Group 2 Group member: Chan Tsz Mei Cheng Yu Sang Lai Tsz Ching Lam Wing Hon Tsui Yuk Ping South Tuen Mun Government Secondary School Chemistry Project Secondary 6 Chemistry and Society: Unit 46: Chemistry and the Environment 1. Define the terms pollution and pollutant. Ans: Pollution is the introduction of waste matter or energy into the environment by humans. It causes damages 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. 2. What are the major air pollutants? Ans: There are six major air pollutants. They are carbon monoxide, sulphur dioxide, nitrogen oxides, hydrocarbons, ozone and particulates. 3. What are their sources or formation with the help of equations? Ans: Carbon monoxide Carbon monoxide is the most common air pollutant in large cities. 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 may 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 operation in power stations and metal smelters in which sulphur-containing coal is used as the 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. In Hong Kong, the level of nitrogen oxides is noticeably high because of the high proportion of diesel-driven vehicles running in the territory. Diesel engines produce much less carbon monoxide but a lot more nitrogen oxides than petrol engines. Hydrocarbons Hydrocarbons 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 Ozone is produced by the reaction of oxygen gas with the 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 Particulates 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. They are solid or liquid particles and are so small that they remain suspended in air for a long period of time. 4. What are the common effects of these pollutants? Ans: Carbon monoxide Carbon monoxide is a poisonous gas. When one inhales it, it will enter the blood stream and bind preferentially to haemoglobin (the substance that carries oxygen) in red blood cells, thereby replacing oxygen. This result in the reduction of the amount of oxygen delivered to body organs and tissues. Carbon monoxide can cause death even in relatively low concentrations. The danger of carbon monoxides is heightened by the fact that the gas is colourless, tasteless and odourless. People may suffer from its effects before they are aware of its presence. Sulphur dioxide Sulphur dioxide is a colourless, toxic gas. It can cause impairment of the respiratory function, aggravation of existing respiratory diseases (especially bronchitis and asthma) and cardiovascular diseases. It is mostly the sulphur dioxide in air that causes acid rain. Acid rain can damage buildings and is also though to be responsible for the deaths of large numbers of trees in Europe and America. Nitrogen dioxide An example of nitrogen oxide is nitrogen dioxide which is reddish brown toxic gas with a very unpleasant pungent odour. It gives rise to photochemical smog. It can also irritate the lungs and lower our resistance to respiratory infections such as influenza. Individuals with respiratory problems, such as asthma, are more susceptible to the effects. In young children, nitrogen dioxide may also impair lung development. Nitrogen oxides also cause the formation of acid rain. Hydrocarbons Hydrocarbons cause photochemical smog. Certain hydrocarbons (e.g. benzene) are known carcinogens. Ozone Ozone has a great impact on the respiratory system. Symptoms associated with exposure to ozone include cough, chest pain, and throat and eye irritation. Ozone can also increase our susceptibility to respiratory infections and damage plants. Particulates The environment effects of particles depend on both the size and the nature of the particulates. Very fine particles (diameter less than about 1µm) are the most hazardous. 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. 5. 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, a well- know poisonous air pollutants, as an example. Of the concentration of carbon monoxide is 600-700 ppm, inhaling it for an hour brings about barely detectable effects. However, a concentration of 4000 ppm or higher can cause death in less than one hour. If an adult is exposed to an atmosphere containing 1000 ppm carbon monoxide for 4 hours, he is likely to die form carbon monoxide poisoning. 6. 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 (106) molecules in air. It is thus a ration with no unit. Based on the Avogadro’s law, ppm is also equal to the number of volumes of pollutants per million volumes of air. Parts per million (ppm) = Number of molecules of pollutants 106 molecules of air = Number of volumes of pollutants 106 volumes of air 7. Express 0.03 ppm SO2 as µgm-3. Ans: In 1 m3 of air, there is 0.03/106 sulphur dioxide. Using the ideal gas equation, PV = nRt = (Mass of SO2/M) RT where M is the molar mass of SO2. Mass of SO2 = PVM/RT = (101x103 Pa)(0.03/106 m3)(64.1 gmol-1) (8.314 JK-1mol-1)(298K) =79.9µg →The concentration of sulphur dioxide is 79.9µgm-3. 