Chemistry Project
Group I
6S Chan Sin Hang (3)6S Ip Hei Yan (13)
6S Lee Ho Yin (23)6S Leung Tsz Ho (25)
6S Tse Pat Lok (32)6S Wat Choi Choi (34)
Unit 46: Chemistry and the Environment
- Define the terms pollution and pollutant.
Pollution is the introduction of waste matter or energy into the environment by humans. It causes damages or deterioration to living systems and the environment.
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?
Carbon monoxide, sulphur dioxide, nitrogen oxides, hydrocarbons, ozone and particulates are the major air pollutants.
- What are their sources or formation with the help of equations?
Carbon monoxide is formed from incomplete combustion of carbon-containing fuel, for example in the combustion of octane:
C8H18(g) + 9O2(g) 3CO2(g) + 3CO(g) + 2C(s) + 9H2O(l)
Sulphur dioxide is formed from burning of sulphur-containing fossil fuels:
S(s) + O2(g) SO2(g)
Nitrogen oxides are formed whenever fuels are burnt at a very high temperature. For example:
N2(g) + O2(g) 2NO(g)
Hydrocarbons are formed from the evaporation of organic materials such as petrol and diesel. They are also found in car exhaust as unburnt hydrocarbons
Ozone is produced from oxygen gas and free atoms of oxygen. Free atoms of oxygen are formed under sunlight:
O2(g) 2O(g)
Then, the oxygen atom reacts with other oxygen molecules to form ozone:
O(g) + O2(g) O3(g)
Particulates are produced during the operations in incinerators, factories, diesel vehicles, construction sites and coal or charcoal burners. They are solid or liquid particles which are very small.
- What are the common effects of these pollutants?
Carbon monoxide is very poisonous. When one inhales it, it will enter the bloom stream combine with haemoglobin, thus the amount of oxygen delivered to body organs and tissues reduces. This can cause death even in relatively low concentrations.
Sulphur dioxide can cause impairment of the respiratory function, aggravation of existing respiratory diseases (especially bronchitis and asthma) and cardiovascular diseases. Also, sulphur dioxide causes acid rain, which in turn damage buildings cause the deaths of trees.
Nitrogen dioxide, an example of nitrogen oxides gives rises to photochemical smog. It can also irritate the lungs and lower our resistance to respiratory infections such as influenza. Nitrogen dioxide may also impair lung development and it is also a main cause of the formation of acid rain.
Hydrocarbons cause photochemical smog. Some hydrocarbons may cause cancer.
Ozone has a great impact on the respiratory system. Symptoms include cough, chest pain, and throat and eye irritation. Ozone can also increase our susceptibility to respiratory infections and damage plants.
The effect of particulates depends on its size and nature. Very fine particles are the most hazardous as they cannot be filtered out by hairs and mucus in the nose and the respiratory tract. They can be drawn deep into the lungs, where they can remain indefinitely and impair the lung function. They can hinder gas exchange, damage lung tissues and cause respiratory illnesses. Certain particles are suspected to cause cancer.
- What are the factors that the harmful effects of pollutants depend on?
The harmful effects of pollutants depend on their concentrations and the duration of exposure to them.
- What does ppm stand for?
ppm stand for “part per million”. That is the number of molecules of pollutants per million molecules in air.
- Express 0.03 ppm SO2 as µg m-3.
In 1 m-3 of air, there is 0.05/106m3 SO2. Thus by pV = nRT,
p(0.05/106) = n (8.314)T
n = mass of SO2/molar mass of SO2
Thus mass of SO2 = { p(0.05/106)(64) } / 8.314T
If pressure is atmosphere pressure and T is 273K, then
Mass of SO2 in 1m3 air = {101x103(0.05/106)(64) } / 8.314x273 = 142µg m-3
- Decide whether the unpolluted rainwater is acidic or alkaline? Explain with
the help of equations.
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.
