Environmental chemistry


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Environmental chemistry

  1. 1. 1
  3. 3. •INTRODUCTION •The term “Environment” literally means “surrounding”. It comprises of the following four major components: (1) Atmosphere, (2) Hydrosphere, (3) Lithosphere and (4) Biosphere. • “ENVIRONMENT CHEMISTRY” is a branch of science which deals with the chemical phenomena occurring in the environment, i.e., study of origin, transport, reactions, effects and fates of chemical species in the environment. 3
  4. 4. •Environment Pollution noun [puh-loo-shuhn] •“Environment pollution” is the effect of undesirable changes in our surroundings that have harmful effects on the plants, animals and human beings. A substance, which causes pollution , is known as “pollutant”. Pollutants can be solid, liquid or gaseous substances present in the greater concentration than in natural abundance and are produced due to human activities or due to natural happenings. 4
  5. 5. ATMOSPHRIC POLLUTION Air pollution is defined as the addition of undesirable materials into the atmosphere either due to natural phenomena or due to human activity on the earth which adversely affect the quality of the air and hence affects the life on the earth. It is also known as “Atmospheric Pollution” Atmospheric pollution is generally studied as Tropospheric and Statospheric pollution. 5
  6. 6. •Tropospheric Pollution •Tropospheric pollution occurs due to the presence of undesirable solid or gaseous particles in the air. The following are the major gaseous and particulate pollutants present in the troposphere: 1.Gaseous air pollutants: These are oxides of sulphide, hydrocarbons, ozone and other oxidants. 2.Particulate pollutants: These are dust, mist, fumes, smoke, smog etc. 6
  7. 7. 1.Gaseous Air Pollutants (a) Oxides of Sulphur Oxides of sulphur are produced when sulphur containing fossil fuel is burnt. The most common species, sulphur dioxide, is a gas that is poisonous to both animals and plants. It has been reported that even a low concentration of sulphur dioxide causes respiratory diseases. However, the presence of particulate matter in polluted air catalysts the oxidation of sulphur dioxide to sulphur trioxide. 2SO2 (g) + O2 (g) → SO3 (g) SO2 (g) + O3 (g) → SO3 (g) + O2 (g) SO2 (g) + H2O2 (l) → H2SO4 (as) 7
  8. 8. (b) Oxides of Nitrogen Dinitrogen and dioxygen are the main constituents of air. These gases don’t react with each other at a normal temperature. At high altitudes when lightning strikes, they combine to form oxides of nitrogen. NO2 is oxidized to nitrate ion. When fossil fuel is burnt, dinitrogen and dioxygen combine to yield significant quantities of nitric oxide (NO) and nitrogen dioxide (NO2). N2 (g) + O2 (g) → 2NO (g) [at 1483K] 2NO (g) + O2 (g) → 2NO2 (g) NO (g) + O3 (g) → NO2 (g) + O2 (g) 8
  9. 9. (c) Hydrocarbons Hydrocarbons are composed of hydrogen and carbon only and are formed by incomplete combustion of fuel used in automobiles. Hydrocarbons are carcinogenic, i.e., they cause cancer. They harm plants by causing ageing, breakdown of tissues and shedding of leaves, flowers and twigs. (d) Oxides of Carbon (i) Carbon monoxide: Carbon monoxide is one of the most serious air pollutants. It is a colorless and odorless gas, highly poisonous to living beings because of its ability to block the delivery of oxygen to the organs and tissues. It is mainly released by automobiles. It binds to haemoglobin to form carbonhaemoglobin, which is about 300 times more stable than the 9 oxygen-haemoglobin complex. This results in headache,
  10. 10. weak eyesight, nervousness and cardiovascular disorder. (ii) Carbon dioxide: Carbon dioxide is released into the atmosphere by respiration, burning of fossil fuels for energy, and by decomposition of limestone during the manufacture of cement. Normally it is about 0.03% by volume of the atmosphere. Green plants need carbon dioxide for photosynthesis and they, in turn, emit oxygen, thus maintaining the delicate balance. The increase in mount of carbon dioxide in the air is mainly responsible for global warming. 10
  11. 11. •Global Warming& Greenhouse Effect • • About 75% of the solar energy reaching the 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 like carbon dioxide, methane, ozone, chlorofluorocarbon compounds (CFCs) and water vapour in the atmosphere. Thus, they add to the heating of the atmosphere. This causes “Global Warming”. Just as the glass in a greenhouse holds the sun’s heat near the earth’s surface and keeps it warm. This is called natural greenhouse effect. 11
  12. 12. Causes of Global Warming •Increase in concentration of carbon dioxide which is emitted by automobiles, industries, etc,. •Increase in concentration of methane which is emitted when vegetation is burnt, paddy fields, coal mines etc,. •Increase in concentrations of CFCs which is commonly produced or emitted by refrigerators, A.C.s, etc,. 12
  13. 13. ACID RAIN • • • We are aware that normally rain water has a pH of 5.6 due to presence of Hydrogen ions formed by reaction of rain water with carbon dioxide present in the atmosphere. H2O (l) + CO2 (g) ↔ H2CO3 (aq) H2CO3 (aq) ↔ H+ (aq) + HCO3− (aq) When the pH of the rain water drops below 5.6, it is called acid rain. Oxides of sulphur and nitrogen in the atmosphere produces acid rain. Burning of fossil fuels such as coal and oil in power stations or petrol and diesel in motor engines produce SO2 and NO2 after oxidation and reaction with water are major contributors to acid rain. 2SO2 (g) + O2 (g) + H2O (l) → 2H2SO4 (aq) 13
