Option D : Environmental Chemistry

The effect of human activity on the environment has become increasingly global, with the effects of chemicals in air and water spanning political and natural borders. An understanding of this impact is essential within and beyond the study of chemistry.

D.1         Primary Air Pollution (3h)

D.1.1     Describe the sources of carbon monoxide, oxides of nitrogen and sulfur, particulates and hydrocarbons in the
              atmosphere.
                    Include both natural and man-made sources. Balanced equations should be used where possible.

D.1.2     Outline the effects of primary air pollution on health.
                    Students should be familiar with at least one harmful effect of each of the substances in D.1.1.

D.1.3     Discuss methods for the reduction of primary air pollution.
                    Limit this to the following methods :
 

  •                 CO - catalytic converters
  •                 NOx - catalytic converters, lean burn engines, recirculation of exhaust gases
  •                 SOx - alkaline scrubbing, removal of sulfur-containing compounds from coal and oil, limestone-based fluidized
  •                 beds
  •                 Particulates - electrostatic precipitation
  •                 Hydrocarbons - catalytic converters.


  • D.2         Ozone Depletion (2h)

    D.2.1     Describe the formation and depletion of ozone by natural processes.
                        Refer to the following equations.
                                O2 2O
                                O2 + O O2
                                O3 O2 + O
                                O2 + O 2O2

    D.2.2     List the pollutants, and their sources, that cause the lowering of ozone concentration.
                        Consider chlorofluorocarbons (CFCs) and nitrogen oxides.

    D.2.3     State the environmental effects of ozone depletion.
                        Include the increased incidence of skin cancer and eye cataracts, and the suppression of plant growth.

    D.2.4     Discuss the alternatives to CFCs in terms of their properties.
                        Alternatives include hydrocarbons, fluorocarbons and hydrofluorocarbons (HFCs). Include toxicity, flammability,
                        the relative weakness of the C-Cl bond and the ability to absorb infrared radiation.

    D.3         Greenhouse Effect and Global Warming (2h)

    D.3.1     Describe the greenhouse effect.
                        Greenhouse gases allow the passage of incoming solar radiation but absorb the heat radiation from the Earth,
                        maintaining a mean global temperature. The greenhouse effect is a normal and necessary condition for life on
                        Earth.

    D.3.2     List the main greenhouse gases and their sources, and discuss their relative effects.
                        The greenhouse gases to be considered are CH4, H2O, CO2 and N2O which have natural and man-made
                        origins.  Their effects depend on their abundance and their ability to absorb heat radiation.

    D.3.3     Discuss the influence of increasing amounts of greenhouse gases on global warming.
                        Effects include climate change, thermal expansion of the oceans and melting of the polar ice caps.

    D.3.4     Outline the influence of particulates on the Earth's surface temperature.
                        Particulates can lower the temperature by reflecting sunlight.

    D.4         Acid Rain (1.5h)

    D.4.1     State what is meant by acid rain and outline its origins.
                        Rain is naturally acidic because of dissolved CO2; acid rain has a pH of less than 5.6.
                        Acid rain is caused by oxides of sulfur and nitrogen. Students should know the equations for the burning of sulfur
                        and nitrogen and for the formation of H2SO3 and H2SO4.

    D.4.2     Discuss the environmental effects of acid rain and possible methods to counteract them.

    D.5         Water Suitable for Drinking (3h)

    D.5.1     Discuss the demand for fresh water and reasons for the inadequacy of its supply.
                        Only a small fraction of the Earth's water supply is fresh water. Of this fresh water, over 80% is in the form of ice
                        caps and glaciers. Water is mainly used for agriculture and industry.

    D.5.2     Compare the advantages and disadvantages of treating drinking water with chlorine and ozone.
                        Include cost, retention time and formation of chlorinated organic compounds.

    D.5.3     Discuss ways to obtain fresh water from sea water using distillation, reverse osmosis and ion exchange.

    D.5.4     Discuss ways to reduce the amount of water used and to recycle water.