Sulphur dioxide and nitrogen dioxide are major pollutants which cause acid rain:
SO2(g) + H2O(l) H2SO3(aq)
This reaction is reversible. The sulphuric(IV) acid will be further oxidized to sulphuric (VI) acid:
H2SO3(aq) + O2(g) 2H2SO4(aq)
On the other hand, sulphur dioxide may convert to sulphur trioxide and the reaction is reversible:
SO2(g) + O2(g) SO3(g)
The sulphur trioxide will form sulphur (VI) acid with rainwater
SO3(g) + H2O(l) H2SO4 (aq)
Nitrogen dioxide will also react with rainwater to form nitric (V) acid:
4NO2(g) + 2H2O(l) + O2(g) 4HNO3(aq)
- What are the effects of the acid rain on the environment?
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 by plants will be affect, 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?
Photochemical smog is a mixture pollutants including particulates, nitrogen oxides, ozone, aldehydes, peroxyacetyl nitrate (PAN) and unreacted hydrocarbons, etc.
- How does photochemical smog formed?
The formation of photochemical smog is due to reactions initiated by sunlight. This involved hydrocarbons and nitrogen oxides emitted from automobiles. For example:
NO2(g) ------> NO(g) + O(g)
UV light
The O atom will react with other components of automobile exhaust and those of the atmosphere in a series of complex reactions to produce a variety of toxic chemicals such as PAN.
Other reactions which cause photochemical smog are listed belong
O(g) + O2(g) O3(g)
O(g) + hydrocarbons aldehydes
O3(g) + hydrocarbons aldehydes
Hydrocarbons + O2(g) + NO2(g) lachrymatory substances, including PAN.
As Photochemical smog is the mixture of the above compounds, obviously ultraviolet radiation from sunlight, particulate matters and pollutants present in big cities are responsible for the photochemical smog.
13. What are the effects of the photochemical smog?
The photochemical smog causes headaches, eye ,nose and throat irritation, worsening of the ling function, coughing and wheezing. And the ozone in the photochemical smog attacks the C=C linkage in rubber in a process called ozonolysis. It can therefore deteriorate and car tyres to crack.
14. What is the formula of ozone?
The formula of ozone is O3.
15. What is the formation of the ozone in the lower part of atmosphere?
In the lowest part of the atmosphere, ozoneacn 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 an electrical appliances; and by lightening. It can also be formed by passing a stream of oxygen through an electric discharge.
16. What is the formation of the ozone in the stratosphere?
In the stratosphere, ozone is formed from atmosphere oxygen by absorption of ultraviolet radiation of the right energy (wavelength250nm), which dissociates oxygen molecules into free oxygen atoms. The oxygen atoms produced then react with other oxygen molecules to from ozone.
17. What happen to ozone if it absorbs UV radiation of wavelength 215 to 295 nm?
If the ozone absorbs UV radiation of wavelength 215 to 295 nm, it undergoes
photodissoication and splits up again.
18. What is the significance of the above reaction?
The above 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?
Ozone is harmless in small concentrations. However, if the concentration rises above
100ppm, it will cause respiratory problems and headaches.
20. What would happen if the ozone layer becomes thinner?
Ozone layer can filter the dangerous ultraviolet radiation from the sun. If the ozone layer is too thin, it will cause an increase in the amount of ultraviolet light reaching the Earth 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?
Ultraviolet radiation, the free oxygen atoms and the CFCs would cause a decrease of
ozone in the atmosphere.
22. Using one of the substances in Q.21, write down the relevant equations for depletion of ozone in the atmosphere?
O3 (g)------O2(g)+O(g)
23. Give some alternatives for CFCs compounds.
Haloalkanes (which are not fully halogenated) and hydrocarbon such as butane and propaneare some alternative for CFCs compounds.
Water Pollution
- What are the causes of water pollution?
The causes are livestock waste, oil spillages, residues of pesticides, detergents in sewage and industrial effluents.