  14. 14. • 4NO2 (g) + O2 (g) + H2O (l) → 4HNO3 (aq) • Results of Acid Rain • • Acid rain is harmful for agriculture, trees and plants as it dissolves and washes away nutrients needed for their growth. It causes respiratory ailments in human beings and animals. When acid rain falls and flows as ground water to reach rivers, lakes etc. it affects plants and animal life in aquatic ecosystem. It corrodes water pipes resulting in the leaching of heavy metals such as iron, lead and copper into drinking water. 14
  15. 15. 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. Particulates in the atmosphere may be viable or non-viable. The viable particulates e.g., bacteria, fungi, moulds, algae etc., are minute living organisms that are dispersed in the atmosphere. They cause plant diseases. • Non-viable particulates can be classified according to their size and nature as follows: (a) Smoke particulate consist of solid and liquid particles formed during combustion of organic matter. Ex. Cigarette and oil smoke. 15
  16. 16. (b) Dust is composed of fine solid particles, produced during crushing, grinding and attribution of solid materials. Sand from sand blasting, saw dust from wood works, cement and fly ash from factories etc. (c) Mists are produced by particles of spray liquids and by condensation of vapours in air. (d) Fumes are generally obtained by the condensation of vapours during sublimation, distillation, boiling and several other chemical reactions. • The effect of particulate pollutants are largely dependent on the particle size. Air borne particles are dangerous for human health. 16
  17. 17. •SMOG •The word smog is derived from smoke and fog. This is the most common example of air pollution that occurs in many cities throughout the world. There are two types of smog: (a) Classical smog occurs in cool humid climate. It is the mixture of smoke, fog and sulphur dioxide. Chemically it is a reducing mixture and so it is also called as reducing smog. (b) Photochemical smog occurs in warm, dry and sunny climate. The main components result from the action of sunlight on unsaturated hydrocarbons and nitrogen oxides produced by automobiles and factories. 17
  18. 18. Photochemical smog has high concentration of oxidizing agents and is, therefore, called as oxidizing smog. •FORMATION OF PHOTOCHEMICAL SMOG •When fossil fuels are burnt, a variety of pollutants are emitted into the earth’s troposphere. A chain reaction takes place between hydrocarbons and nitrogen oxide in interaction with sunlight and forms nitrogen dioxide. This nitrogen dioxide absorbs energy and breaks up into nitric oxide and free oxygen atom. (i) Oxygen atoms are very reactive and Combines with dioxygen to form ozone (ii) 18
  19. 19. •The ozone formed in the above equation (ii) reacts rapidly with NO (g) formed in equation (i) to regenerate nitrogen dioxide. (iii) •Ozone is a toxic gas and both nitrogen dioxide and ozone are strong oxidizing agents and can react with unburnt hydrocarbons in the polluted air to produce chemical such as formaldehyde, acrolein and peroxidyacetyl nitrate (PAN). •EFFECTS OF PHOTOCHEMICAL SMOG •They damage metals, stones, buildings materials. •Produce irritation in the eyes and respiratory system. 19
  20. 20. •THE OZONE HOLE • In 1980s atmospheric scientists in Antarctica reported about the depletion of ozone layer. In summer season, NO2 and methane react with chlorine monoxide and chlorine atoms forming chlorine sinks, preventing much ozone depletion. In winter season a stratospheric cloud formed providing surface on which chlorine nitrate and gets hydrolyzed to form hypochlorous acid which reacts with hydrogen chloride to form molecular chlorine. 20
  21. 21. EFFECTS OF DEPLETION OF OZONE LAYER • • With the depletion of ozone layer, more UV radiation filters into the troposphere. UV radiations lead to ageing of skin, cataract, sunburn, skin cancer, killing of many phytoplanktons, damage to fish productivity etc. The plant protein gets easily affected which leads to the harmful mutation of cells. Increase in UV radiations damage paints and fibres, causing them to fade faster. 21
  22. 22. •Water Pollution •Water is essential for our life. Without water there would be no life. Pollution of water originates from human activities. Through different paths, pollution reaches surface or ground water. Easily identified source of pollution is called as point source. e.g.., municipal and industrial discharge pipes where pollutants enter the water-source. 22
  23. 23. •Causes of Water Pollution (1)Pathogens: The most serious water pollutants are the disease causing agents called pathogens include bacteria and other organisms that enter water from domestic sewage and animal excreta. (2)Organic wastes: The other major water pollutant is organic matter such as leaves, grass, trash etc. Excessive phytoplankton's growth within water is also a cause of water pollution. • A large population of bacteria decomposes organic matter present in water. They consume oxygen dissolved in water. The amount of oxygen that water can hold in the solution is limited. The concentration 23 of dissolved oxygen is very important for aquatic life.
