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Environmental Chemistry

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Environmental Chemistry PDF Notes, Important Questions and Formulas

Environmental Chemistry

  1. Environmental pollution: It is the effect of undesirable changes in our surroundings that have harmful effects on plants, animals and human beings.
  2. Pollutant: A substance which causes pollution is known as pollutant.
  3. Pollutants can be solid, liquid or gaseous substances present in greater concentration than in natural abundance.
  4. Pollutantscan be natural or anthropogenic:
    1. Natural pollutants: These are produced due to natural happenings such as volcano eruptions.
    2. Anthropogenic pollutants: These are produced due to human activities.
  5.  Pollutantscan be biodegradable or non-biodegradable:

    1. Biodegradable pollutants: These are pollutants which are rapidly broken down by natural processes. Example: discarded vegetables
    2. Non-biodegradable pollutants: These are the pollutants which are slowly degradable and remain in the environment in an unchanged form for many decades. Examples: DDT, plastic materials, heavy metals, many chemicals and nuclear wastes.
  6. Environmental pollutionis of three types:
    1. Atmospheric pollution.|
      1. Tropospheric pollution.
      2. Stratospheric pollution.
    2. Water pollution.
    3. Soil and land pollution.
  7. Atmospheric pollution occurs when the concentration of a normal component of the air or a new chemical substance added or formed in the air builds up to undesirable proportions causing harm to humans, other animals, vegetation and materials.
  8. Troposphere: The lowest region of atmosphere, in which humans along with other organisms live, is called the troposphere. It extends upto the height of∼10 km above sea level. 
  9. Stratosphere: The stratosphere lies above the troposphere between 10 km and 50 km above sea level. 
  10. Tropospheric pollution: Tropospheric pollution occurs because of two types of pollutants: 

    1. Gaseous air pollutants: These are oxides of sulphur, nitrogen, carbon, hydrogen sulphide, hydrocarbons, ozone and other oxidants.
    2. Particulate pollutants: Particulate pollutants are the minute solid particles or liquid droplets in the air. These are present in vehicle emissions, smoke particles from fires, dust particles and ash from industries. Examples of particulate pollutants are dust, mist, fumes, smoke, smog etc.
  11. Oxides of sulphur as pollutants:

    Sources: Burning of fossil fuels containing sulphur. Harmful effects:

    • These pollutants cause respiratory diseases, e.g. asthma, bronchitis and emphysema in humans.  Sulphur dioxide causes irritation to the eyes, resulting in tears and redness.
    • High concentration of sulphur dioxide leads to stiffness of flower buds which eventually fall off from plants.

  12.   Oxides of nitrogen as pollutants:

    Sources:

    • At high altitudes, when lightning strikes, dinitrogen and dioxygen combine to form oxides of nitrogen.
    •  On burning fossil fuels in an automobile engine at a high temperature, dinitrogen and dioxygen combine to yield significant quantities of nitric oxide (NO) and nitrogen dioxide (NO2).

      N2 (g) + O2 (g) → 1483K 2 NO (g)

      2 NO (g) + O2 (g) → 2 NO2 (g)

    Harmful effects:

    • Damage the leaves of plants and retard the rate of photosynthesis.
    • Nitrogen dioxide is a lung irritant that can lead to an acute respiratory disease in children.
    • It is also toxic to living tissues.
    • Nitrogen dioxide is also harmful to various textile fibres and metals.
       
  13. Hydrocarbons as pollutant

    Source: Incomplete combustion of fuel used in automobiles. Harmful effects:

    • Hydrocarbons are carcinogenic, i.e. they cause cancer.
    • They harm plants by causing ageing, breakdown of tissues and shedding of leaves, flowers and twigs.
  14. Oxides of carbon as pollutant

    a. Carbon monoxide Source:

    • Incomplete combustion of carbon in coal, firewood, petrol, etc.
    • By automobile exhaust.

     Harmful effects:

    It is highly poisonous to living beings because of its ability to block the delivery of oxygen to the organs and tissues. It binds to haemoglobin to form carboxyhaemoglobin, which is about 300 times more stable than oxyhaemoglobin. In blood, when the concentration of carboxyhaemoglobin reaches about 3–4%, the oxygen carrying capacity of blood is greatly reduced. This oxygen deficiency results in causing headaches, weak eyesight, nervousness and cardiovascular disorders. 

    bCarbon dioxide Source:

    • Respiration.
    • Burning of fossil fuels for energy.
    • By decomposition of limestone during the manufacture of cement.
    • By volcanic eruptions.
    • Deforestation.

