The Atmosphere and Environment

Learning Goals Students will describe the volume composition of gases present in dry air as 79% nitrogen, 20% of oxygen and the remainder being noble gases (with argon as the main constituent) and carbon dioxide.

Air Mixture of gases Composition of air Dry clean air : 79% nitrogen 20% oxygen Remainder being noble gases (with argon as the main constituent) and carbon dioxide Water vapour - variable

Fractional distillation of liquid air Dust free air is pumped into the plant Carbon dioxide is removed by bubbling through an alkali NaOH(aq) + CO 2 (g) -> Na 2 CO 3 (aq) + H 2 O (l) Water is removed in a drying tower Gases are compressed to 200 atm Expansion of gases Repeated compression and expansion of gases until temperature reaches -200 0 C Liquid air to a fractionating tower

Fractional distillation of liquid air Air Cooling and compression Liquid air Fractional distillation Nitrogen bp -196 0 C Argon bp -186 0 C Oxygen bp -183 0 C

Components of liquid air and their boiling points gas Boiling point ( 0 C) xenon -108 Krypton -152 Oxygen -183 Argon -186 Nitrogen -196 neon -246 helium -269

Laboratory Preparation of oxygen water oxygen Hydrogen peroxide H 2 O 2 & MnO 2 2H 2 O 2 (aq) -> O 2 (g) + 2H 2 O (l) Powdered manganese (IV) oxide is used as a catalyst

Test for Oxygen gas Oxygen gas Oxygen gas relights a glowing splint.

Uses of Oxygen 1. Used in cylinders for life support : Hospitals ambulances Divers (mixture of oxygen and helium) Astronauts Passenger aircraft carry oxygen (high altitude; air pressure low; cabin is pressurised)

Uses of Oxygen 2. Rockets carry their own oxygen for burning fuel; either liquid oxygen or oxygen in compounds. 3. Making of steel – oxygen gas to burn off impurities

Uses of Oxygen 4. Oxy-acetylene flame – torch to weld iron and steel; cut metals (3500 0 C) 5. Treatment of sewage – oxygen kills harmful bacteria

Bunsen burner flame Pale blue flame (non-luminous): (Complete combustion) CH 4 + 2O 2 -> CO 2 + 2H 2 O Yellow flame (luminous flame) (Incomplete combustion) 2CH 4 + 2O 2 -> 2CO + 4H 2 O CH 4 + O 2 -> C + 2H 2 O

Reaction of certain metals with oxygen Element Equation pH in solution potassium 4K(s) + O 2 (g) -> 2K 2 O (s) 13-14 sodium 4Na(s) + O 2 (g) -> 2Na 2 O(s) 13-14 magnesium 2Mg(s) + O 2 (g) -> 2MgO(s) 8 iron 3Fe(s) + 2O 2 (g) ->Fe 3 O 4 (s) insoluble copper 2Cu(s) + O 2 (g) -> 2CuO (s) insoluble

Properties of oxide in period 3 Group I II III IV V VI VII Element Na Mg Al Si P S Cl Oxide Na 2 O MgO Al 2 O 3 SiO 2 P 2 O 5 SO 2 Cl 2 O Bonding ionic ionic Ionic covalent covalent covalent covalent State solid solid solid solid solid gas gas nature basic basic amphoteric acidic acidic acidic acidic

Reaction of certain non-metals with oxygen Element Equation pH in solution phosphorus 4P(s) + 5O 2 (g) -> 2P 2 O 5 (s) phosphorus pentoxide Phosphoric acid 3 sulphur S(s) + O 2 (g) -> SO 2 (g) Sulphurous acid 3 carbon C(s) + O 2 (g) -> CO 2 (g) Carbonic acid 5

Learning Goals Students will name some common atmospheric pollutants listed below: carbon monoxide, methane, nitrogen oxides (NO, NO 2 ), ozone, sulfur dioxide, unburnt hydrocarbons

Learning Goals Students will be able to state the sources of pollutants as CO: incomplete combustion of carbon-containing substances Nitrogen oxides: lightning activity and internal combustion engines Sulfur dioxide: volcanoes and combustion of fossil fuels, containing sulfur.

