12th Class Chemistry Chapter 16 Environmental Chemistry Short Question Answers

That branch of chemistry which deals with the chemical and other pollutants in the environment is called environmental chemistry. In this branch of chemistry we study sources reactions transportation of chemicals and transportation of toxic substance.

Environment is consisted of following four components: i) Atmosphere. ii) Hydrosphere iii) Lithosphere iv) Biosphere/Ecosphere

Atmosphere is composed of 78% N₂, 21% O₂, 0.9% Ar, 0.03% CO₂ and some trace amounts of H₂ O₃. CH₃ CO and noble gases. The concentration of water vapours changes with time.

Atmosphere absorbs most of the cosmic rays and U.V rays but the radiations whose wavelengths lie between 300-2500 nm are not absorbed and they include near U.V visible near I.R.

i) Oxygen is required for breathing.
ii) CO₂ for photosynthesis.
iii) N₂ for fixation of bacteria.
iv) Water vapours for various forms of life moreover the atmosphere maintains the heat balance on the earth due to water vapours.

Hydrosphere contains water and the major water resources are oceans rivers streams lakes polar ice caps glaciers and ground water reservoirs. 97% of the water is in the oceans and 2% in polar ice caps and glyciers 1% of the total is fresh water.

Lithosphere is the component of environment which is consisted of rigid rocky crust of earth 99.5% of the lithosphere has the composition as 46.6% oxygen 27.72% silicon 8.13% aluminium 5% Fe  and rest are some other metals.

The component of the environment which indudes the region of Earth which is capable of supporting life is called biosphere. It is consisted of lower atmosphere oceans river lakes soils and solid sediments.

Any substance in the environment which has adverse effects on human health quality of life and natural functioning of ecosystem is called environmental pollutants. The rapid growth of population urbanization industrialization and transportation are the main factors which are responsible for environmental pollution.

The primary pollutants are:
i) Waste products which escape from chimneys of industrial units.
ii) Exhausts of automobile.
iii) The gases like SO₂ SO₃ oxides of nitrogen CO hydrocarbons and radioactive materials are the primary pollutants.

The following substances are the secondary air pollutants. These are H₂SO₄ N₂O H₂CO₃ HF P.A.N ozone aldehydes and ketones.

Volcanic eruption natural gas emission oxidation of CH₄ forest fires of wood fossil fuel buming of agricultural products are the major sources of CO. 75%  of total CO is from motor vehicles railways and aircrafts.

i) Incomplete combustion of any fuel.
ii) Reaction between CO₂ and carbon.
iii) Dissociation of CO₂ at high temperature.

It combines with the haemoglobin to give carboxylhaemoglobin. It is scarlet red in color and it is much more stable. It decreases the oxygen carrying capability.

It Creates the following Problems: i) Headache. ii) Fatigue. iii) Unconsciousness. iv) Eventual death.

No and NO₂ are air pollutants. They are mostly produced from:
i) Combustion of coal.                 ii) Combustion of oil.
iii) Combustion of natural gas.

i) Volcanoes(76%)             ii) Oxidation of sulphur.
iii) Combustion of coal             iv) Burning of crude oil.
v) Burning of fossil fuel.           Vi) Petroleum industries.

SO₂ and SO₃ give various reactions in the atmosphere and they form sulphate aereosoles. They can penetrate in the human body through lungs.

Methane is a gas. It is mixed up in air from the following sources: i) Emitted by different trees and plants in the atmosphere. ii) Paddy fields produce large amount of methane in the atmosphere. iii) Anaerobic decomposition of organic matter. iv) Domestic animal also produce methane.

The dissolution of CO₂ SO₂ and NO₂ in rain water create acids. These acids reach the surface of the earth. It is called acid rain.

The acid rain does not care for the natural boundaries of a country. The oxides of sulphur and nitrogen may be emitted in one country and converted into acid rain in another country. The acid rain decreases the soil water and disturbs the growth of plants. It affects the buildings of marbles.

i) It makes the soil river and lakes slightly acidic. ii) The acidic soil leaches the metals like Ai Hg Pb and Ca. iii) The high concentration of AI is harmful for the fish.

Smog is a combination of smoke and fog. It contains high conents of SO₂ and if it has reducing property that it is called reducing smog. Combustion of coal and the chemical reaction of pollutants in the air the source of smog.

