil.

Effect of soil on the environment:

• The role of soil in the existence of life is very significant.
• Without soil, the evolution of plants and animals on land would not have been possible. If igneous rocks were heated by the scorching rays of the sun, then the environment would have been inimical to life.
• It is the layer of wet soil that makes the existence of life possible.
• Plants produce organic food by taking the required water and salt;

For example:

Sodium chloride from the soil. The animal kingdom survives by taking this organic food, otherwise, the existence of animal life would have been endangered. So, soil is a component of immense importance for the living world i.e., the flora and fauna

Soil Pollution

Soil pollution is caused when industrial wastes, radioactive pollutants, domestic and municipal wastes, and agricultural pollutants, are either thrown or dumped into the soil. These reduce the overall quality of soil and are harmful for living beings.

1. Various sources of soil pollution:

1. Pollution caused by industrial waste:

Plastic and paint industries, coal and mining industries, metallurgical units and the industries for the production of sugar, leather, cotton, pesticides, glass, cement etc., discharge a large amount of their discarded waste, which causes soil pollution.

• Moreover, the waste released by thermal and nuclear power plants also pollutes the soil
•  Industrial waste containing heavy metals is retained by the soil and these metals, on being absorbed by plants, enter into the human bodies through the food grains and display their toxic effect.
• Industrial effluents such as mercury, lead, zinc, arsenic etc., even destroy many bacteria which are useful for soil.

2. Pollution caused by municipal waste disposal:

Waste material discharged by municipalities

• For example:  Plastics, accumulated garbage in dustb, broken glasses, waste cloth pieces, paper, ash and other discarded materials) are dumped on the roadside or at some particular places.
• These waste materials not only pollute the soil but also act as breeding centres for pathogenic germs.

3. Pollution caused by fertiliser:

• Nowadays for agricultural production, chemical fertilisers are widely used. As a result of this indiscriminate use of fertilisers
• The microorganisms which produce humus and nutrients are set to face odds threatening their very existence.
• Use of excessive potassium-containing fertilisers decreases the vitamin-C content (ascorbic acid) in vegetables and fruits, indispensable for our health.
• Due to the application of superphosphate. Assimilation of copper, zinc etc., by the plants becomes very difficult.

4. Pollutionbypesticides:

• The chemical substances used to protect plants from the harmful effects of germs, insects, weeds, fungi etc., are called pesticides.
• Pesticides of various types are used to increase the production of crops. Pesticides are of three types, viz., insecticides, fungicides and herbicides.

The harmful effects of these pesticides are as follows:

• Use of excessive insecticides causes pollution of the soil. Insecticides belonging to the class of organophosphates weaken the muscles of animals. Chlorinated pesticides affect the nervous system and cause stomach cancer.
• Fungicides which destroy fungi are mainly compounds of mercury and copper. Extensive application of these compounds brings about severe soil pollution and disturbs the natural ecosystem.
• Herbicides destroy the unwanted weeds or herbs etc., grown in the soil. When these substances are used in excess amounts, they pollute the soil. In females, these interfere with reproduction and harm the foetus or result in the birth of crippled newborn babies.

5. Pollution caused by acid rain:

• In industrial areas due to air pollution, air becomes enriched with oxides of sulphur and nitrogen (SO₂ and NO₂ Which ultimately result in acid rain.
• Acid rain increases the acidity of the soil and adversely affects the cultivation of crops.

Pollution caused by radioactive substances:

Radio¬ active waste materials, emitted from atomic reactors, as a result of experimental studies on atom bombs and nuclear experiments, are added to the soil. The radioactive emissions from the waste pollute the whole environment including the land mass.

2. Controls of soil pollution

• Use of sanitary landfills i.e., where untreated waste is buried in layers and covered with earth
• Wastes of glass, plastics, and paper should be recycled for further uses.
• Proper and scientific sanitation in every household is necessary to prevent soil pollution.
• Organic pesticides should be used instead of chemical pesticides.
• Proper afforestation can control soil erosion significantly.
• Proper treatment of industrial effluents can lower the amount of pollutants causing soil pollution.
• Radioactive waste material should be treated cautiously to avoid soil pollution.

Green Chemistry

Chemistry is undeniably an important part of our lives since it leads to the formulation and fabrication of medicines, materials, polymers, paints, coatings, electronics etc. Chemists also address fundamental problems like global warming, ozone layer depletion, soil and water pollution, efficient food production via photosynthesis etc.

However, processes on an industrial scale not only produce the desired material, but also large quantities of undesired and toxic chemicals in the form of solids, liquids and gases and have become the biggest challenge that chemists need to face. Hence, there has been a considerable effort to shift to synthetic methods which would minimise environmental pollution. This is where the concept of green chemistry steps in

The U.S. Environmental Protection Agency (USEPA) defines green chemistry as the design of chemical products and processes that reduce the generation of hazardous substances. The use and production of these chemicals and processes may involve reduced waste products, non-toxic components and improved efficiency. Green chemistry is a highly effective approach to pollution prevention because it applies innovative scientific solutions to real-world environmental situations. Green chemistry is also known as sustainable chemistry.

A key difference between environmental chemistry and green chemistry: Environmental chemistry deals with the study of chemical pollutants in the environment whereas green chemistry is concerned with the design of chemicals and processes that minimise toxicity to the environment. This is the key difference between environmental chemistry and green chemistry

1. Applications of green chemistry

The term green chemistry was coined by P. T. Anastas who elucidated the principles of green chemistry in his book ‘Green Chemistry:

1. Prevention: Prevention of waste is better than treatment or cleanup of waste materials.
2. Atom economy: Synthetic methods should be designed such as to maximise the incorporation of all materials into the product.
3. Less hazardous chemical synthesis: Synthetic methods should be designed to minimise toxicity to humans and the environment.
4. Designing safer chemicals: Chemical products must be designed in a manner that their toxicity is reduced, without affecting their desired functions.
5. Safer solvents & Auxiliaries: Use of auxiliary substances (e.g. solvents or separating agents) should be minimised whenever practicable and innocuous when used.
6. Design for energy efficiency: Energy requirements for chemical processes should be minimised and alternative routes for conducting synthesis at ambient temperature and pressure should be probed
7. Use of renewable feedstocks: Green chemistry encourages the use of renewable resources (raw materials or feedstocks) whenever possible.
8. Reduce derivatives: Derivatisation (such as the use of protecting/ de-protecting groups, modification of physical/ chemical processes etc.) leads to the use of additional reagents and the possibility of generating wastes. Such practices should be avoided unless imperative
9. Catalysis: Catalytic reagents are superior to stoichiometric reagents.
10. Design for degradation: Chemical products should be designed so that they decompose into benign products that do not accumulate in the environment.
11. Real-time analysis for pollution prevention: Analytical methodologies should be devised and optimised for real-time, in-process monitoring of chemical processes before the formation of toxic substances.
12. Inherently safer chemistry for accident prevention: Substances and the form of substances must be cautiously chosen to avoid the risk of accidents due to accidental release, explosions, fires etc.

