Chemistry Project
Group 4
Group members: Chan Hoi Yan (1)
Chan Wing Yan (5)
Lam Lai (19)
Lam Leong Wai (20)
Yim Tin Chee (36)
Unit 46: Chemistry and the Environment
- Define the terms pollution and pollutant.
Ans: Pollution is the introduction of waste matter or energy into the environment by humans. It causes damage or deterioration to living systems and/or the environment. A pollutant refers to any substance or energy produced through human activities which, at an unacceptable level, causes damages to the environment or is harmful to living systems.
- What are the major air pollutants?
Ans: The major air pollutants are carbon monoxide, sulphur dioxide, nitrogen oxides, hydrocarbons, ozone, and particulate.
- What are their sources or formation with the help of equations?
Ans:
Carbon monoxide: The major source of this pollutant is motor car exhaust. It is produced through incomplete combustion of carbon containing fuels, such as petrol, coal and wood. For example, octane bay be burnt incompletely as follows:
C8H18(g) + 9O2(g)→3CO2(g) + 3CO(g) + 2C(s) + 9H2O(l)
Sulphur dioxide: Sulphur dioxide comes mainly from burning fossil fuels (e.g. fuel oil and coal) which contain sulphur. A large proportion of sulphur dioxide is produced during the operations in power stations and metal smelters in which sulphur-containing coal is used as fuel, and also the manufacturing industries in which fuel oil is burnt
Nitrogen oxides: Nitrogen oxides are produced whenever fuels are burnt at a very high temperature. Diesel driven vehicles produces much less carbon monoxide but a lot more nitrogen oxides than petrol engines.
Hydrocarbons: They are formed from the evaporation of organic materials such as petrol, diesel and solvents. They are also found in car exhaust as unburnt hydrocarbons.
Ozone: it is produced by the reaction of oxygen gas with free atoms of oxygen which are formed from the reactions between nitrogen oxides and hydrocarbons in sunlight.
O2(g) + O →O3(g)
Oxygen radical
Particulates: They include black smoke (mainly fine carbon particles), dust and soot (coarse carbon particles). They are produced during the operations in incinerators, factories, diesel vehicles, construction sites and coal or charcoal burners.
- What are the common effects of these pollutants?
Ans:
Carbon monoxide: It reduces the amount of oxygen delivered to body organs and tissues, and can cause death.
Sulphur dioxide: It impairs the respiratory function, aggravate existing respiratory diseases (e.g. bronchitis and asthma) and cardiovascular diseases.
Nitrogen oxides: It irritates the lungs and lower the resistance to respiratory inflections, and causes the formation of photochemical smog and acid rain.
Hydrocarbons: It causes photochemical smog and some are carcinogenic.
Ozone: It affects the respiratory system, increases susceptibility to respiratory inflections and damages plants.
Particulates: It impairs the lung function by hindering gas exchange and damaging lung tissues, and causes respiratory illness.
- What are the factors that the harmful effects of pollutants depend on?
Ans: The harmful effects of pollutants depend on their concentrations and the duration of exposure to them. Take carbon monoxide as an example. If the concentration of it is 600-700 ppm, inhaling it for hours brings about barely detectable effects. However, a concentration of 4000 ppm or higher can cause death in less than an hour. Of an adult is exposed to an atmosphere containing 1000 ppm carbon monoxide for 4 hours, he is likely to die from carbon monoxide poisoning.
- What does ppm stand for?
Ans: “ppm” represents “part per million” which is a unit for expressing concentration. This is the number of molecules of pollutants per million molecules in air. Based on the Avogadro’s law, ppm is also equal to the number of volumes of pollutants per million volumes of air.
- Express 0.03 ppm SO2 as μg m per cube.
Ans: 85.437 μg m per cube.
- Decide whether the unpolluted rainwater is acidic or alkaline? Explain with the help of equations?
Ans: Unpolluted rainwater is slightly acidic, with a pH value of about 5.7. It is because as it falls, the rainwater reacts with carbon dioxide in the air to form carbonic acid.
CO2(g) + H2O(l)→H2CO3(aq)
- What are the two major air pollutants responsible for the formation of acid rain? Write down the relevant equations?
Ans: Acidic gaseous pollutants like sulphur dioxide and nitrogen dioxide are mainly responsible for the formation of acid rain.
For sulphur dioxide:
In the atmosphere, sulphur dioxide is slowly oxidized to sulphur trioxide which dissolves readily in water droplets to dorm sulphuric (VI) acid.
2SO2(g) + O2(g)→2SO3(g)
SO3(g) + H2O(l)→H2SO4(aq)
Sulphuric (IV) acid is also formed when sulphur dioxide dissolves in rainwater.