    D.6         Dissolved Oxygen in Water (2h)

    D.6.1     Outline the importance of dissolved oxygen in water.

    D.6.2     Outline biological oxygen demand (BOD) as a measure of oxygen - demanding wastes in water.
                        Refer to the amount of oxygen needed to decompose waste matter over a definite period of time. No distinction
                        between biological and biochemical oxygen demand will be made.

    D.6.3     Distinguish between aerobic and anaerobic decomposition of organic material in water.

    D.6.4     Describe the influence of sewage, detergents and fertilisers on the growth of aquatic plants, and the effect of their
                  subsequent decomposition on oxygen concentration (eutrophication).
                        The additional nitrogen and phosphorus compounds encourage growth of aquatic plants often in the form of 'algal
                        blooms' or, in coastal areas, 'red tides'.
     

    D.6.5     Discuss the effect of heat on dissolved oxygen and metabolism in water.

    D.7         Waster Water Treatment (1.5h)

    D.7.1     Outline the primary and secondary stages of sewage treatment and state what is removed during each stage.
                        For primary treatment filtration, flocculation and sedimentation should be covered. For secondary treatment
                        mention the use of oxygen and bacteria (eg. the activated sludge process).

    D.7.2     Discuss the increasing use of tertiary treatment.
                        Include removal of heavy metals and phosphates by chemical precipitation and nitrates by chemical or biological
                        processes.

    D.8         Smog (2h)

    D.8.1         Compare reducing and photochemical smog.

    D.8.2         Describe the catalytic effect of particulates and nitrogen oxides on the oxidation of sulfur dioxide.

  •                     Particulates and SO2 - heterolytic catalysis to form SO3
  •                     NOx + SO2 - free radical catalysis to form SO3
     

    D.8.3         Outline the formation of secondary pollutants in photochemical smog.
                            Treatment should be restricted to the formation of radicals from the reaction of nitrogen oxides with sunlight
                            and the reaction of these radicals with hydrocarbons, leading to the formation of aldehydes and
                            peroxyacylnitrates (PANs).

    D.8.4         Discuss the formation of thermal inversions and their effects on air quality.

    D.9             Ozone Depletion (2h)

    D.9.1         Explain the dependence of O2 and O3 dissociation on the wavelength of light.
                                l = 242 nm l = 330 nm
                                O2 2O O3 O2 + O
                        The energy needed should be related to the bonding in O2 and O3.

    D.9.2         Describe the steps in the catalysis of O3 depletion by CFCs and NOx.
                            For example :

                                    CCl2F2 CClF2 + Cl
                                    Cl + O3 ClO + O2
                                    ClO + O O2 + Cl
                                    NOx similar pathway

    D.9.3         Outline the reasons for greater ozone depletion in polar regions.
                            Consider the seasonal variation in temperature in the upper atmosphere. Refer to surface catalysis on ice
                            particles.

    D.9.4         Describe the properties required for sun-screening compounds.
                            Such compounds should contain conjugated double bonds, eg. paraaminobenzoic acid (PABA), so that
                            absorption of ultraviolet light is possible.

    D.10         Toxic Substances in Water (3h)

    D.10.1      Discuss the different approaches to expressing toxicity.
                            Include the advantages and disadvantages of LD50 (lethal dose in 50% of the population) and maximum daily
                            tolerance.

    D.10.2     State the principal toxic types of chemicals that may be found in polluted water.
                            Include heavy metals, pesticides, dioxins and polychlorinated biphenyls (PCBs).

    D.10.3     Outline the sources, health and environmental effects of cadmium, mercury and lead compounds.

  •                     Cadmium - metal plating, some rechargeable batteries, pigments
  •                     Mercury - seed dressing to prevent mould, batteries
  •                     Lead - some kinds of paint, as tetraethyl lead in gasoline
     

    D.10.4     Describe the sources and possible health effects of nitrates in drinking water.
                            Include the formation of carcinogenic nitrosamines and a possible link to the formation of nitrites leading to
                            oxygen depletion in the body.


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