2. Contribution of green chemistry

A few classic chemical processes where green chemistry has proved beneficial are outlined below.

1. Synthesis of Ibuprofen:

Ibuprofen is the active ingredient of several analgesic and anti-inflammatory drugs. The initial synthesis of ibuprofen consisted of a six-step process with a very poor atom economy. However, recent advances has made possible the synthesis of ibuprofen with an atom economy of more than 90%. This synthesis produces less waste and is a three-step process.

2. Use of dense-phase carbon dioxide:

Dense-phase carbon dioxide is used in both homogeneous and heterogeneous catalysis. Its use allows us to replace organic solvents with chemically inert and environmentally non-toxic carbon dioxide. It is used in the food industry as a reusable solvent to ensure minimal nutrient loss and better preservation of the food products. Dense-phase carbon dioxide may also be used to enhance the quality of cement and to reduce the industrial waste of coal plants.

3. Use of liquid carbon dioxide in dry cleaning:

Carbon dioxide is a new environment-friendly alternative for dry’ cleaning. Liquid carbon dioxide effectively removes stains. At the same time, it is less harmful than perchloroethylene, the solvent which is used by 80% dry cleaners.

4. Use of carbon dioxide as a refrigerant:

Chlorofluorocarbons (CFCs) have been extensively used as refrigerants. However, CFCs are now known to be the prince reason for the ‘ozone hole’ in the stratosphere. Carbon dioxide is now used as a refrigerant and has zero ODP (ozone depletion potential) and minimal CWP (global warming potential).

5. Catalytic hydrogenation of diethyl amine:

A greener approach to the catalytic hydrogenation of diethyl amine furnishes a herbicide with the least environmental toxicity.

6. Antifouling agent Sea-Nine:

Sea-Nine (The Dow Chemical Company) is a rapidly biodegradable settlement inhibitor. It is a highly effective antifoulant against bacterial slime, algae, hydrozoids, etc., and is free from heavy metals. Sea-Nine is a good alternative to organotin compounds which cause aquatic toxicity

7. Paper industry and laundry:

Chlorine has long been used for producing good quality paper from wood (by removing all lignin). However, the use of chlorine leads to the formation of chlorinated hydrocarbons which are known to be potential. H₂O₂ is now being used as an alternative in the presence of some activators. The use of H₂O₂ produces lesser environmental concerns.lt is also used in laundry leads lesser use of water.

8. Pyrocool foam:

Pyrocool is used in portable fire extinguishers. It uses a non-toxic foam that cools and extinguishes fire without causing risk to human life. It is also free from volatile organic compounds (VOCs), CFCs and carcinogenic chemicals.

9. Synthesis of antibiotics: Antibiotic drugs like ampicillin and amoxicillin can be synthesised by biochemical methods using environment-friendly enzymes.

10. Sonochemistry: Sonochemistry deals with the study of chemical reactions induced by sound waves.

11. Single-step synthesis of ethanal: A single-step synthesis of ethanal from ethyl alcohol has been studied. This method employs water-soluble ionic catalysts and is environmentally friendly.

12. Fuel cell: A new variety of fuel cells have been fabricated which can be used as batteries in cell phones. Such fuel cells are based on the combustibility of ethanol.

Class 11 Chemistry Environmental Chemistry Long Question And Answers

Question 1. What do you mean by reducing smog and oxidising smog?
Answer:

• Ordinary smog contains sulphur dioxide (SO₂), very fine carbon particles and some other reducing agents.
• As a result of this ordinary smog exhibits reducing property.
• So smog of this type is called reducing smog. Photochemical smog by the presence of oxidising substances such as ozone, NO₂ peroxyacyl nitrate etc. shows oxidising properties.
• As a result of this photochemical smog is sometimes called oxidising smog.

Question 2. What is the Montreal Protocol?
Answer:

• Nowadays, the depletion of the ozone layer in the stratosphere by various greenhouse gases has been a matter of great concern to the scientists of the whole world.
• As a result of this, the decision to prohibit the use of the chief greenhouse gas i.e., chlorofluorocarbon (CFC) was adopted in 1993 in a convention of scientists, arranged in Montreal Canada.
• This is known as the Montreal Protocol. India also signed this agreement

Question 3. What is the Bhopal gas tragedy? Mention the after-effects of the Bhopal gas tragedy.
Answer:

• Bhopal gas tragedy was a gas leak incident in India. This incident is considered as the world’s worst industrial disaster.
• It occurred at the midnight of 2-3 December 1984 at the Union Carbide India Limited (UCIL) pesticide plant in Bhopal, Madhya Pradesh.
• Over 5,00,000 people were exposed to the poisonous methyl isocyanate (MIC) gas.
• Among those people around 3000 people died from the immediate effect of the gas leakage.
• The initial effects of exposure were coughing, vomiting, severe eye irritation and suffocation.
• The people of the affected area still suffering from the after-effects of the tragedy

Question 4. In the stratosphere, ozone is useful but in the troposphere, it is harmful to us— explain.
Answer:

The layer of ozone gas present in the stratosphere which extends from a height of 15 km to 75 km from the sea level of the earth’s surface is known as the ozone layer or ozonosphere.