8. 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) 9. What are the two major air pollutants responsible for the formation of acid rain? Write down the relevant equations. Ans: Sulphur dioxide and nitrogen dioxide are the two major pollutants responsible for the formation of acid rain. Sulphur dioxide is mainly released from the burning of fossil fuels in power stations. In the atmosphere, sulphur dioxide is slowly oxidized to sulphur trioxide which dissolves readily in water droplets o form sulphuric(VI) aic. 2SO2 (g) +O2 (g) —> 2SO3 (g) SO3 (g) +H2O (l) —> H2SO4 (aq) The actual pathways are more complicated. The formation of sulphur trioxide from sulphur dioxide is influenced by the prevailing atmospheric conditions: sunlight, temperature, humidity and the presence of hydrocarbons, nitrogen oxides and particulates in the atmosphere. Sulphuric(VI) 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. 2H2SO3 (aq) + O2 (g)—> 2H2SO4 (aq) Nitrogen oxides released from the burning of fossil fuels in automobiles and power stations into the atmosphere also lead to the formation of acid rain. 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 nitric (V) acid. 4NO2 (g) + 2H2O (l) + O2 (g) —> 4HNO3 (aq) 10. 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 affected, resulting in the death of plants. Acid rain also corrodes metals and accelerates the rate of deterioration of buildings, rocks and statues. 11. 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, peroxyacrtyl nitrate (PAN) and unreacted hydrocarbons, etc. a brownish haze that irritates our eyes is an indicator of photochemical smog. Nitrogen dioxide is responsible for the brownish color of the haze. 12: how is the photochemical smog formed? Ans: Reactions that lead to the formation of photochemical smog are initiated by sunlight and involve hydrocarbons and nitrogen oxides emitted form automobiles. The combination of sunlight, particulate matters and abundant pollutants present in modern cities provide favourable conditions for smog formation. Nitrogen dioxide form automobile exhaust first absorbs sunlight and breaks down into nitrogen monoxide and free oxygen atom which is very reactive. UV light NO2 (g) —> NO (g) + O (g) 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 peroxyacrtyl nitrate (PAN). O ║ CH3─C─O─O─NO2 PAN molecule Very much simplified, some of the principal reactions involved in the formation of photochemical smog are illustrated below: O (g) + O2 (g) —> O3 (g) O (g) + hydrocarbons —> aldehydes O3 (g) + hydrocarbons —> aldehydes Hydrocarbons + O2 (g) + NO2 (g) —> lachrymatory substances, including 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. 13. 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. 14. What is the formula of zone? Ans: UV light O2 (g) —> 2O (g) O (g) + O2 (g) > O3 (g) 15. 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 atmosphere oxygen by absorption of ultraviolet radiation of the right energy (wavelength 250 nm), which dissociates oxygen molecules into free oxygen atoms. O2(g) → 2O(g) The oxygen atoms produced react with other oxygen molecules to form ozone. O(g) + O(g) → O3(g) 17. What happen to ozone if it absorbs UV radiation of λ 215 to 295 nm? Ans: When ozone absorbs UV radiation of λ 215 to 295 nm, it will undergoes photodissociation and splits up again. O3(g) → O2(g) + O.(g) 18. What is the significance of the above reactions? Ans: This reaction responsible for the vital screening effect of ozone. It screens off the harmful ultraviolet radiation. 19. What are the effects of ozone to human? Ans: Ozone has a great impact on the respiratory system. Symptoms associated with exposure to ozone include cough, chest pain, and throat and eye irritation. Ozone can also increase our susceptibility to respiratory infections. 20. What would happen if the ozone layer becomes thinner? Ans: The thinning of ozone layer may result in an increase in the amount of ultraviolet light reaching the Earth’s surface, leading to increase in the incidence of skin cancer, genetic mutation, and a decrease in the yield of crops. 