25. What are the effects of water pollution?
Livestock waste produces excessive amount of organic matter. When the organic matter discharged into water, the existing micro-organisms will grow and multiply rapidly. Oxygen is rapidly depleted. With the depletion of oxygen anaerobic bacteria begin to flourish. They break down the organic matter partially, releasing obnoxious and toxic gases like CH4, NH3 and H2S. As a result, aquatic organisms will die.
Oil from oil spillages floats on water. This blocks the oxygen supply to marine life and kills them. Oil also clogs the feather of sea birds and prevents them from flying or swimming. They then die of starvation. Oil interferes with insulation provided by the feathers, so the birds may die of cold or pneumonia. Birds trying to clean their feathers with their beaks may be poisoned through ingestion.
On entry into water, pesticides may either cause immediate toxic effects on aquatic life, or they may accumulate along the food chain until a toxic level is reached. DDT is an organo-chlorine pesticide widely used previously. The compound is fairly stable and can persist in the environment for a long time. Its fat solubility causes it to be concentrated in marine animals up the food chain, eventually accumulating in amounts that reach a toxic level to the animals. It can thus cause much ecological damage.
Detergents in sewage contain nitrogen or phosphorus which causes excessive plant growth and the population of primitive plants like algae explodes. This is called eutrophication. As a result of eutrophication, dense mats of rooted and floating plants are formed. Waterways become clogged, and boat propellers are fouled. The cost of removing the unwanted vegetation is enormous. Blue green algal blooms that appear on the water’s surface release unpleasant-smelling, bad tasting substances. The water becomes turbid, and unsuitable for swimming. The once attractive recreation areas are spoiled. As the vegetation and algae decay, they consume oxygen dissolved in the water; fish begins to die. If the concentration of dissolved oxygen continues to fall, other oxygen-dependent aquatic life will also be unable to survive.
Industrial effluents may be toxic, corrosive, flammable or give off explosive vapours. The wastes harm lives by bioaccumulation, the process by which a toxic substance becomes more concentrated as it moves upward through the food chain. The wastes which do not undergo treatment before dispose pose extreme hazards to workers handling the wastes, sewer workers, and passersby. The wasted will damage the sewerage and upset sewage treatment processes. The wastes end up in the sea polluting the marine environment and accumulating in sediments.
26. What does DO stand for?
DO stands for dissolved oxygen.
27. What is the indication of the DO value?
It indicates the oxygen content in water. It is measured in mg of oxygen per dm3 of water or percentage saturation of oxygen. High value indicates good water quality.
28. What does BOD stand for?
It stands for biochemical oxygen demand.
29. What does it mean by five-day BOD?
It is the BOD determined in the laboratory by incubating a sample of water for five days at 20oC and the amount of oxygen consumed measured.
30. What is the indication of the BOD value?
It indicates the amount of oxygen required to break down the organic matter present in a water sample, which is the extent of water pollution.
Solid Waste
31. What are the major causes of the solid waste?
They are the domestic households, commercial and manufacturing business and construction sites in the territory.
32. How we can dispose solid waste?
Landfilling and incineration are the two common methods.
33. What are the advantages and disadvantages of each type of disposal methods ofsolid waste?
The following are the advantages of incineration. The volume of the waste is reduced by approximately 55 per cent; the high temperature kills disease – causing organisms; there is no risk of ground water pollution; heat produced can be used as a source of energy and valuable metals like iron and aluminium can be recovered from the incinerator.
The disadvantages of incineration are more expensive and the toxic gases produced polluting the atmosphere. The large amount of carbon dioxide produced makes the problem of greenhouse effect worse.
The advantages of landfilling are that there is no bad smell and the high methane content landfill gas can be used as an energy source.
The disadvantages are that the filled lands are not suitable for building because the ground continues to settle for many years and money is needed to remove landfill gas and groundwater produced.
34. What are the pollution problems associated with the disposal of plastics?
Plastics contain plasticizers and CFC’s (chlorofluorocarbons). CFC’s damages the ozone layer which protects against harmful ultraviolet radiation that causes skin cancer and eye problems in humans and various disorders in animals. The plasticizers, such as PCB’s (polychlorinated biphenyls) can get leached out of a plastic and once in the environment. They can be incorporated into the food chain, eventually ended up in humans.