• The harmful ultraviolet rays (UV rays) coming from the sun is mostly absorbed in the ozone layer because these rays are utilised in the production and dissociation of ozone gas.
• The absence of this ozone layer would allow the ultraviolet rays coming from the sun to reach the earth’s surface entirely.
• This would have heated the earth’s surface and the adjacent air to such an extent that the existence of the living world in land and water would have been jeopardised.
• But, ozone gas present in the troposphere acts as a greenhouse gas.
• Ozone gas contributes nearly 7-8% to the creation of the greenhouse effect.
• Due to greenhouse effects, the surface temperature of the earth will rise and this eventually will melt the polar caps accumulated in polar regions which will cause colossal devastation by tidal waves, cyclones, super cyclones.
• Thus ozone, in the stratosphere is useful but in the troposphere is harmful

Question 5. The extensive depletion of the ozone layer occurs in the months of September to October. Explain this phenomenon.
Answer:

In Antarctica, during the months (March to August) just before the advent of spring season (September-October), the temperature drops below -90°C.

• As a result, the water vapour in the atmosphere condenses to form polar stratospheric clouds.
• Different oxides of nitrogen which are floating in the atmosphere produce nitric acid (HNO₃) in contact with the crystals of ice in the cloud.
• In this condition, chlorine derived from the chlorofluorocarbon (CFC) compounds does not find any opportunity to become inert by reaction with the oxides of nitrogen because chlorine is not capable of reacting with the nitric acid.
• As a consequence of this phenomenon, during the few months from March to August (when the sky in Antarctica remains covered with darkness), chlorine keeps on accumulating in the stratosphere.
• Then, with the arrival of spring, the chlorine present in the atmosphere becomes very reactive in the presence of sunlight and triggers the process of breaking of ozone (O₃) molecules in the ozone layer.
• Thus, extensive depletion of the ozone layer takes place in September to October

Question 6. Name the greenhouse gases and mention their sources due to human activities.
Answer:

Question 7. What is an atomic power plant? What Is Chernobyl Disaster? What is the cause of this accident?
Answer:

The power plant produces electricity by the nuclear fission reaction of radioactive elements such as uranium. plutonium etc. is called atomic power plant

Chornobyl is a city in Ukraine in the former Soviet Union. On the 26th of April, 1986, the accident that occurred with horrifying consequences and destroyed the environment has remained alive in our memory as the Chornobyl disaster.

As a result of this tragic accident, the radioactive emission spread over an area of about 3000 sq km and nearly ten crores of people had to be rehabilitated. Uranium was used as fuel in the plant for the generation of electricity. On the day of the accident, due to the lack of proper safety measures, uranium fuel in the atomic reactor, being exceedingly heated, caused the explosion

Question 8. Carbon monoxide gas is more dangerous than carbon dioxide gas. Why?
Answer: 

The colourless, odourless carbon monoxide gas is severely harmful for human beings and animals. It has a greater affinity towards haemoglobin than that of oxygen. So, it readily displaces oxygen from oxyhaemoglobin (HbO₂) to form the more stable compound carboxyhaemoglobin (HbCO) to give a stable compound, carboxyhaemoglobin

HbO₂ + CO ⇌  HbCO + O₂

In blood, when the concentration of carboxy haemoglobin reaches 3-4%, the oxygen-carrying capacity of the blood is greatly reduced. In other words, the body becomes oxygen-starved. results in headache, nervousness, cardiovascular disorder, weak eye-sight etc., On the other hand, CO₂ does not combine with haemoglobin and hence is less harmful as a pollutant. CO₂. is mainly responsible for the greenhouse effect and global warming

Question 9. What are the harmful effects of photochemical smog and how can they be controlled?
Answer:

Photochemical smog can be controlled in the given ways: 

By using efficient catalytic converters in the automobiles which will check the release of both NO₂  and certain hydrocarbons known as primary precursors.

• This will automatically check the formation of secondary precursors. Such as Ozone and PAN.
• By spraying certain compounds into the atmosphere which will control hydrocarbons, NO₂, and PAN.
• Certain plants like pinus, Pyrus, Vitis Quercus etc., are capable of causing the metabolism of the oxides of nitrogen. Hence their plantation could be helpful.

Question 10. What are herbicides? Explain giving
Answer:

Herbicides:

• These are the chemicals employed to control weeds. The common herbicides are sodium chlorate (NaClO₃) and sodium arsenite (Na₃AsO₃).
• These herbicides are no longer preferred because they are toxic towards mammals.
• At present organic herbicides like triazines are used as weed controllers and have no adverse effect on human beings

Question 11. A large number of fish are suddenly found floating dead on a lake. There is no evidence of toxic dumping but you find an abundance of phytoplankton. Suggest a reason for the fish kill
Answer:

• The presence of excess phosphate and nitrate compounds increases the growth of phytoplankton (organic pollutants such as leaves, grass, trash etc.).
• A large population of bacteria decomposes this organic pollutant.
• During this process, they consume the dissolved oxygen of water which is of course very much essential for the life of sea animals, particularly fish.
• When the level of dissolved oxygen falls below 6 ppm, the fish cannot survive.
• Hence a large number of fish are found floating dead on the lake

Question 12. How can domestic waste be used as manure?
Answer:

• Domestic wastes consist of two types of materials, biodegradable such as leaves, rotten food, vegetable refuse etc., and non-biodegradable portion which consists of plastic, glass, metal scrap etc.
• The biodegradable waste should be deposited in the landfills.
• Then this waste gets converted into time

Question 13.  For your agricultural field or garden, you have developed a compost-producing pit.  Discuss the process in the light of bad odour, flies and recycling
Answer:

• The compost-producing pit should be developed at a suitable place to protect ourselves from bad odour and flies.
• It should be covered properly to prevent the entry of flies and the emission of foul odour.
• The waste materials like plastics, glass, newspapers etc must be handed over to the vendors.
• These are finally sent to the recycling industry without creating a pollution problem

Class 11 Chemistry Environmental Chemistry Short Question And Answers

Question 1. How are NO and NO₂ produced in the atmosphere?!
Answer:

Due to lightning discharge in the upper atmosphere, nitrogen and oxygen combine to produce nitric oxide. This nitric oxide (NO) reacts with aerial oxygen to give nitrogen dioxide.  (NO₂) Because of the bacterial decomposition of ammonium salts in the soil, NO is produced. Besides these, combustion of fossil fuels also serves as a potential source of NO and NO₂

Question 2. In the presence of carbon monoxide, haemoglobin loses its oxygen-carrying capacity causing oxygen starvation of body cells—explain
Answer:

Carbon monoxide has a strong affinity for haemoglobin This gas combines with haemoglobin to form highly stable carboxyhaemoglobin

Consequently, the availability of oxygen in the body cells decreases, because haemoglobin fails to carry the oxygen necessary for the life process to continue. So carbon monoxide present in excess may sometimes cause death

Question 3. Many spray bottles from which a perfume is sprayed contain a very harmful substance. By what name is it commonly known? Why is it harmful?
Answer:

The harmful constituent is chlorofluorocarbons (CFCs) or Freons. When they diffuse into the upper atmosphere, they absorb ultraviolet radiation which ruptures carbon-chlorine bonds to give chlorine atoms. The chlorine atoms thus produced cause destruction of the ozone layer which shields the earth from the harmful effects of ultraviolet radiation of the sun. This is the reason for which CFCs are very harmful.

Question 4. What is hypothermia?
Answer:

Mineral oil and by-products of oil get dispersed in water for various reasons, thereby contaminating it. When a bird comes in contact with this polluted water, the oil floating on the surface of the water penetrates the feathers and wings of the bird. This in turn annihilates the possibility of the bird’s flight. In addition, the temperature of the bird’s body drops considerably resulting in its death. This phenomenon is called hypothermia

Question 5. What were the components of London Smog? What was its nature?
Answer:

Finely divided particles, water vapour, SOx and quantity of NO It was reducing in nature because the non-metallic oxide SO₂ was mainly present in it as a reducing agent

Question 6. It was reducing in nature because the non-metallic oxide, SO₂ was mainly present in it as a reducing agent
Answer:

O₃, NO₂ Peroxyacyl nitrate (PAN), aldehyde, ketone, hydrocarbons and CO. It was oxidising in character, because O₃, NO₂ peroxyacyl nitrate etc., were present in it as oxidising agents. peroxyacetyl nitrate etc., were present in it as oxidising agents

Question 7. What is the temperature range of the atmosphere? What do you mean by inversion temperature in different regions of the atmosphere?
Answer:

-56°C to 1200°C . When we traverse from one region of the atmosphere to the next adjoining region, the trend of temperature changes successively from higher to lower or vice versa. This is called inversion temperature

Question 8. What is marine pollution? What is siltation?
Answer:

The pollution of seawater due to the discharge of wastes from different sources into it thereby making it harmful for human health and aquatic life is called marine pollution. Mixing of soil and rock particles into water is called siltation. The soil particles produce turbidity in water thereby hindering free movement of aquatic organisms.

Question 9. What is the Polar Vortex? What is its effect?
Answer:

A tight whirlpool of wind formed in the stratosphere surrounding Antarctica is called the Polar Vortex. It is so rigid that it cuts off Antarctica from the surrounding ozone-rich air of the non-polar regions. Thus, as long as the polar vortex surrounds Antarctica, the ozone hole remains unfilled

Question 10. What is an ozone umbrella? Why is it called so?
Answer:

Ozone layer present in the stratosphere is called the ozone umbrella. Like an umbrella, the ozone layer prevents harmful. UV radiation from reaching the earth. Thus, the ozone layer is also called the ozone umbrella.

Question 11. In hospitals, patients with CO poisoning are kept in high-pressure chambers containing oxygen at 2 to 2.5 atm pressure—why?
Answer:

Under high pressure of oxygen, CO of carboxyhaemoglobin (HbCO) is replaced by O₂ and thus transport of O₂ to different parts of the body starts.

HbCO + O₂ ⇌  HbO₂+CO

Question 12. What is the role of CO₂ in creating the greenhouse effect?
Answer:

A part of the infrared rays of longer wavelength, emitted by the earth’s surface on being heated by the sun rays is absorbed by CO₂ gas molecules and the return to the earth’s surface along with the surrounding atmosphere gets heated

Question 13. What is Polar Stratospheric Clouds (PSCs)?
Answer:

In Antarctica, the climatic conditions are quite different. In winter, there is no sunlight and the temperature is very low. The low temperature causes the formation of special types of clouds over Antarctica which are called Polar Stratospheric Clouds (PSCs).

Question 14. In which regions atmosphere, temperature increases with altitude and in which regions it decreases?
Answer:

• In the stratosphere and thermosphere temperature increases with altitude, while in the troposphere and mesosphere, temperature decreases with altitude
• In which season the depletion of the ozone layer in Antarctica takes place and when is it replenished
• During spring (in September and October) ozone layer depletion occurs in Antarctica, while after spring

The gaseous and particulate pollutants are:

1. Gaseous air pollutants: These are mainly oxides of sulphur (SO₂, SO₃), oxides of nitrogen (NO, NO₂) and oxides of carbon (CO, CO₂), H₂S, hydrocarbons, ozone and other oxidants.
2. Particulate pollutants: Particles in the form of smog, dust, mist, smoke etc., belong to this category

Class 11 Chemistry Environmental Chemistry Multiple Choice Question

Question 1. The ozone layer forms naturally by—

1. The interaction of CFC with oxygen
2. The interaction of UV radiation with oxygen
3. The interaction of IR radiation with oxygen
4. The interaction of oxygen and water vapour

Answer: 2. The interaction of UV radiation with oxygen

The ozone layer forms naturally by the interaction of UV radiation with oxygen

Question 2. Among the following, the one which is not a “greenhouse gas” is

1. N₂O
2. CO
3. CH ₄
4. O

Answer: 4. O

O₂ is not a gas responsible for the rise in temperature of the earth. So, O₂ is not a ‘greenhouse gas

Question 3. Metal ion responsible for the Minamata disease is

1. CO
2. Hg²⁺
3. Cu
4. Zn²⁺

Answer: 2. Hg²⁺

Hg²⁺ ion is responsible for the Minamata disease.