21. What substances would cause a decrease of ozone in the atmosphere? Ans: CFCs 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: CCl3F(g) → CCl2F•(g) + Cl•(g) CCl2F2(g) → CClF2•(g) + Cl•(g) Cl•(g) + O3(g) → ClO•(g) + O2(g) ClO•(g) + O3(g) → Cl•(g) + 2O2(g) 23. Give some alternatives for CFCs compounds. Ans: Low ozone depletion potential, hydrocarbons such as butane and propane are possible alternatives for CFCs. Water Pollution: 24. What are the causes of water pollution? Ans: The adverse effects of each of the water pollution on the environment includes: Water pollution is 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: 1. Livestock waste When there is an excessive amount of organic matter discharged into water, the existing micro-organisms will grow and multiply rapidly and oxygen is rapidly depleted. Because of the lack of oxygen, anaerobic 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 Oil may clog the feathers of sea birds and prevent them from flying or swimming. It also interferes with the insulation provided by the feathers, so affected birds may die of cold or pneumonia. When birds try to clean their feathers with their beaks =, they may be poisoned through the ingestion of oil. Furthermore, oil floating on water prevents the dissolution of oxygen. Besides, oil deposited von beaches may drive away holiday-makers and spoils recreational resorts 3. Residues of pesticides Pesticides are synthetic organic compounds used to eliminate flying and crawling pests. On entry into water pathways, pesticides cause immediate toxic effects on the aquatic life. They are non-biodegradable and may accumulate along the food chain until a toxic level is reached. DDT is an organochlorine insecticide widely used previously. DDT has caused a lot of ecological damages because (a) It resists degradation and remains in the environment. (b) It is very soluble in fat, including the fat in milk and the body fat of the animals, with the potential for damaging internal organs. (c) It affects the reproduction of birds, fish, etc, and weakens the shells of eggs (d) Many species of insects can develop resistance to this insecticide. 4. Detergents in sewage Sewage is domestic waste water. A major pollutant present in sewage is synthetic detergent. Discharges of detergents causes eutrophication brought about 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 The toxic materials presents in the industrial effluents vary with the types of industries involved. They may contain heavy metals, cyanides, polychlorinated hydrocarbons, etc. Of particular concern in aquatic environments is the bioaccumulation of heavy metals. This is a process by which the heavy metals become more concentrated as they move up food chains. 26. What does DO stand for? Ans: DO stands for Dissolved Oxygen. 27. What is the indication of the DO value? Ans: If the level of dissolved oxygen falls below 5.0 mg dm³, fish start to die. If the concentration of dissolved oxygen continues to fall, other marine animals and aerobic bacteria will be unable to survive. In the complete absence of dissolved oxygen, decomposition of organic matter continues but it is taken over by non-oxygen requiring bacteria. The water begins to smell unpleasant as different pathways of decomposition are proceeding. 28. What does BOD stand for? Ans: BOD stands for Biochemical Oxygen Demand. 29. What does it mean by five-day BOD? Ans: Five-day BOD is BOD determined in the laboratory by incubating a water sample for five days at 20℃ and measuring the amount of oxygen consumed. 30. What is the indication of the BOD value? Ans: If the water has a high BOD, this implies that a lot of organic waste is present and much oxygen is required to break down the waste. On the other hand, a low BOD indicates the presence of only a small amount of organic matter and there is little organic pollution. Natural clean water has a BOD of about 1 to 4 mg dm³. If the BOD is greater than the amount of oxygen replenished, then some fish and aquatic life suffocate. Solid Waste: 31. What are the major causes of the solid waste? Ans: In Hong Kong, solid waste is produced as a result of the activities of domestic households, commercial operations, manufacturing industries, and construction sites in the territory. 32. How we can dispose solid waste? Ans: There are mainly two methods to dispose solid waste. They are by landfilling and incineration. For landflling, which is the major disposal method in Hong Kong, the waste is compressed and covered with soil at landfill sites. And incineration, it is more expensive than landfilling, and the solid waste are burnt off during incineration. 33. What are the advantages and disadvantages of each type of disposal methods of solid waste? Ans: Both landfilling and incineration have its advantages and disadvantages. For landfilling. Lnadfill gas, mostly methane, and leachate, which is highly polluting water percolating through decaying waste at landfill. The landfill gas contains chemicals which are flammable and harmful. For incineration, it is a more expensive method. However, the volume of waste can be reduced by approximately 55% and the high temperature kills disease-causing organisms. Moreover, it will not cause ground water pollution and the heat produced can be used as a source of energy. The disadvantages of it are due to its potential for polluting the atmosphere with toxic chemicals, particularly metals, and the large amount of carbon dioxide produced causes the grrenhouse effect on the globe. 