    Harmful effects:

    • Causes global warming.


  15. Green house effect: About 75% of the solar energy reaching Earth is absorbed by the Earth’s surface, which increases its temperature. The rest of the heat radiates back to the atmosphere. Some of the heat is trapped by gases such as carbon dioxide, methane, ozone, chlorofluorocarbon compounds (CFCs) and water vapour in the atmosphere. Thus, they add to heating of the atmosphere. This causes global warming. 8 This trapping of the Sun’s heat near the Earth’s surface and keeping it warm is called natural greenhouse effect. It maintains the temperature and makes Earth suitable for life. If the amount of carbon dioxide crosses the delicate proportion of 0.03%, then the natural greenhouse balance may get disturbed. This may lead to global warming. 
  16. Green house: In a greenhouse, visible light passes through the transparent glass and heats up the soil and plants. The warm soil and plants emit infrared radiations. Because glass is opaque to infrared (heat) radiations, it partly reflects and partly absorbs these radiations. This mechanism keeps the energy of the Sun trapped in the greenhouse. 
  17. Global warming: An increase in the average temperature of the Earth’s atmosphere (especially a sustained increase that causes climatic changes) which may be caused by additional heat being trapped by the greenhouse gases. 
  18. Acid rain: Normally rain water has PH O 5.6 due to Presence of Hions formed by the reaction of rain water with carbon dioxide present in the atmosphere.

    H2O (l) +CO2 (g) ⇌ H2CO3 (aq)

    H2CO(aq) ⇌ 2H++CO32-

    Source: Burning of fossil fuels, which contain sulphur and nitrogen matter, such as coal and oil in power stations and furnaces or petrol and diesel in motor engines produce sulphur dioxide and nitrogen oxides. SO2 and NO2 after oxidation and reaction with water are major contributors to acid rain because polluted air usually contains particulate matter that catalyses oxidation.

    2SO2 (g) +O2 (g) + 2H2O (l) → 2H2 SO4 (aq)

    4NO2

    Harmful effects:

    • Harmful for agriculture, trees and plants as it dissolves and washes away nutrients needed for their growth.
    • Causes respiratory ailments in humans and animals. o Affects plant and animal life in aquatic ecosystem when acid rain falls and flows as ground water to reach rivers, lakes etc.
    • Corrodes water pipes resulting in leaching of heavy metals such as iron, lead and copper into drinking water.
    • Damages buildings and other structures made of stone or metal. Taj Mahal in India has been affected by acid rain.


  19. Particulates in the atmosphere may be viable or non-viable: 

    1. Viable are minute living organisms that are dispersed in the atmosphere. Examples: Bacteria, fungi, moulds, algae etc.
    2. Non-viable particulates may be classified as
      1. Smoke particulates: They consist of solids or mixture of solids and liquid particles formed during combustion of organic matter.
      2. Examples: Cigarette smoke, smoke from burning of fossil fuel, garbage and dry leaves, oil smoke etc. iii. Dust: They are composed of fine solid particles (over 1 mm in diameter) and produced during crushing, grinding and attribution of solid materials.
      3. Examples: Sand from sand blasting, saw dust from wood works, pulverized coal, cement and fly ash from factories, dust storms etc.
      4. Mists: They are produced by particles of spray liquids and condensation of vapours in air. Examples: Sulphuric acid mist and herbicides and insecticides that miss their targets and travel through air and form mists.
      5. Fumes: They are generally obtained by condensation of vapours during sublimation, distillation, boiling and several other chemical reactions. Generally, organic solvents, metals and metallic oxides form fume particles.


  20. SmogSmoke is a mixture of smoke, dust particles and small drops of fog 
  21. Smog : is two types 

    Classical Smog

    Photochemical Smog

    1. It occurs in cool humid climate

    1.  It occurs in warm, dry and sunny climate.

    2. It is mixture of smoke, fog and sulphur dioxide.

    2 Components of photochemical smog result from the action of sunlight on unsaturated hydrocarbons an oxides of nitrogen produced by automobiles and factories.