SO2(g) + H2O(l) →H2SO3(aq)
The sulphuric (IV) acid formed will be further oxidized to Sulphuric (VI) acid by atmospheric oxygen.
H2SO3(aq) + O2(g) →2H2SO4(aq)
For nitrogen dioxide:
When nitrogen monoxide is released to the atmosphere, it combines with atmospheric oxygen to form nitrogen dioxide.
2NO(g) + O2(g) →2NO2(g)
In a series of complex reactions, nitrogen dioxide combines with oxygen and water vapour to form niric (V) acid.
4NO2(g) + H2O(l) + O2(g) →4HNO3(aq)
- What are the effects of the acid rain on the environment?
Ans: Acid rain causes a lot of harmful effects on the environment. In water of Ph lower than 4.5, calcium metabolism in freshwater fish will be affected, leading to poor health and stunted growth. As a result, the diversity and population of some freshwater species will be reduced. In soil of pH lower than 4.5, absorption of essential nutrients (e.g. K+, Ca2+ and Mg2+) by plants will be affects, resulting in the death of plants.
Acid rain also corrodes metals and accelerates the rate of deterioration of buildings, rocks and statues.
- What does it mean by photochemical smog?
Ans: the word “smog” comes from two words: smoke and fog. It is used to characterize a visible combination of smoke and fog. Photochemical smog is a mixture of pollutants including particulates, nitrogen oxides, ozone, aldehydes, peroxyacetyl nitrate (PAN) and unreacted hydrocarbons, etc.
- How is the photochemical smog formed?
Ans: Reactions that lead to the formation of photochemical smog are irritated by sunlight and involve hydrocarbons and nitrogen oxides emitted from automobiles. The combination of sunlight, particulate matters and abundant pollutants present in modern cities provide favourable condition for smog formation.
Nitrogen dioxide from automobile exhaust first absorbs sunlight and breaks down into nitrogen monoxide and free oxygen atom which is very reactive.
The oxygen atom then reacts with other components of automobile exhaust (e.g. unburnt hydrocarbons) and those of the atmosphere (e.g. oxygen and water vapour) in a series of complex reactions to produce a variety of lachrymatory and toxic chemicals such as peroxyacetyl nitrate (PAN).
The wavelength of ultraviolet radiation from the sun determines which bonds are broken in the reactions that lead to the formation of photochemical smog. Therefore, the reactions vary with altitude.
- What are the effects of the photochemical smog?
Ans: Photochemical smog causes headaches, eye, nose and throat irritation, worsening of the lung function, coughing and wheezing. Ozone attacks the C=C linkage in rubber in a process known as ozonolysis. It can therefore cause rubbers and fabrics to deteriorate and car tyres to crack.
- What is the formula of ozone?
Ans: O3
- What is the formation of the ozone in the lower part of atmosphere?
Ans: In the lower part of the atmosphere (i.e. the troposphere), ozone can be formed in a number of ways: by the reaction between nitrogen oxides and hydrocarbons in sunlight; by electric sparks which occur in car engines and electrical appliances (e.g. photocopiers and electric motors); and by lightning. It can also be formed by passing a stream of oxygen through an electric discharge. However, ozone is very reactive (oxidizing). So, it does not stay in the atmosphere for a long time.
16. What is the formation of the ozone in the stratosphere?
Ans: In the stratosphere, ozone is formed from atmospheric oxygen by absorption of ultraviolet radiation of the right energy (wavelength 250 nm), which dissociates oxygen molecules into free oxygen atoms.
O2 →2O(g)
The oxygen atoms produced react with other oxygen molecules to form ozone.
O(g) + O2)(g) →O3(g)
17. What happen to ozone if it absorbs UV radiation of wavelength length 215 to 295 nm?
Ans: If ozone absorbs UV radiation of wavelength 215 - 295, it undergoes photodissociation and splits up again.
O3(g) →O2(g) + O(g)
18. What is the significance of the above reactions?
Ans: The reaction is responsible for the vital screening effect of ozone. It screens off the harmful ultraviolet radiation. In the stratosphere, ozone is constantly created and destroyed. Therefore, its concentration in the stratosphere remains constant.
19. What are the effects of ozone to human?
Ans: The presence of the ozone layer in the stratosphere is very important for human. The concentration of ozone in the stratosphere is very low, but it is sufficient to filter out 99% of the dangerous ultraviolet radiation from the sun.
20. What would happen if the ozone layer becomes thinner?
Ans: If the ozone layer becomes thinner, it may result in an increase amount of ultraviolet radiation reaching the Earth's surface, leading to an increase in the incidence of skin cancer, genetic mutation, cataract, and a decrease in the yield of crops.