On land, plastic wastes contribute to unsightly litter scattered along roadways and in our parks and beaches. They provide breeding grounds for disease carrying insects and rodents. Not only are plastic discards found in all oceans of the world, but they man present as immediate danger to some fish. Small fish have been found dead with their digestive tracts clogged by fragments of plastic foam that they had ingested with their food. Sea animals have been suffocated to death by plastic bags.
One method to dispose plastics is landfilling. Plastics are synthetic polymers tailored for long life. They are water proof and resistant to the action of microorganisms so that they may take several hundred years to be broken down into water and carbon dioxide.
Another way to dispose of discard plastics is to burn the. However some plastics such as PVC contain such additives that will be converted into toxic gases during incineration. Combustion of plastic products such as PVC also produces hydrogen chloride, which can cause acid rain that damages the environment. Incinerators are corroded by acidic gases and clogged by those plastics that melt from the heat but do not burn. Although incinerators are equipped with electrostatic precipitator for the removal of particulates and dust from the flue gases, other gaseous emissions still present an air pollution problem to nearby residence.
35. How we can solve the pollution problems by solid waste?
For the problems of plastics, we can use degradable plastics. The general methods to solve the pollution problems by solid waste are the 3Rs: reduce, reuse and recycle. The government promotes this concept to increase public environmental awareness and participation in waste minimization and recycling activities. The 3Rs helps in saving resources, reducing the demand of valuable landfill space and reducing the polluting gases by incineration.
36. Which department in H.K. is responsible for the pollution control?
The Environment Protection Department (EDP) was established to control the pollution problem.
37.What are the measures to improve air quality? Describe each of them briefly with the help of equation(s).
- Use of unleaded petrol. During combustion, lead compounds react with other additives in petrol to form volatile lead halides which is toxic. Moreover, lead products can inactivate the catalysts in catalytic converters.
- Installation of catalytic converters in car exhaust systems. NO, CO and unburnt hydrocarbons present in car exhaust is the major source of air pollution. The converter contains precious metals, including rhodium and platinum as catalysts to catalyze these toxic gaseous to non-toxic one.
2NO(g) + 2CO(g) N2 (g) + 2CO(g) (oxidation)
2CO(g) + O2(g) 2 CO2 (g) (oxidation)
C7H16(g) +11O2 7CO2(g) + 8H2O(l) (oxidation)
- Limitaion of sulphur content in fuels.
To reduce the amount of sulphur dioxide in the air, diesel-driven vehicles are required to use diesel with sulphur content not more than 0.05% by weight, starting from 2000.
- Desulphurization of flue gas
To reduce the sulphur content in coal, a flue gas desulphurization (FGD) system can be used to remove up to 90% of sulphur emitted from a boiler plant.
SO2(g) +H2O(l) H2SO3(aq) (absorption)
The above reaction is reversible.
CaCO3(g) + H2SO3 (aq) CaSO3(s) + CO2(g) + H2O(l) (neutralization)
CaSO3(s) +1/2O2(g) CaSO4(s) (OXIDATION)
CaSO3(s) + 1/2H2O(l) CaSO3 ．1/2H2O(aq) (crystallization)
CaSO3(s) + 2H2O(l) CaSO4．2H2O(aq) (crystallization)
- Installation of electrostatic precipitators in power plants.
In electrostatic precipitation, flue gas from boiler is passed through a chamber where particulates being charged. The charged particles finally get attracted on the collecting wall. They are neutralized on the wall where they deposited and removed. The cleaned flue gas is then discharged through the chimney.
- Installation of low nitrogen oxides burners in power plants. The low nitrogen
oxides burner system utilizes a combustion control method in which the operating conditions for combustion are modified to reduce nitrogen oxides formation. These include a reduction in the flame temperation in the combustion zone and a reduction in the avaliability of O2 in Nox formation zone.