  24. 24. •If too much organic matter is added to water, all the available oxygen is used up. This causes oxygen dependent aquatic life to die. Thus amount of oxygen required by the bacteria to break down organic matter present in a certain volume of a sample of water is called BIOCHEMICAL OXYGEN DEMAND (BOD). (3) Chemical pollutants: As we know that water is an excellent solvent, water soluble heavy metals such as cadmium, mercury, nickel etc. constitute an important class of pollutants. All these metals are dangerous to humans because our body can’t excrete them. • The organic chemicals are another group of substances that are found in polluted water. Petroleum products pollute many sources of water. 24
  25. 25. •International Standards for Drinking Water •Fluoride: For drinking purpose, water should be tested for fluoride ion concentration. Its deficiency in drinking water is harmful to man and causes diseases such as tooth decay etc. •Lead: Drinking water gets contaminated with lead when lead pipes are used for transportation of water. Lead can damage kidney, liver, reproductive system etc. •Sulphate: Excessive sulphate in drinking water causes laxative effect, otherwise at moderate levels it is harmless. •Nitrate: The max. limit of nitrate in water is 50ppm. Excess nitrate can cause methmoglobinemia (‘blue baby’ 25 syndrome)
  26. 26. Soil pollution or soil contamination is caused by the presence of xenobiotic (human made) chemicals or other alterations in the natural soil and environment.. Causes :  Waste Dumping  Mining Pesticides and Insecticides Urbanization 26
  27. 27. WASTE DUMPING :  Industrial solid wastes and sludge are the major sources of soil pollution  Industrial emissions such as fly ash from thermal power plants can contaminate the surrounding soil.  Nuclear testing laboratories and the increased number of radioactive nuclear reactions can contaminate the soil. Radioactive materials are thriving in the soil for long periods of time, since they often have a long half-life. Strontium-90, for example, a half life of 28 years, and half-life of cesium-137 is 30 years. 27
  28. 28. MINING :  Modern mining projects leave behind disrupted communities, damaged landscapes, and polluted water.  Mining also affects ground and surface waters, the aquatic life, vegetation, soils, animals, and the human health.  Acid mine drainage can cause damage to streams which in return can kill aquatic life.  The vast variety of toxic chemicals released by mining activities can harm animals and aquatic life as well as their habitat.  Mining gas and petroleum also pollutes the land. Petroleum extraction and manufacturing contaminates the soil with bitumen, gasoline, kerosene and mining brine solutions.  Opencast mining, which is a process where the surface of the earth is dug open to bring out the underground mineral deposits, destroys the topsoil and contaminates the area with toxic metals and chemicals. 28
  29. 29. Pesticides :  Many of the chemicals used in pesticides are persistent soil contaminants, which adversely affect soil conservation.  The use of pesticides decreases the general biodiversity in the soil.  The insecticides DDT, methyl parathion and especially pentachlorophenol have been shown to interfere with legumerhizobium chemical signaling. Reduction of this symbiotic chemical signaling results in reduced nitrogen fixation and thus reduced crop yields.  Animals may be poisoned by pesticide residues that remain on food after spraying, for example when wild animals enter sprayed fields or nearby areas shortly after spraying  Widespread application of pesticides can eliminate food sources that certain types of animals need, causing the animals to relocate, change their diet, or starve. Poisoning from pesticides can travel up 29 the food chain and bioacculmulate.