    3. It is also called reducing smog

    3. It is also called oxidizing smog



  22. Formation of photochemical smog

    Burning of fossil fuels

    Emission of a variety of pollutants (hydrocarbons and nitric oxide to troposphere)

    At high levels, leads to the chain reaction between pollutants and sunlight

    Chain reaction between pollutants and sunlight

                                 begin mathsize 12px style table attributes columnalign left end attributes row cell 2 NO left parenthesis straight g right parenthesis plus straight O subscript 2 left parenthesis straight g right parenthesis rightwards arrow with sunlight on top 2 NO subscript 2 left parenthesis straight g right parenthesis end cell row cell NO subscript 2 left parenthesis straight g right parenthesis rightwards arrow with sunlight on top NO left parenthesis straight g right parenthesis plus straight O left parenthesis straight g right parenthesis end cell end table end style

                                       O3 (g) +O2 (g) ⇌ O3 (g)

                                       O3(g)+NO(g)→ NO2+O2(g)  

    NO2 and O3 are strong oxidizing agent s and can react with the unbumt hydrocarbons on the polluted air to produce chemical such as formaldehyde, acrolein and peroxyacetyl nitrate (PAN)

     
  23. Effects of photochemical smog: o Ozone and PAN act as powerful eye irritants.

    • Ozone and nitric oxide irritate the nose and throat, and their high concentration causes headache, chest pain, dryness of the throat, cough and difficulty in breathing.
    • Photochemical smog leads to cracking of rubber and extensive damage to plant life.
    • It also causes corrosion of metals, stones, building materials, rubber and painted surfaces.
  24.  Control of photochemical smog: 

    • Use of catalytic converters in automobiles, which prevent the release of nitrogen oxide and hydrocarbons to the atmosphere.
    • Certain plants, e.g. Pinus, Juniparus, Quercus, Pyrus and Vitis can metabolise nitrogen oxide, and therefore their plantation could help in this matter.

  25. Stratospheric pollution is basically due to ozone layer depletion. 
  26. Formation of ozone in stratosphere: 

    begin mathsize 12px style table attributes columnalign left end attributes row cell straight O subscript 2 left parenthesis straight g right parenthesis rightwards arrow with UV on top straight O left parenthesis straight g right parenthesis plus straight O left parenthesis straight g right parenthesis end cell row cell straight O left parenthesis straight g right parenthesis plus straight O subscript 2 left parenthesis straight g right parenthesis rightwards harpoon over leftwards harpoon with UV on top straight O subscript 3 left parenthesis straight g right parenthesis end cell end table end style

  27. Depletion of ozone layer: 

    Release of chlorofluorocarbon compounds (CFCs), which area also known as freons, lead to their mixing with the normal atmospheric gases and eventually reach the stratosphere.

    In Stratosphere

     begin mathsize 12px style table attributes columnalign left end attributes row cell CF subscript 2 Cl subscript 2 left parenthesis straight g right parenthesis rightwards arrow with UV on top straight C with • on top straight l text   end text left parenthesis straight g right parenthesis plus text  F end text subscript 2 straight C with • on top straight l text   end text left parenthesis straight g right parenthesis end cell row cell straight C with • on top straight l left parenthesis straight g right parenthesis plus straight O subscript 3 left parenthesis straight g right parenthesis rightwards arrow with blank on top straight C with • on top straight l left parenthesis straight g right parenthesis plus straight O subscript 2 left parenthesis straight g right parenthesis end cell row cell straight C with • on top lO left parenthesis straight g right parenthesis rightwards arrow with blank on top straight C with • on top straight l left parenthesis straight g right parenthesis text  +O end text subscript 2 left parenthesis straight g right parenthesis end cell end table end style

    This way, the chlorine radicals are continuously regenerated and cause the breakdown of ozone layer.

  28. Ozone hole over Antarctica:

    In summer, nitrogen dioxide and methane react with chlorine monoxide and chlorine atoms forming chlorine sinks.

     begin mathsize 12px style table attributes columnalign left end attributes row cell Cl straight O with • on top left parenthesis straight g right parenthesis plus NO subscript 2 left parenthesis straight g right parenthesis rightwards arrow with blank on top ClONO subscript 2 left parenthesis straight g right parenthesis end cell row cell straight C with • on top straight l left parenthesis straight g right parenthesis plus CH subscript 4 left parenthesis straight g right parenthesis rightwards arrow with blank on top straight C with • on top straight H subscript 3 left parenthesis straight g right parenthesis plus HCl left parenthesis straight g right parenthesis end cell end table end style

    In winter, special type of clouds called polar stratospheric clouds are formed over Antarctica. These polar stratospheric clouds provide surface on which chlorine nitrate formed gets hydrolysed to form hypochlorous acid.

    ClONO2 (g) +H2O→HOCl (g) +HNO3

    It also reacts with produced hydrogen chloride to give molecular chlorine.

