Option E: Environmental Chemistry (SL)

E1 Air Pollution

E.1.1 Describe the main sources of carbon monoxide (CO), oxides of nitrogen and sulfur, particulates and volatile organic compounds in the atmosphere.

Primary Pollutant	Natural Source	Man-made (anthropogenic) source
Carbon Monoxide	Incomplete oxidation of methane	Incomplete combustion of fossil fuels
Oxides of Nitrogen	(1) Electric storms (2) biological processes	Reaction inside internal combustion engines at high temperature
Sulfur Dioxide	(1)   Oxidation of H2S produced by volcanoes (2)   decay of organic matter	(1)   Combustion of sulfur-containing coal (2)   smelting of sulfide ores
Partiulates	Soot, ash, dust asbestos, sand, smoke, pollen, bacterial and fungal spores	Burning of fossil fuels, particularly coal and diesel
Volatile organic compounds	Plants emit unsaturated hydrocarbons terpenes (e.g. rice)	(1)   Unburned or partially burned gasoline and fuels (2)   Solvents.

E.1.2 Evaluate the current methods for the reduction of air pollution.

Primary Pollutant	Method	Explanation
Carbon Monoxide	(1)     Catalytic converters	(1)     A catalytic convertor containing platinum, palladium or rhodium. 2CO + 2NO —Pt→ 2CO­2 + N2
Oxides of Nitrogen	(1)     Catalytic converters (2)     Control of fuel/air ratio	(1)     A catalytic convertor containing platinum, palladium or rhodium. 2CO + 2NO —Pt→ 2CO­2 + N2 (2)     Less air in the engine means lower temperature, so less of oxides of nitrogen is made.
Sulfur Dioxide	(1)     Alkaline scrubbing (2)     Limestone-based fluidized beds	(1)     Sulfur dioxide can be removed from the exhaust fumes by alkaline “scrubbing.” CaCO3(s) + SO2(g) → CaSO­3(s) + CO2(g) CaO(s) + SO2(g) → CaSO3(s) 2CaSO3(s) + O2(g) + 4H2O → 2CaSO4∙2H2O(s) However, this still makes sludge which has to be stored at a landfill or used in the manufacture of plasters. (2)     Burning the coal on a bed of limestone. Limestone decomposes: CaCO3(s) → CaO(s) + CO2(g) and reacts with sulfur oxides CaO(s) + SO2(g) → CaSO3(s); 2CaO(s) + 2SO2(g) + O2(g)  → 2CaSO4(s)
Particulates	(1)   electrostatic precipitation	(1)     Used with particles that do not settle under the force of gravity. Particles are charged and then attracted by oppositely charged electrodes. The material that gets attached to the electrodes is periodically shaken off into a precipitator.
Volatile organic compounds	(1)   Catalytic convertor	(1)     VOCs such as unburned fuel are completely oxidized in a reaction catalyzed by rhodium, palladium or platinum. VOC + O2 → CO2 + H2O

E2 Acid Deposition

E.2.1 State what is meant by the term acid deposition and outline its origins.

Acid deposition is the process by which acidic particles, gases and precipitation leave the atmosphere. Acid deposition can be wet, the acidic species are dissolved in rain, snow or fog, or dry, whereby the acidic chemicals leave the atmosphere as solids or gases.

Pure rainwater usually contains dissolved carbon dioxide, so is acidic with a pH of 5.6. Therefore, acid rain has pH lower than 5.6. This acidity is caused by oxides of sulfur and nitrogen.

Reactions we need to know:

Burning of sulfur and nitrogen:

S(s) + O2(g) → SO2(g) 2SO2(g)  + O2(g)  → 2SO3(g)

N­2(g) + O2(g) → 2NO(g) 2NO(g) + O2(g) → 2NO2(g)

Oxides of sulfur and nitrogen with water:

SO2(g) + H2O(g) → H2SO3(aq) SO3(g) + H2O(g) → H2SO4(aq)

NO(g) + H2O(g) → HNO2(aq) NO2(g) + H2O(g) → HNO3(aq)

We need to know the origins of acid deposition. For sources of oxides of sulfur and nitrogen see E.1.1!

E.2.2 Discuss the environmental effects of acid deposition and possible methods to counteract them.

Environmental effects:

1. Acid rains leach Mg²⁺ from the soil, which reduces chlorophyll levels. This slows growth of the affected plants.
2. Acid rains increase the concentration of Al³⁺ by releasing it from the rock. Al³⁺ binds to the roots and hinders plants from taking up water.
3. Acid rains cause chemical erosion of stones such as limestone (CaCO₃).
4. Acid rains kill aquatic life. Bellow pH 4, lakes are essentially dead.
5. Acid rains leach nutrients from the soil (Mg²⁺, K⁺, Ca²⁺).

Possible methods to counteract acid rain:

1. Ways of reducing SO_x and NO_x in the air are alkaline scrubbing, limestone-based fluidized beds and catalytic converters.
2. Acidity of lakes can be neutralized by adding weak bases CaO and Ca(OH)₂

E3 Greenhouse effect

E.3.1 Describe the greenhouse effect.

Greenhouse gases (esp. CO­₂ and H₂O) let the high-energy short-wave radiation from the sun pass through the atmosphere and hit the earth. Some waves are re-radiated back into the space as higher-wavelength radiation (esp. IR). However, the bonds in greenhouse gases absorb the radiation coming from the earth and re-radiate it back. As a result, Earth and its atmosphere heat up.

E.3.2 List the main greenhouse gases and their sources, and discuss their relative effects.

Gas	Source	Heat trapping effectiveness compared to CO2	Contribution to increased global warming
H2O	(1)   Evaporation of oceans (2)   Combustion of hydrocarbons	0.1	Less than 1%
CO2	(1)   Combustion of fossil fuels and biomass (2)   Forest fires (3)   Decay of plants and animals	1	50%
CH4	(1)   Anaerobic decay of organic matter caused by intensive farming (2)   Naturally released by rice plant	30	18%
N2O	(1)   Bacterial action (2)   Fertilizers	150	6%
CFCs	(1)   Refrigerants (2)   Propellants	10,000 – 25,000	14%

E.3.3 Discuss the influence of increasing amounts of greenhouse gases on the atmosphere.

1. Melting of the polar ice cap and thermal expansion of the oceans (above 4 ̊C) cause increase in the sea levels.
2. Weather patterns change and cause more frequent floods, droughts, changes in precipitation and the yield and distribution of commercial crops. 
3. Availability of fresh drinking water may become a problem.
4. Due to the warmer climate, pests and disease-carrying organisms that like warmth spread to larger areas – the expanse of malaria.

E6 Water Treatment

E.6.1 List the primary pollutants found in waste water and identify their sources.

Primary water pollutant	Source
Pesticides – herbicides, DDT	Farming
Dioxins . accumulate in fatty tissue and extremely toxic	Waste material containing organochlorine that wasn’t incinerated at a sufficiently high temperature.
Polychlorobiphenyls (PCBs)	Transformers, capacitors
Heavy metals	Cadmium from zinc mining, rechargeable batteries and some paints. Mercury from batteries, mercury thermometers and fungicides for seed dressing. Lead from leaded gasoline (lead tetraethyl), old paints and lead water pipes.
Nitrates – soluble in water so hard to remove	Animal farming; artificial fertilizers