Question 4. What is DDT among the following

1. A fertilizer
2. Biodegradable pollutant
3. Non-biodegradable pollutant
4. Greenhouse gas

Answer: 3.  Non-biodegradable pollutant

DDT is a non-biodegradable pollutant

Question 5. The gas leaked from a storage tank of the Union Carbide plant in Bhopal gas tragedy was O₂

1. Phosgene
2. Methylisocyanate
3. Methylamine
4. Ammonia

Answer: 2. Methylisocyanate

Methylisocyanate gas was leaked from a storage tank of the Union Carbide plant in the Bhopal gas tragedy.

Question 6. The concentration of fluoride, lead, nitrate and iron in a water sample from an underground lake was found to be 1000 ppb, 40 ppb, 100 ppm and 0.2 ppm respectively. The water is unsuitable for drinking due to high concentration

1. Fluoride
2. Lead
3. Nitrate
4. Iron

Answer: 3. Nitrate

In the sample of water, the concentration of fluoride, lead and iron are in permissible limit but the concentration of nitrate ion is much higher than its permissible limit. Thus the water is not suitable for drinking.

Question 7. A water sample has ppm level concentration of the following anions, F^– = 10, SO₄^2-= 10, NO₃^– = 50. The anion/ anions that make/makes the water sample unsuitable for drinking is/are—

1. Only F^–
2. Only SO₄^2-
3. Only NO₃^–
4. Both SO₄^2- And NO₃^–

Answer: 1. Only F^–

In drinking water, if the concentration of SO₄^2- is more than 500 ppm, it shows a laxative effect and it is not suitable for drinking. If the concentration of SO₄^2-  is less than 500 ppm, it is consumable.

In drinking water, if the concentration of NO₃  ion is more than 50 ppm it causes methemoglobinemia disease. This is not suitable for drinking. If the concentration of F“ ion in drinking water is more than 1 ppm it damages teeth and bones. Thus it is not suitable for drinking

Question 8. The recommended concentration of fluoride ion in drinking water is upto 1 ppm as fluoride ion is required to make teeth enamel harder

1. [3Ca₃(PO₄)₂ Ca(OH)₂]
2. [3Ca₃(PO₄)₂ .CaF₂]
3. [3{Ca(OH)₂} . CaF₂]
4. [3(CaF₂) . Ca(OH)₂]

Answer: 1. [3Ca₃(PO₄)₂ Ca(OH)₂]

Generally, tooth enamel is hydroxyapatite [3Ca₃(PO₄)₂ Ca(OH)₂].  Fluoride ion (F^–) reacts with hydroxyapatite to form a more rigid solid compound fluorapatite.

Question 9. Which one of the following statements is not true 

1. Oxides of sulphur, nitrogen and carbon are the most widespread air pollutants
2. PH of drinking water should be between 5.5-9.5
3. A concentration of DO below 6 ppm is good for the growth of fish
4. Clean water would have a BOD value of less than 5 ppm

Answer: 3.  A concentration of DO below 6 ppm is good for the growth of fish

Fish growth is facilitated if the DO value is less than 6 ppm. A decrease in the Do value means an increase in water pollution

Question 10. Which one of the following statements regarding photochemical smog is not correct

1. Photochemical smog is formed through a photochemical reaction involving solar energy
2. Photochemical smog does not irritate the eyes and throat
3. Carbon monoxide does not play any role in photochemical smog formation
4. Photochemical smog is an oxidising agent in character

Answer: 2. Photochemical smog does not irritate eyes and throat

Question 11. Which one of the following is not a common component of photochemical smog

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

Answer: 4. Chlorofluorocarbons

Question 12. Which of the following is a sink for CO

1. Microorganisms present in the soil
2. Oceans
3. Plants
4. Haemoglobin

Answer: 1.  Microorganisms present in the soil

Question 13. Which oxide of nitrogen is not a common pollutant introduced into the atmosphere both due to natural and human activity

1. NO
2. N₂O₅
3. N₂O
4. NO₂

Answer: 2.  N₂O₅

Question 14. Living in the atmosphere of CO is dangerous because it

1. Combines with O₂ present inside to form CO₂
2. Reduces organic matter of tissues
3. Combines with haemoglobin and makes it incapable of absorbing oxygen
4. Dries up the blood

Answer: 3. Combines with haemoglobin and makes it incapable of absorbing oxygen

Question 15. Which of the following is not a greenhouse gas

1. Hydrogen
2. Carbon dioxide
3. Methane
4. Nitrous oxide or NO₂

Answer: 1.  Hydrogen

Carbon dioxide, methane, water vapour, nitrous oxide, CFCs and ozone are greenhouse gases

Question 16. Which of the following has the highest concentration of PAN

1. Smoke
2. Ozone
3. Photochemical smog
4. Reducing smog

Answer: 3.  Photochemical smog

The main component of photochemical smog is peroxyacetyl nitrate, (PAN). The other components are ozone, nitric oxide, acrolein and formaldehyde

Question 17. Which of the following is not a greenhouse gas?

1. Carbon dioxide
2. Water vapours
3. Methane
4. Oxygen

Answer: 4.  Oxygen

Carbon dioxide, water vapours and methane are greenhouse gases

Question 18. Which air pollutants do not evolve from motor vehicles

1. Formaldehyde
2. Carbon dioxide
3. Fly ash
4. Sulphur dioxide

Answer: 3. fly ash

Question 19. The top layer of the atmosphere is

1. Stratosphere
2. Troposphere
3. Exosphere
4. Ionosphere

Answer: 3. Exosphere

Question 20. Which of the following is not an air pollutant

1. NO
2. CO
3. O₃
4. C_xH_y

Answer: 2. CO

Question 21. Which of the following has the highest affinity towards haemoglobin 

1. CO
2. NO
3. O₂
4. CO₂

Answer: 1. CO

Question 22. Which gas is not present in the ozone layer

1. O₂
2. O₃
3. N₂
4. CO

Answer: 4. CO

Question 23. Fluoride pollution mainly affects

1. Teeth
2. Brain
3. Kidney
4. Heart

Answer: 1.  Teeth

Question 24. Which metal is mainly responsible for the decline of the Roman Empire