Air Pollution What is air pollution? Air that has chemicals that harm living things or damage non-living things. What are air pollutants? Solid particles and poisonous gases in the air.

Air Pollutants 1. Particulates 2. Carbon monoxide 3. Oxides of nitrogen 4. Sulphur dioxide 5. Ozone & CFCs 6. Unburnt hydrocarbon Methane Photochemical smog

Air pollutants Source Effects on health and environment Prevention 7. Carbon cycle 8. Greenhouse gases

Air Pollutants Source : Where does it comes from? Effects : How does it affect the health of people and the environment? Prevention : What measures can be taken to stop that pollutant from coming into the air?

Particulates Source : Ground : earth moving eqiupment, construction work and wind Forest fires and volcanoes Effect : Irritates the lungs Produce haze (reduce visibility)

Particulates Prevention : Prohibition of the use of open fires for the disposal of domestic and industrial waste

Carbon monoxide Source : Incomplete combustion of fuel/petrol in motor vehicle engines. Effect : i) Dangerous – it is colourless and odourless, giving no warning to its presence.

Carbon monoxide Effect : ii. Poisonous – CO is absorbed by haemoglobin in the blood: Haemoglobin + CO -> carboxyhaemoglobin This prevent the blood from transporting oxygen around the body.

Carbon monoxide Effect : iii. At lower level – it causes headaches fatigue and impaired judgement. Prevention: Motorcars fitted with catalytic converters . Exhaust gases pass over a platinum and rhodium catalyst. 2CO + O 2 -> 2CO 2

Sulfur dioxide Source : i. Burning of coal and petroleum (fossil fuel) S + O 2 -> SO 2 ii. Extraction of metals iii. Volcanic eruptions

Sulfur Dioxide Effect : i. irritates the eye and attack lungs, causing breathing difficulties ii. Forms acid rain Sulfur dioxide reacts with oxygen and water in the air to form sulfuric acid 2SO 2 + O 2 + 2H 2 O -> 2H 2 SO 4 SO 2 + H 2 O -> H 2 SO 3

Sulfur Dioxide Effects of acid rain: Corrodes limestone/marble buildings and metal structures It makes water in lakes and rivers acidic , killing fish and other aquatic life. Acidic soil destroys trees and other vegetation.

Sulfur dioxide Prevention Remove sulfur from fossil fuels before burning - too expensive and technologically difficult Flue gas desulfurisation - removal of sulfur dioxide from waste gases

Oxides of Nitrogen Source: Car exhaust fumes At high temperature (in the car engine): N 2 (g) + O 2 (g) -> 2NO (g) nitric oxide More oxygen 2NO(g) + O 2 (g) -> 2NO 2 (g) Also occur during thunderstorms (lightning) and forest fires.

Oxides of Nitrogen Effects: Forms acid rain (nitric acid) 4NO 2 (g) + 2H 2 O(g) + O 2 (g) -> 4HNO 3 (aq) Prevention: Motor cars are fitted with catalytic converter on the exhaust. 2NO(g) + 2CO(g) -> N 2 (g) + 2CO 2 (g)

Unburnt Hydrocarbon Source: From petrol, octane C 8 H 18 Insufficient oxygen present or insufficient time in the cylinders for all the hydrocarbons to be burnt completely

Unburnt Hydrocarbon Effects: Combine with nitrogen oxides to form compounds responsible for photochemical smog . Prevention: Design engines that use more oxygen for combustion of the fuels.

Learning Goals Students will be able to describe the reactions in possible solutions to the problems arising from some of the pollutants. the redox reaction in catalytic converters to remove combustion of pollutants The use of calcium carbonate to reduce the effect of acid rain and in flue gas desulfurisation.

Catalytic Converters Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. A catalytic converter is attached to the exhaust system of a car. It contains the catalysts platinum and rhodium.

Reactions in Catalytic Converter The converter uses two different types of catalysts, a reduction catalyst and an oxidization catalyst. The reduction catalyst is the first stage of the catalytic converter. It uses platinum and rhodium to help reduce the NOx emissions. 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 O 2 .

Reactions in Catalytic Converter The oxidation catalyst is the second stage of the catalytic converter. It reduces the unburned hydrocarbons and carbon monoxide by burning (oxidizing) them over a platinum and palladium catalyst. This catalyst aids the reaction of the CO and hydrocarbons with the remaining oxygen in the exhaust gas.