34. What are the pollution problems associated with the disposal of plastics? Ans: As plastics are chemically tailored for long-life uses, they do not generally undergo decomposition at landfill sites and 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. Therefore, disposal of plastics by landfilling and incineration causes environmental problems. However, disposal of plastic waste directly in sea causes direct danger to fishes. Small fish have been found dead with their digestive tracts clogged by fragments of plastic foam ingested. Sea animals have been suffocated to death by plastic bags. 35. How we can solve the pollution problems by solid waste? Ans: We should use them lesser. And by 3Rs, we should also reuse, reduce and recycle. For the plastic, degradable plastics should be developed. These plastics included biopolymers, photodegradable plastics and synthetic biodegradable plastics. Plastics can also be recycle, which included direct recycling, recycling of energy and recycling of chemicals. In direct recycling, it can only apply to thermoplastics. The plastics in the waste are separated, cleaned, pulverized, and remoulded into new plastic items. In recycling of energy, incineration of plastics to produce energy is recycling f the energy content stored in the materials. The energy obtained from burning plastic waste in incinerators can be used for heating or for generating electricity. However, it may cause toxic gases, such as polychloroethene gives hydrogen chloride gas when burnt. The method of recycling of chemicals is by catalytic cracking. The large plastic molecules are broken down on the surface of a hot silica catalyst to smaller, more useful molecules. This process is known as pyrolysis, which is the thermal decomposition of a material at a high temperature and in the absence of air. The products are separated by fractional distillation and can be used to make plastics and other chemicals. Pollution Control in H.K.: 36. Which department in H.K. is responsible for the pollution control? Ans: The Environmental Protection Department, in short EPD established in 1986 is 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: The air quality can be proved by using unleaded petrol, installation of catalytic converters in car exhaust systems, limitation of sulphur content in fuels, desulphurization of flue gas, installation of electrostatic precipitators in power plants and installation of low nitrogen oxide burners in power plants. Firstly, during combustion of lead contained petrol, the lead compounds react with other additives in petrol to form volatile lead halides which pass out with the exhaust gases. Using unleaded petrol helps reducing these toxic lead compounds which causes anaemia, and damages the nervous system and the kidney. Moreover, infants are susceptible to lead poisoning. Secondly, installation of catalytic converters in car exhaust systems can reduce the content of nitrogen oxides, carbon monoxide and unburnt hydrocarbons present in car exhaust. The catalytic converter, the carbon monoxide is oxidized to carbon dioxide, unburnt hydrocarbons are oxidized to carbon dioxide and water, and nitrogen monoxide is reduced to nitrogen. The converter contains rhodium and platinum as catalysis. When car exhaust containing carbon monoxide, unburnt hydrocarbons and nitrogen oxides is passed through the converter, rhodium catalyzes the reduction of nitroden monoxide. Platinum catalyzes the oxidation of carbon monoxide and unburnt hydrocarbons such as heptane. 2NO(g) + 2CO(g) → N2(g) + 2CO2(g) 2CO(g) + O2(g) → 2CO2(g) C7H16 (g)+ 11O2(g) → 7CO2(g) + 8H2O(g) Thirdly, by limiting the sulphur content in fuels can reduce the sulphur dioxide emission from factories and power plants in which sulphur-containing fossil fuels are burnt. Fourthly, as sulphur dioxide is released during the combustion of coal which contains sulphur, using coal of low sulphur content, the quantity of sulphur dioxide released is much reduced. The desulphurization of flue gas utilizes the “wet limestone-gypsum scrubbing process” which is capable of removing up to 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 is directed to the absorber which contains a recycled slurry of limestone for removal of sulphur dioxide. The calcium sulphate(IV) formed is