Cook IB Option E Chemistry

 The effect of human activity on the environment.  How does it impact:  Air  Water  Soil  3 Key areas of study:  Atmospheric Pollutants  Discarded waste in landfills  Greenhouse gases

 Air is a mixture of the following elements and percentages: Gas% Composition Nitrogen (N 2 )78 Oxygen (O 2 )21 Argon (Ar)1 Water Vapor1-4 Carbon Dioxide (CO2)0.04

 Is a substance that has a harmful effect on the environment and is present in concentrations greater than it natural levels.  Effects depend on  TOXICITY  Length of time they remain in the enviroment  Air pollution is classified as Primary and Secondary  Primary=emitted directly into the atmosphere  Secondary=produced from primary pollutants chemical changes.

 CO 2  Produced from the combustion of fossil fuels  CO  Smog  SO 2  NO  VOC’s (hydrocarbons)  Now its time to discuss the natural and anthropogenic sources.

 CO  Toxic to humans because if affects the uptake of oxygen in blood  Its absorbed by the lungs and binds to hemoglobin which prevents oxygen from binding  Hb + CO  COHb  Hemoglobin + Carbon monxide=  Carboxyhemoglobin  This prevent oxygen from being transported  This colorless and odorless compound can cause dizziness and death at high concentrations  Sources: Anthropogenic =incomplete combustion of fossil fuels and forest fires  2C + O 2  2CO  CO pollution occurs in urban areas with heavy traffic  CO is formed by natural sources during atomspheric oxidation of methane gas.  Methane comes from

 Reducing the amount of CO can be done doing the following:  Lean Burn engines  Catalytic converter:  Thermal Exhaust reactor:

 Follows low air/fuel ratios -(14:15 by mass) is needed for complete combustion  Max power is achieved with mixture richer in fuel, with lower air/fuel ratio around 12.5 by mass, but this makes more CO.  Engines misfire with leaner (lower ratios)  Lean burn engines have ratios 18 or higher

 Control Exhaust emissions  Hot gases are mixed with air and passed over a platinum based catalyst.  Oxidation catalyst are used in lean burn engines to convert CO to CO2.  3 way catalyst work in conventional engines. They oxidize CO to CO2 and hydrocarbons to water and CO2  Review equations on pages 675 HL and 368 SL

 Thermal Exhust Reactors  Take advantage of heat of the exhaust gases and makes CO react with more air to produce CO2  Review Figure 16.2  Know reactions for each CO method of control, both HL and SL.

 catalyst is a substance that causes or accelerates a chemical reaction without itself being affected. Catalysts participate in the reactions, but are neither reactants nor products of the reaction they catalyze.  There are two different types of catalyst at work, a reduction catalyst and an oxidation catalyst. Both types consist of a ceramic structure coated with a metal catalyst, usually platinum, rhodium and/or palladium.

 When an NO or NO 2 molecule contacts the catalyst, the catalyst rips the nitrogen atom out of the molecule and holds on to it, freeing the oxygen in the form of O2. The nitrogen atoms bond with other nitrogen atoms that are also stuck to the catalyst, forming N2. For example:  2NO => N 2 + O 2 or 2NO 2 => N 2 + 2O 2

 The known nitrogen oxides are:  NO (produced from natural decomposition/lightning)  NO 2 (most toxic)  N 2 O  These react with hydrocarbons to form photochemical smog, nitric acid and contribute to acid rain.  Motor vehicles are the main source (fig 16.3)  Only under conditions of high temperatures ( C in automobile engines), nitrogen and oxygen in the air react to form NO.

 NO (Most pollutant)  Produced naturally for decomposition of nitrogen containing compounds  Nitrogen Fixing Bacteria and Lightning  Review reactions of Nitrogen and the nitrogen cycle  N 2 O  Major source is bacteria decomposition  Reacts with hydrocarbons to form photochemical smog and also forms HNO 3 making acid rain

 Lean Burn Engines  A rich mixture with a high fuel content produces low No x, but high CO. Lean burn engines which use air:fuel ratios : 18:1 can be used to reduce emissions of both NO x and CO.  Three way catalytic converters  They oxidize CO to CO 2  2CO + O 2  2CO 2

 There are 2 types:  SO2 and SO3  SO2 is the most dangerous, that can harm people, plants and materials (buildings)  Natural sources: Volcanos and rotting veggies  Secondary Pollutant  Review Reaction  Anthropogenic sources: Fossil Fuels (coal)  Review all reactions

 Pre Combustion:  The best way is to remove sulfur before or after combustion.  Sulfur can be removed by crushing the coal and washing with water. Sulfide sinks to bottom and separates from clean coal.  Review Reaction  Post Combustion  Alkaline scrubbing Figure 16.4  A alkaline mixture is sprayed downward unto exhaust gas. The mixture contains CaO (lime) reacts with SO2 and forms calcium sulfate which is deposited in landfill.  Fluidized Combustion  Coal is mixed with powered limestone on a metal plate as air passes through the mixture which makes particles float above a plate making a mixture behave like a fluid. The heat produced from combustion of coal causes the CaCO3 to break up into CaO and CO2 the SO2 is removed as it combust with coal.  See Reaction

 Solid particles of dust, carbon or liquid droplets of mist or fog.  Have small diameter: micrometers  Very polar and attracted to water and form aerosols.  Gaseous suspension of very small particles of liquid  Examples:  Soot (from incomplete combustion of hydrocarbons and coal burning factories)  Dust  Sulfur from volcanoes  Pollen, bacterial and fungal spores  Arsenic from insecticides  Asbestos  Material containing silicate crystals which is used to insulate building. These are released in the air when buildings are demolished.  Mercury (Fungicides, making of paper and pulp.

 Gravitational Settling by rain and snow  They can be prevented from entering atmosphere by Treating industrial emissions using the following physical methods. -Flitration -Centifugal separation -Settling tanks -Scrubbing -Electrostatic precipitation Review these methods for quiz on weds

 These are organic air pollutants  Methane  Chloroethane  Aromatic hydrocarbons (from incomplete combustion of coal/wood) Benzene VOC’s also released into air from solvents and paints Hydrocarbons from secondary pollutants Halogen organic compounds (CFC’S) Photochemical Smog Methane is released in large amounts by cows. It is produced by bacterial anaerobic decomposition of organic material in the water and soil. Unsaturated hydrocarbons (with double bonds), called trepenes are given out by plants. Anthropogenic sources include: Unburned Petroleum products; Gasoline emitted from car exhaust. Basicaly everything from fossil fuels

 Using Oxidation Catalytic converters  Using Thermal Exhaust Reactors  Review all reactions and methods of control

 Two types of Smog  Photochemical Smog:  From nitrogen oxides which oxidizes in dry sunshine  Pea Soup Smog  Carbon Particulates and SO2  From reducing