    ClNO2 (g) +HCl (g) →Cl2 (g) +HNO3 (g)

    When sunlight returns to Antarctica in spring, the Sun’s warmth breaks up the clouds, and HOCl and Cl2 are photolysed by sunlight.

     begin mathsize 12px style table attributes columnalign left end attributes row cell HOCl left parenthesis straight g right parenthesis rightwards arrow with hν on top straight O with • on top straight H left parenthesis straight g right parenthesis plus straight C with • on top straight l left parenthesis straight g right parenthesis end cell row cell Cl subscript 2 left parenthesis straight g right parenthesis rightwards arrow with hν on top 2 straight C with • on top straight l left parenthesis straight g right parenthesis end cell end table end style

    The chlorine radicals which are formed initiate the chain reaction for ozone depletion.

  29. Effects of depletion of the ozone layer: With the depletion of ozone layer, more UV radiation enters the troposphere. UV radiations lead to

    • Ageing of skin, cataract, sunburn and skin cancer etc. in humans.
    • Killing of many phytoplanktons.
    • Damage to fish productivity.
    • Affect the plant proteins which lead to the harmful mutation of cells.
    • Increases evaporation of surface water through the stomata of the leaves and decreases the moisture content of the soil.
    • Increase in the UV radiations damage paints and fibres, causing them to fade faster.
  30. Water pollution: 

    Major water pollutants

    Sources

    Harmful effects

    Pathogens(microorganisms)

    Domestic sewage

    They cause gastrointestinal diseases.

    Organic wastes (leaves, grass and trash)

    Domestic sewage, animal excreta and waste, decaying animals and plants and discharge from food processing factories

    Lead to decrease in concentration of dissolved oxygen in water and lead to death of aquatic life.

    Plant nutrients

    Chemical fertilizers

     



    Toxic heavy metals(cadmium, mercury, nickel)

    Industries and chemical factories

    Can damage kidneys, central nervous system, liver etc.

    Sediments

    Erosion of soil by agriculture and strip mining

     

    Pesticides(insecticides, herbicides and fungicides)

    Chemicals used for killing insects, fungi and weeds

    Lead to eutrophication.

    Radioactive substances

    Mining of uranium containing minerals

     

    Water

    Water used for cooling in industries

     



  31. Biochemical Oxygen Demand (BOD): The amount of oxygen required by bacteria to break down the organic matter present in a certain volume of a sample of water is called BOD.
  32. Eutrophication: The process in which nutrient enriched water bodies support a dense plant population, which kills animal life by depriving it of oxygen and results in subsequent loss of biodiversity, is known as eutrophication.
  33.   

    Constituent

    Maximum concentration

    Harmful effects of higher concentration

    Fluoride

    1 ppm or 1 mf dm-3

    Causes brown mottling of teeth.

    Lead

    50 ppb

    Can damage kidney, liver, reproductive system etc.

    Sulphate

    500 ppm

    Causes disease such as methemoglobinemia (‘blue baby’ syndrome).

    Nitrate

    50 ppm

    Causes disease such as methemoglobinemia (‘blue baby’ syndrome).

    Metals

     

     

    Fe

    0.2 ppm

     

    Al

    0.05 ppm

     

    Mn

    0.2 ppm

     

    Cu

    3.0 ppm

     

    Zn

    5.0 ppm

     

    Cd

    0.005 ppm

     



  34. Pesticides: They are basically synthetic toxic chemicals with ecological repercussions.  
  35. Herbicides: They are used to kill weeds or undesirable vegetation. Examples: sodium chlorate (NaClO3) and sodium arsinite (Na3AsO3). 
  36. Strategies to control environment pollution:

    1. Water Management 

      Segregate the water as biodegradable and non-biodegradable waste:

      • Biodegradable waste: 
        a. Generated by cotton mills, food processing units, paper mills, and textile factories.
        b. Management: They are deposited in landfills and are converted into compost.
      • Non-biodegradable water:

        a. Generated by thermal power plants which produce fly ash, integrated iron and steel plants which produce blast furnace slag and steel melting slag

        b. Management:

        -Recycling

    2. Toxic wastes are usually destroyed by controlled incineration.
    3. Green chemistry: Green chemistry is a strategy to design chemical processes and products which reduces or eliminates the use and generation of hazardous substances. The chemical reactions should be such that the reactants are fully converted into useful environmental friendly products by using an environment friendly medium so that there would be no chemical pollutants introduced in the environment. 

  37. Green chemistry in daily life:

    Purpose

    Earlier

    Now

    Dry cleaning of clothes

    Tetrachloroethene

    (Cl2C=CCl2) Which contaminates ground water

    Liquefied carbon dioxide with a suitable detergent

    Bleaching of paper

    Chlorine gas

    Hydrogen peroxide (H2O2)with suitable catalyst

     
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