21. What substances would cause a decrease of ozone in the atmosphere?
Ans: Chlorofluorocarbons(CFCs), halons, Tetrachloromethane, 1,1,1-Trichloroethane and Hydrochlorofluoro-carbons(HCFCs) would cause a decrease of ozone in the atmosphere.
22. Using one of the substances in Q21, write down the relevant equations for depletion of
the ozone in the atmosphere.
Ans: CFCs(CCl3F and CCl2F2) is one the substances that causes the thinning of ozone layer, it destroys the ozone by the following reactions :
CCl3F(g)→CCl2F (g) + Cl．(g)
CCl2F2(g)→CClF2(g) + Cl．(g)
The free chlorine radicals (Cl．) from the above initial steps readily react with ozone via the reactions below :
Cl．(g) + O3(g)→ClO．(g) + O2(g)
ClO．(g) + O3(g)→Cl．(g) + 2O2(g)
23. Give some alternatives for CFCs compounds.
Ans: Haloalkanes which are not fully halogenated and they are known as "hydrochlorofluocarbons" (HCFCs) and "hydrofluorocarbons" may be alternatives for CFCs in the industrial field.
Other possible alternatives for CCs are hydrocarbon such as butane and propane. Moreover, Ch3CH2CH3, CH3CH2CH2CH3, CH2Cl2, CH3OCH3 and CH3CHF2are the possible alternatives for CFCs.
Water Pollution :
24. What are the causes of water pollution ?
Ans: Water pollution may be caused by livestock waste, oil spillages, residues of pesticides, detergents in the sewage and industrial effluents.
25. What are the effects of water pollution ?
Ans: The adverse effects of different causes on the environment include :
1. Livestock waste
When there is an excessive amount of organic matter discharged into water, the
exiting micro- organisms will grow and multiply rapidly and oxygen is rapidly
depleted. Because of the lack of oxygen, anareobic micro-organisms begin to partially
break down the organic matter, releasing noxious gases like methane, ammonia
and hydrogen sulphide. As a result, aquatic organisms are endangered.
2. Oil spillages
a) Clog the feathers of sea birds and prevent them from flying or swimming.
b) Interfere with the insulation of the feathers of birds, and cause the death of birds
from cold or pneumonia.
c) Poison birds by ingestion.
d) Prevent dissolution of oxygen, and cause the death of aquatic organisms.
e) Spoil recreational resorts.
3. Residues of pesticides
a) They are non-biodegradable and may accumulate along food chains until a toxic
level is reached.
b) DDT resists degradation and remains in the environment.
c) DDT is very soluble in fat, including the fat in milk and the body fat of animals,
with the potential for damaging internal organs.
d) DDT affects the reproduction of animals.
4. Detergents in sewage
Sewage is domestic waste water. A major pollutant present in sewage is synthetic
detergents. Discharge of detergents causes eutrophication brought by phosphates
found in some detergents. It also causes foaming in rivers and lakes. Ingestion
of detergents by aquatic organisms can cause death.
5. Industrial effluents
They may contain toxic materials such as heavy metals, cyanides and polychlorinated
hydrocarbons. Of particular concern in aquatic environment is the bioaccumulation
of heavy metals. This is a process by which the heavy metals become more and more
concentrated as they move up the food chains.
26. What does DO stand for ?
Ans: DO stands for Dissolved Oxygen.
27. What is the indication of the DO value ?
Ans: DO value indicates the oxygen content in water. It is measured in mg of oxygen per dm-3of water percentage saturation of dissolved oxygen. It can be used to indicate the general water quality.
28. What does BOD stands for ?
Ans: BOD stands for biochemical oxygen demand.
29. What does it mean by five-day BOD ?
Ans: Five-day BOD (BOD5) value is used to indicate the relative oxygen requirements in treating effluents and polluted waters. The water sample is incubated for five days at 20 degree celcius and the amount of oxygen consumed is measured. For example, if a sample has an initial DO of 8mg dm-3, and in five days it has dropped to 2 mg dm-3, then BOD5 = ( 8 - 2 )mg dm-3 = 6mg dm-3.
30. What is the indication of the BOD value ?
Ans: BOD value indicates the extent of organic pollution in water. If the water has a high BOD, this implies that a lot of organic waste is present and much oxygen is required to break the waste. A low BOD indicates the presence of only a small amount of organic matter and there is little organic pollution.
31. What are the major causes of the solid waste?
Ans: Solid waste is produced by the activities of domestic households, commercial and manufacturing industries and construction sires in the territory.
