Chapter 16: Environmental Chemistry

Complete notes for Chapter 16. Covers Air Pollution (Smog, Acid Rain, Ozone Depletion), Water Pollution (BOD, COD, Purification), and Solid Waste Management.

Components of Environment

Atmosphere: Layer of gases (N2, O2, Ar, CO2). Protects from UV, sustains life. Absorbs heat.
Hydrosphere: Water bodies (Oceans 97%, Ice caps 2%, Fresh water 1%).
Lithosphere: Earth's crust (Rocks, Soil). Minerals.
Biosphere: Region capable of supporting life. Ecosystem (Interaction of organisms with environment).

Air Pollution

Primary Pollutants: Direct emission (CO, NOx, SOx, Hydrocarbons).
Secondary Pollutants: Formed by reactions (H2SO4, HNO3, PAN, Ozone).
Carbon Monoxide (CO): Colorless, odorless, toxic. Binds Hemoglobin (Carboxyhemoglobin), reduces O2 transport (Suffocation). Sources: Incomplete combustion, Vehicle exhaust.
Nitrogen Oxides (NOx): NO, NO2. Sources: Combustion, bacterial action. Effect: Acid rain, Smog.
Sulphur Oxides (SOx): SO2, SO3. Sources: Volcanoes, combustion of coal/oil. Effect: Aerosols, Acid rain.

Major Environmental Issues

Acid Rain: pH < 5.6. SOx/NOx + H2O -> H2SO4/HNO3. Effects: Leaches metals (Al, Hg), damages aquatic life, plants, and buildings (Stone leprosy).
Smog:
- Reducing Smog (London): High SO2 + Smoke. Cool/Humid.
- Oxidizing/Photochemical Smog (LA): NOx + Hydrocarbons + Sunlight -> PAN + Ozone. Yellowish. Eye irritation.
Ozone Depletion: Ozone layer (Stratosphere) protects from UV. Destroyed by CFCs (Chlorofluorocarbons) producing Cl free radicals. Cl* + O3 -> ClO* + O2. Hole over Antarctica. Effects: Skin cancer, eye damage.

Water Pollution & Quality

Sources: Livestock waste, Oil spillage, Detergents (Eutrophication), Pesticides, Industrial effluents (Heavy metals: Pb, Cd, Hg, Cr).
Water Quality Parameters:
- DO (Dissolved Oxygen): 4-8 ppm. < 4 ppm is polluted.
- BOD (Biochemical Oxygen Demand): Oxygen consumed by biological oxidation of organic matter.
- COD (Chemical Oxygen Demand): Oxygen consumed by chemical oxidation (Dichromate method).

Water Purification

Treatment of raw water to make it potable:

Aeration: Removes gases, oxidizes Fe/Mn.
Coagulation: Removal of suspended particles using Alum [K2SO4.Al2(SO4)3.24H2O]. Al(OH)3 precipitates impurities.
Disinfection: Killing pathogens (Chlorination). Chlorine forms HCl + HOCl (Hypochlorous acid - kills bacteria). Risk: Chlorinated hydrocarbons (Chloroform - Carcinogenic). Alternatives: Ozone, ClO2.

Solid Waste Management

Landfill: Dumping waste in holes/trenches. Leachate problem.
Incineration: Burning waste at high temp (900-1000°C). Reduces volume. Problem: Toxic emissions (Dioxins). Heat can generate electricity.
Recycling: Reusing materials.
- Paper: Repulping, de-inking.
- Plastic: Reprocessing, Depolymerization, Transformation.

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Chapter 16

chemistry • intermediate 12th