1. Copper
2. Lead
3. Arsenic
4. Zinc

Answer: 2.  Lead

Question 25. Which of the given pollutants does not affect the lungs

1. CO
2. SO₂
3. CO
4. NO

Answer: 3. CO

Question 26. Which of the following statements is not true

1. Ozone gas has no role in the greenhouse effect
2. Ozone gas oxidises sulphur dioxide of the atmosphere to sulphur trioxide
3. Gradual thinning of the ozone layer leads to the formation of an ozone hole
4. Oxygen molecule in the stratosphere forms ozone molecules in the presence of ultraviolet radiation

Answer: 1.  Ozone gas has no role in the greenhouse effect

Question 27. Although nitrogen and oxygen are the major constituents of air, they do not react with each other to produce oxides of nitrogen because

1. As the reaction is exothermic, a high temperature is required
2. A catalyst is required for the initiation of the reaction
3. Oxides of nitrogen are unstable
4. Nitrogen and oxygen do not take part in the reaction

Answer: 1. As the reaction is exothermic, a high temperature is required

Question 28. Which of the following is a secondary air pollutant

1. CO
2. CH
3. PAN
4. NO

Answer: 3. PAN

Question 29. Which of the given fuels used in motor vehicles is not environment friendly

1. Dye
2. Petrol
3. LPG
4. CNG

Answer: 4. LPG

Question 30. A major source of methane in India

1. Fruit garden
2. Sugarcane field
3. Paddy fields
4. Wheat fields

Answer: 3.  Paddy fields

Question 31. Cause of stenosis diseases

1. Fly ash
2. Cement particles
3. Cotton fibre
4. Lead particles

Answer: 3.  Cotton fibre

Question 32. The poisonous substance used in the paper is

1. Cadmium
2. Lead
3. Manganese
4. Mercury

Answer: 2.  Lead

Question 33. Which reaction is carried out in the catalytic converter of motor vehicles to eliminate NO_x from smoke

1. Oxidation
2. Reduction
3. Both oxidation-reduction
4. None

Answer: 2. Reduction

Question 34. Which of the following causes depletion in the ozone layer directly

1. SO₂
2. CFCs
3. H₂O
4. NO

Answer: 1. SO₂

Question 35. The incomplete combustion of gasoline produces

1. CO₂
2. CO
3. SO₂
4. NO₂

Answer: 2. CO

Question 36. Value of pH in drinking water—

1. Between 5.3 to 6.5
2. <5.5
3. Between 5.5 to 9.5
4. 9.5

Answer: 3. Between 5.5 to 9.5

Question 37. The radiation has a specific biological effect but is unable to cause Ionisation Is

1. UV-radiation
2. β -ray
3. X-ray
4. y-ray

Answer: 1.UV-radiatlon

Question 38. Which of the following compounds increases the BOD value of the water supply

1. CO₂
2. O
3. H₂O
4. CHOH

Answer: 4.  CHOH

Question 39. Which is most harmful for a human being

1. UV- A
2. UV – BOD
3. UV – CO₂
4. UV- DDT

Answer: 2. UV – BOD

Question 40. DDT and BHC are

1. Antibiotic
2. Chemical fertilizer
3. Non-biodegradable pollutant
4. Biodegradable compound

Answer: 3.  Non-biodegradable pollutant

Question 41. Which component of motor vehicle smoke causes nerve and mental diseases

1. Hg
2. SO₂
3. Pb
4. NO

Answer: 3. Pb

Question 42. Which mercury compound is the most toxic in nature

1. CH₃Hg⁺
2. HgCl₂
3. Hg₂Cl₂
4. Hg metal

Answer: 1. CH₃Hg⁺

Question 43. Example of herbicide

1. DDT
2. Triazines
3. Methylmercury
4. PCBS

Answer: 2.  Triazines

Question 44. Nitrogen oxide is not a major air pollutant

1. NO₂
2. N₂O
3. NO
4. N₂O₅

Answer: 4. N₂O₅

Question 45. pH of natural rainwater

1. 6.5
2. 3.5
3. 4.6
4. 5.6

Answer: 4. 4.6

Question 46. Which water pollutant metal causes sterility disease

1. Cu
2. Hg
3. Cd
4. Mn

Answer: 4.  Mn

Question 47. The minimum permissible level of sound pollution is

1. 75 dB
2. 65 dB
3. 55 dB
4. 50 dB

Answer: 1. 75 dB

Question 48. In acid rain which of the following are present

1. H₂CO₃
2. HNO₃
3. CH₃COOH
4. H₂SO₄

Answer: 1, 2, and 4

Question 49. If fertilizer containing phosphate is dissolved in water

1. The amount of dissolved oxygen decreases
2. Calcium phosphate precipitates
3. Growth of fish increases
4. The growth of aquatic plants increases

Answer: 1 and 4

Question 50. Result of global warming

1. The temperature of the earth’s surface will increase
2. Glaciers of the Himalayan region will melt
3. Demand of biochemical oxygen will increase
4. Eutrophication

Answer: 1 and 2

Question 51. Which are responsible for photochemical smog

1. Oxides of nitrogen
2. Hydrocarbons
3. Carbon monoxide
4. Nobel gases

Answer: 1, 2, and 3

Question 52. Which gases absorb IR radiation

1. O₂
2. NO₂
3. CO
4. CFC

Answer: 3 and 4

Question 53.  Depletion in the ozone layer is caused by

1.  So₂
2. Halons
3. NO
4. C_xH_y

Answer: 2 and 3

Question 54. Which of the following states are responsible for environmental pollution

1. pH value in rainwater is 5.6
2. Eutrophication
3. The BOD value in the water sample is 15 ppm
4. The amount of CO₂ in the atmosphere is 0.03%

Answer: 2, and 3

Question 55. Which processes occur in the troposphere

1. Photosynthesis
2. Combustion
3. Greenhouse effect
4. Acid rain

Answer: 1, 2, 3 and 4

Question 56. Which statements are true

1. Mainly the effects of HNO₃ are more in acid rain
2. NO is more toxic than NO₂
3. Ozone gas is responsible for the greenhouse effect
4. IR radiation cannot pass through CO₂ gas but gets absorbed by it