32. How can we dispose solid waste?
Ans: Incineration and landfilling are two common disposal methods for solid waste.
33. What are the advantages and disadvantages of each type of disposal methods of solid waste?
Ans: Incineration has the advantages of reducing the volume of the waste by approximately 85%, killing the disease-causing organisms at high temperature, and having no risk of causing water pollution. However, the main disadvantage of incinerating municipal waste is the potential danger of polluting the atmosphere with toxic chemicals, e.g. sulphur dioxide, carbon dioxide.
In landfilling, the wastes are compressed and covered with earth on landfilling site. The potential environmental problems associated with landfilling result mainly from the generation of landfill gas (mostly methane) and leachate (highly polluting water percolating through decaying waste in landfill). However, landfill gas and leachate can be collected. Methane can be used as an energy source in some countries. Leachate is treated in sewage treatment plant.
34. What are the pollution problems associated with the disposal of plastics?
Ans: As plastics are chemically tailored for long life, they do not generally undergo decomposition in landfill sites. Plastic waste can last for a long time, thus decaying the reuse of the landfill sites. Incineration of plastic waste produces air pollutants such as hydrogen chloride from polyvinyl chloride and other chlorine-containing polymers. The hydrogen chloride produced can cause acid rain which damages the environment. Also, plastic waste in the sea poses direct danger to fishes. Small fishes have been found dead with their digestive tracts clogged by fragments of plastic foam they had ingested. Sea animals have been suffocated to death by plastic bags. The use of certain chemicals such as plasticizers and chlorofluorocarbons in the manufacture of plastics leads to further ecological and environmental problems.
35. How we can solve the pollution problems by solid waste?
Ans:
36. Which department in H.K. is responsible for the pollution control?
Ans: The Environmental Protection Department (EPD) is the principal government department responsible for the pollution control.
37. What are the measures to improve air quality? Describe each of them briefly with the help of equation(s)?
Ans: Installation of catalytic converters in car exhaust systems
The installation of a catalytic converterI the car exhaust system can help reduce the emission of these pollutants. Carbon monoxide is oxidized to carbon dioxide,
Unburnt hydrocarbons is oxidized to carbon dioxide and water, and nitrogen monoxide is reduced to nitrogen. The converter contains precious metals, rhodium and platinum (or palladium), as catalysts. When exhaust gases containing carbon monoxide, unburnt hydrocarbons and nitrogen oxides are passed through the converter, rhodium catalyzes the reduction of nitrogen oxides.
2NO(g) + 2CO(g)--- N2(g) + 2CO2(g)
Platinum catalyzes the oxidation of carbon monoxide and unburnt hydrocarbons such as heptane, C7H16.
2CO(g) + O2(g)----- 2CO2(g)
C7H16(g) + 11O2----- 7CO2(g) + 8H2O(g)
Desulphurization of flue gas
To reduce sulphur dioxide emission, the generating unit of the coal-fired plant in Lamma Island is equipped with a flue gas desulphurization (FGD) system. The FGD system utilizes the ‘wet limestone-gypsum scrubbing process’ which is capable of removing 90% of the sulphur dioxide emitted from the boiler plant when burning coals with a wide range of sulphur contents. Flue gas from the boiler of directed to the absorber which contains a recycled slurry of the limestone for the removal of sulphur dioxide. The calcium sulphate(VI) by the sir blown into the bottom part of the absorber. The chemical reactions of the absorption and oxidation processes can be represented as:
SO2(g) + H2O(l)----- H2SO3(aq) absorption
CaCO3(s) + H2SO3(aq)------ neutralization
CaSO3(s) + CO2(g) +H2O(l)
CaCO3(s) +1/2 O2(g)------CaSO4(s) Oxidation
CaSO3(s) + 1/2H2O(l)------CaSO3·1/2H2O(aq) Crystallization
CaSO4(s) + 2H2O(l)------ CaSO4·2H2O(aq) Crystallization
Installation of low nitrogen oxide burners in power plants
Nitrogen in the sir reacts with oxygen at high temperature near the combustion chamber in a series of complex reactions to form nitrogen monoxide.
N2(g)+O2(g)-----2NO(g)
When released into the atmosphere, nitrogen monoxide reacts with oxygen to form nitrogen dioxide.
2NO(g)+O2(g)---2NO2(g)
Nitrogen oxides formed in this way are known as thermal NOx.
Fossil fuels may contain nitrogen compounds. When these fuels are burnt, the nitrogen compounds are oxidized. Nitrogen oxides formed in this way are known as Fuel NOx
38. What are the measures to improve water quality? Describe each of them Briefly with the help of Equation(s).
Ans: Neutralization of acids and bases