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Environmental Chemistry



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Chapter 14 : Environmental Chemistry



    14.1 Environmental Pollution arrow_upward


  • Environmental pollution is the effect of undesirable changes in our surrounding that have harmful effect on plants.
  • A substance, which causes pollution, is known as pollutant.
  • Pollutants can be solid, liquid or gaseous.

  • 14.2 Atmospheric Pollution arrow_upward


  • The atmosphere that surrounds the earth is not of the same thickness at all heights.
  • The lowest region of atmosphere in which the human beings along with other organisms live is called troposphere.
  • The height of~ 10 km from sea level. Above the troposphere, between 10 and 50 km above sea level lies stratosphere.

  • 14.2.1Tropospheric Pollution

  • The following are the major gaseous and particulate pollutants present in the troposphere:
    • Gaseous air pollutants
    • Particulate pollutants
    1. Gaseous Air Pollutants
  • Oxides of Sulphur: Produced Sulphur containing fossil fuel is burnt. The common species sulphur dioxide is a gas that is poisonous to both animals and plants.
  • Oxides of Nitrogen: Nitrogen dioxide is a lung irritant that can lead to an acute respiratory disease in children. It also harmful to various textile fibres and metals.
  • Hydrocarbon: Composed of hydrogen and carbon only and are formed by incomplete combustion of fuel used in automobiles. It’s carcinogenic.
  • Oxides of Carbon: Carbon Monoxide (CO) is a colorless and odourless gas. Highly poisonous to living beings because its block the delivery of oxygen to the organs and tissues.
  • Acid Rain
  • Normally rain water has a pH of 5.6 due to the presence of H+ ions formed by the reaction of rain water with carbon dioxide present in the atmosphere.
  • When the pH of the rain water drops below 5.6, it is called acid rain.
  • 2. Particulate Pollutants
  • Particulates pollutants are the minute solid particles or liquid droplets in air.
  • These are present in vehicle emissions, smoke particles from fires, dust particles and ash from industries.
  • Smog
  • The word smog is derived from smoke and fog. There are two types of smog:
    • Classical smog
    • Photochemical smog


    1. Classical smog

  • Classical smog occurs in cool humid climate.
  • It is a mixture of smoke, fog and sulphur dioxide.

  • 2. Photochemical smog

  • Photochemical smog occurs in warm, dry and sunny climate.
  • The main components of the photochemical smog result from the action of sunlight on unsaturated hydrocarbons and nitrogen oxides produced by automobiles and factories.                  
  • Ozone Hole
  • Antarctica reported about depletion of ozone layer commonly known as ozone hole over the south pole.
  • It was found that a unique set of conditions was responsible for the ozone hole.
    •                     
  • Sunlight returns to the Antarctica in the spring, the sun’s warmth breaks up the clouds and HOCl and Cl2 are photolysed by sunlight.
  •                             


    14.3 Water Pollution arrow_upward


  • Water is essential for life; pollution of water originates from human activities. though different paths.

  • 14.3.1 Causes of Water Pollution

    • Pathogens
    • Organic Wastes
    • Chemical Pollutants
    Major Water Pollutants:

    Pollutants

    Sources

    Micro-organisms

    Organic Wastes

    Plant Nutrients

    Toxic heavy Metals

    Sediments

    Pesticides

    Radioactive Substances

    Heat

    Domestic sewage

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

    Chemical fertilizers

    Industries and chemical factories

    Erosion of soil by agriculture and strip mining

    Chemicals used for killing insects, fungi and weeds

    Mining of uranium containing minerals

    Water used for cooling in industries



    14.3.2 International Standards for Drinking Water

  • The International Standards for drinking water are given below and they must be followed.
  • Fluoride: For drinking purposes, water
  •     should be tested for fluoride ion    
  •     concentration.
  • Lead: Drinking water gets contaminated with lead when lead pipes are used for transportation of water.

  • 14.4 Soil Pollution arrow_upward


  • Insecticides, pesticides and herbicides cause soil pollution.

  • 14.4.1 Pesticides

  • During World War II, DDT was found to be of great use in the control of malaria and other insect-borne diseases.
  • Pesticides are basically synthetic toxic chemicals with ecological repercussions.
  • Sodium chlorate (NaClO3 ), sodium arsinite (Na3 AsO3 ) such as herbicides most herbicides are toxic to mammals but are not as persistent as organo-chlorides.

  • 14.5 Industrial Wastes arrow_upward


  • Industrial solid wastes are sorted out as biodegradable and non-degradable wastes.
  • Biodegradable wastes are generated by cotton mills, food processing units, paper mills and textile factories.
  • Non-biodegradable wastes are generated by thermal power plants which produce fly ash.

  • 14.6 Strategies to Control Environmental Pollution arrow_upward


  • Controlling environmental pollution by following terms:
    • Waste management: household garbage box beside household discharge.
    • Domestic wastes are collected in small bins.
    • Garbage is sorted out and separated into biodegradable and non-biodegradable materials.
    • Non-biodegradable material such as plastic, glass, metal scraps etc. are sent for recycling.
    • Biodegradable wastes are deposited in landfills and are converted into compost.

    14.7 Green Chemistry arrow_upward


  • Green chemistry is a way of thinking and is about utilizing the existing.
  • Knowledge and principles of chemistry and other sciences to reduce the adverse impact on environment.
  • Green chemistry is a production process that would bring about minimum pollution or deterioration to the environment.
  • Green Chemistry in Day-to-Day Life
  • Dry Cleaning of Clothes: Tetra chlroroethene (Cl2 C=CCl2 ) was earlier used as solvent for dry cleaning.
  • Bleaching of Paper: Chlorine gas was used earlier for bleaching paper
  • Synthesis of Chemicals: Ethanol (CH3 CHO) is now commercially prepared by one step oxidation of ethane in the presence of ionic catalyst in aqueous medium with a yield of 90%.


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