Chemical Equations in Catalytic Converter Word Equation: Nitric oxide + carbon monoxide  nitrogen + carbon dioxide 2NO (g) + 2CO (g)  N 2 (g) + 2CO 2 (g) Word Equation: Octane + oxygen  carbon dioxide + water vapour 2C 8 H 18 (g) + 25O 2 (g)  16CO 2 (g) + 18H 2 O (g)

Learning Goals Students will be able to describe the reactions in possible solutions to the problems arising from some of the pollutants. The use of calcium carbonate to reduce the effect of acid rain and in flue gas desulfurisation.

Flue Gas Desulfurisation The waste gases are called flue gases. The process of removing sulphur dioxide from flue gases is called desulphurisation.

Flue Gas Desulfurisation CaCO 3 (aq) + SO 2 (g) -> CaSO 3 (s) + CO 2 (g) The calcium sulfite is oxidised to calcium sulfate by air. 2. 2CaSO 3 (s) + O 2 (g) -> 2CaSO 4 (s) Calcium oxide can also be used. CaO(s) + SO 2 (g) -> CaSO 3 (s)

Learning Goals Students will discuss the importance of ozone layer and the problems involved with the depletion of ozone by reaction with chlorine containing compounds, chlorofluorocarbon (CFCs)

Ozone A pale blue almost colourless gas with a characteristic smell Source - electrical machines (photocopiers) - photochemical reaction (a chemical reaction that is initiated by sunlight or UV light, forming photochemical smog – hazy brown air)

Ozone Effects High altitude : protects us from harmful UV Low altitude : harmful (irritates eyes, chest and throat) Form photochemical smog:

Ozone Effects Form photochemical smog: NO 2 (g) + O 2 (g) ⇋ NO(g) + O(g) + O 2 (g) O(g) + O 2 (g) ⇋ O 3 (g) - Ozone can further combine with unburnt hydrocarbon to produce peroxyacyl nitrates (PAN) (cause tearing of the eyes)

Chlorofluorocarbon CFCs Source: - Aerosal propellants - Coolant fluids in refrigerators and air conditioners and - Making expanded polystyrene packaging

Chlorofluorocarbon CFCs Effects: - How do CFCs destroy the ozone layer? In the presence of sunlight, CFCs decomposed to form chlorine atoms . - The chlorine atoms react with ozone molecules to form chlorine oxide and oxygen . Cl + O 3 -> ClO + O 2

Ozone layer A thin layer of ozone in the stratosphere (20-50km) acts as a shield , filtering out the harmful UV rays from the sun. The harmful radiation causes skin cancer, genetic mutation and eye damage (cataract)

Learning Goals Students will be able to describe the carbon cycle in simple terms, to include The processes of combustion, respiration and photosynthesis How the carbon cycle regulates the amount of carbon dioxide in the atmosphere.

Carbon Cycle Atmospheric carbon dioxide respiration photosynthesis Combustion / burning of fossil fuels + volcanic activity

Learning Goals Students will be able to state that CO 2 and CH 4 are greenhouse gases and may contribute to global warming, give the sources of these gases and discuss possible consequences of an increase in global warming

The Greenhouse Effect Greenhouse gases: Carbon dioxide CO 2 Methane CH 4 Nitrous oxide N 2 O They absorb infrared radiation and thus reduces the amount of heat energy escaping into space : global warming.

Methane Source: - Bacterial decay of vegetable matter trapped in low-lying wetlands and stagnant water. - decaying dung and rubbish buried in landfills

Methane Effects: - In strong sunlight, methane and unburnt hydrocarbons can react with nitrogen dioxide to form photochemical smog. - Help trap heat from the sun greenhouse effect or global warming .

The Greenhouse Effect Effects: - decrease in crop yield. (areas with vegetation may become deserts) - floods due to melting of ice in North and South poles. - droughts resulting in food shortage.

Water pollution Industrial waste Untreated sewage Fertilisers Detergents Litter 9. Water pollution 10. Prevention of water pollution

Prevention of Water pollution Purification Desalination New water

The Atmosphere and Environment

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