Photochemical smog is consisted of high concentration of oxygen like ozone. It is also called oxidizing smog. It is yellowish brown brown grey hazy and has unpleasant odour. The main reactants of photochemical smog are NO and unburnt hydrocarbons.

It builds up the oxidizing agent like H₂O₂,HNO₃ P.A.N is eye irritant and toxic to the plants.

i) There should be sufficient NO hydrocarbons and volatile organic compounds. ii) The movements of air must be little so that the reactions are not disturbed.

Ozone filters most of the harmful U.V rays present in the sunlight. The place where the ozone layer becomes thin is called ozone hole.

It damages eyes agrivates asthema and decre3ases the elasticity of the lung tissues, It increases the coughing and creates chest discomfort. It is harmful for the plants and attacks rubber.

It has low concentration close to the equator. In sub-polar regions its average concentration is 450. D,U. Its concentration also changes with seasons. It has the highest level in the early spring and the lowest in September to November.

It absorbs U.V radiation and increases the temperature on the upper part of the ozone layer. U.V radiation is very dangerous for the living beings.

The following reaction show that how ozone layer is destroyed by chlorofluoro carbon:
CFCI₃………………………………….. CFCI₂+CI
CI+O₃……………………………………….CIO+O₂
CIO+O………………………………………..CI+O₂

i) Live stock waste. ii) Land fills. iii) Agriculture. Iv) pesticides. v) Oil leaks. Vi) Spills. vii) Disposal of industrial effluents. Viii) Water bodies. ix) Septic tanks.

Bacteria is present in the live stock waste. It contaminates the surface and ground water. It cause the diseases like dysentery typhoid and hepatitis.

When petroleum is transported from one place to another then it may be lost on the way due to the one reason or the other. This is called oil spoilage.

Water gets polluted by: i) Accidental oil spills. ii) Leakage from cargo oils tankers. iii) Pipe line leakage. iv) Leakage of underground storage tanks.

Many petroleum products are poisonous and create serious health problems to humans animals and aquatic life.

Detergents are the sodium salts of benzene sulphonates and are used as clearing agents in houses and industries. There are various types of surfactants in the detergents. These are anionic cationic and amphoteric. Most common type  of surfactants are sodium salts of organic sulphonates. They are threat to animal life by decreasing dissolving oxygen in H₂O.

Those substances which directly kill unwanted organisms are controlled by interfering with its reproduction process are called pesticides. There are of three types i.e insecticides herbicides and fungicides.

i) Malaria ii) Yellow fever. iii) Bubonic plague iv) Sleeping sickness.

Pesticides affect the agricultural food products and drinking water. They are all poisonous.

Chlorinated hydrocarbons can create the following problems.
i) Nausea                      ii) Dizziness
iii) Tremors                 iv) Blindness.
v) Skin eruption         vi) Effect on central nervous system.

The following metals are pollutants present in the industrial wastes.
Pb, Cd, Hg, As and Sb. Leather tanneries are Cr salts with Cr⁺⁶ state. These salts of Cr are highly toxic.

It is an abbreviation of biochemical oxygen demand. The value of BOD is the amount of oxygen consumed as a result of biological oxidation of dissolved organic matter in the sample.

It is the abbreviation of chemical oxygen demand COD is the organic contents of water which consumes oxygen during chemical oxidation and it is evaluated by its chemical oxygen demand.

It is determined directly by treating with dichromate ion which is powerful oxidizing agent. The organic matter in the water is oxidized while the remaining dichromate is determined by volumetric method.

There are four stages. i) Aeration to settle down the suspended matter. ii) Precipitation of small particles. iii) Precipitation and removal of solid matter. iv) Treatment of water with chlorine to kill viruses and bacteria.

When H₂S gas is removed some of organic  matter is oxidized. Fe⁺²  ions are oxidized to Fe⁺³  which gives insoluble Fe(OH)₃.

The important coagulating agents are AI₂(SO₄)₃ or potash alums. Geletenous white precipitate of AI(OH)₃ is produced and suspended impurities are absorbed on its surface. More than 80% of suspended impurities can be removed.

Chlorine is passed through water which produces HCIO. It kills the micro-organism by passing through their cell membranes.

Chlorine reacts with NH₃ to give NH₄CI, NHCI₂ and NCI₃. These compounds are powerful eye irritants. Chlorinated water can cause cancer in the bladder and rectum.