  30. 30. STRATEGIES TO CONTROL ENVIRONMENTAL DAMAGE : The public is becoming increasingly aware that the natural environment is fragile. The recent reports by media have focused on –  Deaths and population declines of birds and fish because of the large oil spills  Deaths of porpoises and whales along the coasts as a result of pollutants and disease;  Fish contaminated with polychlorinated biphenyls (PCBs)  Contamination of rivers and lakes by dioxin and other pollutants that may cause cancer and reproductive disorders. 30
  31. 31. These events may be omens that other forms of life, including people, could become threatened if environmental conditions continue to worsen. But how much worse must conditions be before wildlife and human life are in danger? Or are they in danger already? Clearly, better methods are needed to predict the probability of future environmental and health problems based on present evidence. Such information could guide environmental regulators and decision makers in taking actions in time to minimize damage to the environment and human health. And an important strategy to control such environmental damage is : Waste Management 31
  32. 32. WASTE MANAGEMENT : Waste management is the collection, transport, processing or disposal, managing and monitoring of waste materials. The term usually relates to materials produced by human activity, and is generally undertaken to reduce their effect on health, the environment or aesthetics. Waste management is a distinct practice from resource recovery which focuses on delaying the rate of consumption of natural resources. The management of wastes treats all materials as a single class whether solid, liquid, gaseous or radioactive substances, and tried to reduce the harmful environmental impacts of each through different methods. The two major concepts which are widely used for waste management are :  Waste Hierarchy  Polluter Pays Principle 32
  33. 33. Methods Of Waste Management :  LANDFILL Disposing of waste in a landfill involves burying the waste, and this remains a common practice in most countries. Landfills are often established in abandoned or unused quarries, mining voids or borrow pits. A properly designed and well-managed landfill can be a hygienic and relatively inexpensive method of disposing of waste materials. Older, poorly designed or poorly managed landfills can create a number of adverse environmental impacts such as wind-blown litter, attraction of vermin, and generation of liquid leachate. Design characteristics of a modern landfill include methods to contain leachate such as clay or plastic lining material. Deposited waste is normally compacted to increase its density and stability, and covered to prevent attracting vermin. Many landfills also have landfill gas extraction systems installed to extract the landfill gas. Gas is pumped out of the landfill using perforated pipes and flared off or burnt in a gas engine to generate electricity. 33
  34. 34. AVOIDANCE & REDUCTION METHODS : An important method of waste management is the prevention of waste material being created, also known as waste reduction. Methods of avoidance include : -Reuse of second-hand products -Repairing broken items instead of buying new -Designing products to be refillable or reusable (such as cotton instead of plastic shopping bags) -Encouraging consumers to avoid using disposable products (such as disposable cutlery) -Removing any food/liquid remains from cans -Designing products that use less material to achieve the same purpose (for example, light weighting of beverage cans) Jute bags 34
  35. 35. green chemistry noun [grēn ′kem·ə·strē] It means producing the chemicals of our daily needs using such reactions and chemical processes which neither use toxic chemicals nor emit such chemicals into the atmosphere. 35
  36. 36. •Green chemistry, also called sustainable chemistry, is a philosophy of chemical research and engineering that encourages the design of products and processes that minimize the use and generation of hazardous substances. While environmental chemistry is the chemistry of the natural environment, and of pollutant chemicals in nature, green chemistry seeks to reduce and prevent pollution at its source. •As a chemical philosophy, green chemistry applies to organic chemistry, inorganic chemistry, biochemistry, analytical chemistry, and even physical chemistry. Click chemistry is often cited as a style of chemical synthesis that is consistent with the goals of green chemistry. The focus is on minimizing the hazard and maximizing the efficiency of any chemical choice. •The year 2005 witnessed three key developments in the field of green chemistry: - use of supercritical carbon dioxide as green solvent - aqueous hydrogen peroxide for clean oxidations - use of hydrogen in asymmetric synthesis •Examples of applied green chemistry are : Supercritical water oxidation On water reactions Dry media reactions •The term "Green Chemistry" was coined by Paul Anastas in 1991, who is renowned worldwide as “The Father of Chemistry”. 36
  37. 37. GREEN CHEMISTRY IN DAY-TO-DAY LIFE : Dry Cleaning Of Clothes: Tetra chloroethene (Cl2C=CCl2) was earlier used as solvent for dry cleaning. The compound contaminates the ground water and is also a suspected carcinogen. The process using this compound is now being replaced by a process, where liquefied carbon dioxide, with a suitable detergent is used. Replacement of halogenated solvent by liquid CO2 will result in less harm to ground water. These days hydrogen peroxide(H2O2) is used for the purpose of bleaching clothes in the process of laundry, which gives better results and makes use of lesser amount of water. 37
  38. 38. Bleaching of Paper: Chlorine gas was used earlier for bleaching paper. These days, hydrogen peroxide (H2O2) with suitable catalyst, which promotes the bleaching action of hydrogen peroxide, is used. 38
  39. 39. Synthesis Of Chemicals: Ethanal(CH3CHO) is now commercially prepared by one step oxidation of ethene in the presence of ionic catalyst in aqueous medium with a yield of 90%. CH2=CH2  O2 ethene Catalyst Pd(II)/Cu(II)[in water] CH3CHO (90%) ethanal 39
  40. 40. THANK YOU “The world has achieved brilliance without wisdom, power without conscience. Ours is a world of nuclear giants and ethical infants.” By:- ZEEL PATEL Class:- XI Roll No.:- 1139 40