Answer: 3 and 4

Question 57. Which radical causes depletion in the Ozone layer

1. CH₃
2. F
3. Cl
4. Br

Answer: 3 and 4

Question 58. Which greenhouse gases are produced in the agriculture field

1. CH₄
2. NH
3. Nobel
4. SO

Answer: 1 and 4

Question 59. Which are the following statements are incorrect

1. SO₂ does not affect the larynx
2. SO₂ is a more harmful pollutant than SO₃
3. In the case of living cell NO₂ is more toxic than NO
4. There is no role of NO_x in photochemical smog

Answer: 1, 2 and 4

Question 60. Diseases caused by the harmful effects of SO₂ 

1. Digestion problem
2. Breathing problem
3. Bronchitis
4. Asthma

Answer: 2, 3 and 4

Question 61. Which of the following processes are responsible for the formation of CO₂ in the atmosphere

1. Respiration
2. Combustion of fossil fuel
3. Decay of animals
4. Production of cement in factories

Answer: 2 and 4

Question 62. Which of the following react to produce PAN

1. NO
2. O₂
3. Hydrocarbon
4. CO

Answer: 1, 2 and 3

Question 63. Which constituents of phytochemicals responsible for eye irritation

1. Ozone
2. PAN
3. Hydrocarbon
4. O₂

Answer: 1 and 2

Question 64. The main constituents of London smog are

1. Oxides of sulphur
2. O₂
3. O₃
4. Oxides of nitrogen

Answer: 1 and 4

Question 65. Which of the following is responsible for the depletion of the ozone layer in the stratosphere

1. So
2. CFCl
3. CF
4. CF Br

Answer: 2 and 4

Question 66. Which of the following are primary pollutants

1. PAN
2. SO
3. NOz
4. Me₂Hg

Answer: 2 and 3

Question 67. Contribution of CO₂ and CH₄ in greenhouse effects

1. The contribution of CO₂ is 50%
2. The contribution of CH₄ is 16%
3. The contribution of CO₂ is 19%
4. The contribution of CH₄ is 19%

Answer: 1 and 4

Question 68. In which region there is a greater possibility of formation of photochemical smog

1. Region where a large number of automobiles are used
2. Region where sulphur-containing coal is used
3. Marshy land region
4. Orest region

Answer:  1. Region where large number of automobiles are used

Question 69.  Acid rain is a dilute aqueous solution of which of the following pairs of acids

1. H₂SO₄ and HCl
2. H₂CO₃ and HCl
3. H₂SO₄ and HNO₃
4. H₂CO₃ and HCl

Answer: 3 . H₂SO₄ and HNO

Question 70. Which of the following metallic air pollutants is present in the gas emitted by motor vehicles

1. Iron
2. Lead
3. Copper
4. Mercury

Answer: 2.  Lead

Question 71.  Which of the following is not a Greenhouse gas

1. CFCs
2. Ammonia
3. Carbon dioxide
4. Methane

Answer: 2. Ammonia

Question 72. Which compound is responsible for hole formation in the stratosphere of the ozone layer

1. C₆F₆
2. C₆H₄Cl₂
3. CCl₂F₂
4. C₆H₆

Answer: 3. CCl₂F₂

Question 73. Which of the following gases emitted by motor vehicles is responsible for the formation of photochemical smog

1. SO₂
2. CO
3. NO
4. CO₂

Answer: 3. NO

Class 11 Chemistry Environmental Chemistry Very Short Question And Answers

Question 1. What are the chief air pollutants?
Answer: 

SO₂, SO₃, CO, CO₂, NO₂, NO, O₃, hydrocarbons, fine particles of solid or liquid suspended in air.

Question 2. What are the main pollutants emitted from thermal power plants?
Answer: CO, CO₂, NO, NO₂, fly ash etc.

Question 3. Name the sink of CO.
Answer: A special type of bacteria present in the soil, which converts CO into C0

Question 4.  Name two sinks of CO₂
Answer: Sea water (which dissolves CO₂) and plants (which use CO₂ for photosynthesis).

Question 5. Which aromatic compound is present in the air as particulate?
Answer: Polycyclic aromatic hydrocarbons (PAH) like benzopyrene

Question 6. What is PCB?
Answer:  PCB is polychlorinated biphenyl. It is highly toxic

Question 7. What is the role of particulates in the formation of clouds?
Answer:  Particulates act as nuclei in the formation of clouds.

Question 8.  What 31-6 are the main compounds responsible for causing damage to the ozone layer?
Answer:  Freons and nitric Oxide (NO) are the main compounds fo cause damage to the ozone layer

Question 9. What is the role of the builder in synthetic detergents?
Answer: It removes hardness-producing ions {viz., Ca²⁺, Mg²⁺) from water

Question 10. Which of the atmospheric layers contains the maximum ozone gas?
Answer: Stratosphere

Question 11. Mention the range of temperature of the atmosphere.
Answer: From -92°C to +1200°C

Question 12. What is the main source of carbon monoxide in the atmosphere?
Answer: Coal, Petrol and incomplete combustion of other fossil fuels,

Question 13. Which one is more harmful to the human body— CO or C°2?
Answer: CO

Question 14. What are the main pollutants produced by forest fires?
Answer: CO , CO₂ , NO , NO₂

Question 15. What are the major pollutants emitted by thermal power plants?
Answer: CO, CO₂, NO, NO₂,flash

Question 16. What are the ads present in acid rain?
Answer:  H₂SO₄, HNO₃ and HC

Question 17. What is the size of the particulates?
Answer: From 0.0002 μ to 500p

Question 18. What Is the main chemical responsible for the Bhopal gas tragedy?
Answer: Methyl isocyanate (MIC)

Question 19. By which disease do the workers of asbestos factories suffer?
Answer: Asbestosis

Question 20. Give one example of a fire extinguisher made by Pyrocool technology.
Answer: Pyrocoolfoam

Question 21. Which acid contributes most to the formation of acid rain?
Answer: Sulphuric acid (H₂SO₄)

Question 22. Mention the H limit of acid rain
Answer: From 5.6 to 3.5

Question 23. Give thefullform of’PAN’.
Answer: Peroxyacyl nitrate

Question 24. Which unit is used to measure the columnar density of O₃ gas in Earth’s atmosphere?
Answer: Dobson (Du) unit.

Question 25. Which gas has the maximum contribution to the greenhouse effect?
Answer: Carbon dioxide (CO₂)

Question 26. Among the air pollutants gas is responsible for the damage caused to the TajMahal
Answer: Sulphur dioxide (SO₂)

Question 27. Mention two diseases originating from water pollution
Answer: Cholera, typhoid

Question 28. What is the cause? Bhopal gas tragedy
Answer: Methyl isocyanate gas

Question 29. Name a nitrogen-fixing bacteria
Answer: Rhizobium

Question 30. Name the main air pollutant that is present in automobile exhausts.
Answer: Carbon monoxide (CO)

Class 11 Chemistry Environmental Chemistry Fill In The Blanks

Question 1. The total mass of gaseous substances in the atmosphere is nearly ____________________
Answer: 5.5 × 10¹⁵ ton

Question 2. The amount of CO₂ in the atmosphere is approximately is more harmful ___________________
Answer: 2. 0.031%

Question 3. CO₂ when mixed with blood, forms ___________________
Answer: Carboxyhaemoglobin,

Question 4. The word, ‘CFC’ means___________________
Answer: Chlorofluorocarbon

Question 5. The word, ‘PAN’ stands for___________________
Answer: Peroxyacyl nitrate

Question 6. The formation of ozone hole increases the tendency of human beings to be attacked by ___________________
Answer: Cancer

Question 7. One remarkable phenomenon happened in the troposphere is___________________
Answer: Green House effect

Question 8. Between NO₂ and NO__________________
Answer: NO₂

Question 9. The word, ‘PAH’ denotes __________________
Answer: Polyaromatic hydrocarbon

Question 10. The lung disease caused by silica is __________________
Answer: Silicosis

Question 11. Among the following gases _____________ is a greenhouse gas (NO₂, N₂O, SO₂ , NO)
Answer: NO

Question 12. The causes of Minamata is____________ containing effluent.
Answer: Mercury

Class 11 Chemistry Environmental Chemistry Warm-Up Question And Answers

Question 1. What Is fly ash?
Answer:

Fly ash is emitted from thermal power plants due to the combustion of coal. It consists of fine particles of SiO₂

Al₂O₃, CaO, Fe₂O₃, NO₂, SO₂, P₂O₃

Question 2. What are the sinks for CO₂ and CO gases?
Answer:

Sea water (CO₂ is soluble here) and some special bacteria (which absorb CO and convert it into CO₂

Question 3. Mention three hydrocarbons which function as air pollutants.
Answer:

1,3-butadiene, 1,2-benzopyrene, 1,2-benzanthracene

Question 4. Name three primary and three secondary air pollutants.
Answer:

1. Primary air pollutants: CO, SO₂, NO₂;
2. Secondary air pollutants: O₃, PAN, formaldehyde

Question 5. Name some hydrocarbons that are present in the atmosphere as organic particulates.
Answer:

Methane, benzene, benzopyrene

Question 6. Name the compounds responsible for ozone hole formation.
Answer:

Chlorofluorocarbons, halons etc

Question 7. Why the temperature of the stratosphere increase with the increase in height?
Answer:

The ozone layer in the stratosphere absorbs the harmful ultraviolet radiation coming from the sun and converts it into heat. Thus the temperature of this layer increases.

Question 8. What are halons? State their uses
Answer:

Halons arc halocarbons. They used as fire extinguishers

Question 9. Why is the tropospheric ozone harmful?
Answer:

Ozone gas present In the troposphere acts as a greenhouse gas.

Question 10. Mention the season and time of the day when London smog is generally observed.
Answer:

During winter, particularly after evening or early in the morning London smog is generally observed

Question 11. Mention the season and time of the day when Los Angeles smog is generally observed
Answer:

During the mid-days of the summer season when the sun shines brightly this kind of smog is observed.

Question 12. Which region is most susceptible to the formation of photochemical smog?
Answer:

Photochemical smog is mostly observed in big cities, where there is considerable vehicular traffic on the roads throughout the whole day and night

Question 13. Why is photochemical smog called Los Angeles smog?
Answer:

This type of smog was first discovered in the city of Los Angeles in America in the year 1950. So it is called Los Angeles smog.

Question 14. ‘There is “a ‘ tendency of environmental degradation of Tajmahal Explain
Answer:

SO₂ released from the industries situated around Tajmahal reacts photochemically with atmospheric O₂ and water vapour to form H₂SO₄. The H₂SO₄ hence produced reacts with white marble and damages it

Question 15. Give two examples of chlorinated organic pesticides.
Answer:

p, p’ -dichlorodiphenyltrichloroethane (DDT) and benzene hexachloride (BHC)

Question 16. What is loam soil?
Answer:

The soil containing almost equal amounts of sand, slit and clay along with humus, 34% of air and 64% of water is called loam soil

Question 17. Give two examples of each insecticide and herbicide
Answer:

Insecticide: DDT, BHC

Herbicide: 2,4-dichloro phenoxy acetic acid, dioxin

Question 18.   Write one effect of the depletion of the ozone layer and one measure for the prevention of ozone layer depletion.
Answer:

We have to reduce the use of compounds made by CFCs and halons

Question 19. Explain tropospheric pollution in 100 words.
Answer:

Tropospheric pollution occurs due to the presence of undesirable poisonous gases and solid particles in the air.

Question 20. What is anoxia or asphyxiation?
Answer:

Acute oxygen starvation in the body due to poisoning by carbon monoxide is called anoxia or asphyxiation

Question 21. What is humification
Answer:

The process of decomposition of organic matter (roots, leaves etc.) in the soil by microorganisms to produce humus is called humification.

Question 22. Why does the population of fish get hindered by clouds? thermally polluted water
Answer:

Thermal pollution increases the temperature which in turn decreases the DO level of the water. Thus, it affects the fishes badly and their growth gets retarded

Question 23.  Name four natural sources of air pollution.
Answer:

Volcanic eruptions, forest fires, lightning, decomposition of dead plant and animal bodies in marshyland.