oxidized to calcium sulphate(VI) by the air blown into the bottom part of the absorber. The chemical reactions of the absorption and oxidation processes can be summarized as: SO2(g) + H2O(l) → H2SO3(g) Absorption CaCO3(s) + H2SO3(aq) → CaSO3(s) + CO2(g) +H2O(l) Neutralization CaSO3(s) +1/2 O2(g) → CaSO4(s) Oxidation CaSO3 + 1/2 H2O(l) → CaSO3‧ 1/2H2O(aq) Crystallization CaSO4(s) + 2H2O(l) → CaSO4‧ 2H2O(aq) Crystallization Fifthly, as coal contains a certain proportion of ash which cannot be burnt, installing electrostatic precipitators reduced the ash to clean the flue gas before its release into the atmosphere. In electrostatic precipitation, flue gas from the boiler is passed through a chamber where particulates become charged. The charged particles finally get attracted on the collecting wall. The charges on the particles are neutralized on the wall where they are deposited and removed. The cleaned flue gas is then discharged through the chimney. Finally installation of low nitrogen oxide burners in power plants lowering the content of nitrogen dioxide. Nitrogen oxides (NOx) usually include nitrogen monoxide and nitrogen dioxide by combustion. Nitrogen in the air reacts with oxygen at a high temperature near the combustion chamber to form nitrogen monoxide in a series of complex reactions: N2(g) + O2(g) → 2NO(g) When released into the atmosphere, it reacts with oxygen to form nitrogen dioxide. 2NO(g) + O2(g) → 2NO2(g) Another way to form nitrogen dioxide is that fossil fuels may contain nitrogen compounds. When these fuels are burnt, the nitrogen compounds are oxidized to nitrogen oxides, which are known as fuel nitrogen oxides. 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 temperature in the combustion zone and a reduction in the availability of oxygen in the nitrogen oxides formation zone. Reductions in the production of nitrogen oxides up to 50% have been demonstrated in these systems. 39. What does CWTC stand for? Ans: CWTC stands for Chemical Waste Treatment Centre. 40. What is the mission for the CWTC? Explain briefly. Ans: The mission for the CWTC is to provide proper waste treatment services for local waste producers. There are three major waste treatment systems in the Centre, ranging from oil/water separation system, physical/chemical treatment system and incineration. For oil/water separation system deals with oil/water mixtures. It recovers waste oil from oily water mixture and separation of water from all residue formed in neutralization and precipitation processes. The physical/chemical treatment system treats water-based chemical waste such as acids, alkalis, and wastewater containing heavy metal salts by neutralization of acids and bases, precipitation reactions and reduction reactions. Incineration system is used for destructing hazardous organic waste such as pesticides and cyanide waste by decomposing them to carbon dioxide, water and various gases. 41. What does it mean by 3Rs? Explain briefly. Ans: 3Rs refers to reduce, reuse and recycle. It is introduced by the HKSAR to arise the public environmental awareness and promote waste avoidance, minimization, recovery for reuse and recycling. For example, recycling bins for plastic bottles, aluminium cans and waste paper. For reducing, reusing or recycling of plastics, we have to reduce our uses of plastic bag after shopping in the supermarket. For the reusing and recycling of paper, we have to use the recycled paper produced by local recyclers is used to make corrugated paper and duplex papercard for packaging. Those computer printout waste papers, old corrugated cardboard, newspaper and other mixed paper, have to be collected for recycling. The metal articles such as furniture, kitchen ware and aluminium foils can by reused. Metal waste can be recycled by smelting used metals and using them again. For example, ferrous metal waste is processed in a local foundry to produce reinforcing bars for use in the construction industry. By recycling, reuse and reduce, not only the pollution problem of solid waste can be solved, it can also save fuels, energy, and other chemicals in the solid. Chemistry and Society : Unit 47 : Chemistry and Food: 1. What is the product formed when protein undergoes hygrolysis? Ans: constituent amino acid 2. What are the classification of carbohydrates? Ans: monosaccharide, disaccharide, polysaccharide 3. What is the general formula for carbohydrates? Ans: (C6H10O5)n 4. What does it mean by the acyclic and cyclic forms of glucose molecule?What does it mean by glycosidic linkage in carbohydrates? Ans: The acyclic form of glucose molecule is an aldohexane as it contains an aldehyde group in its acyclic structure. The cyclic forms of glucose are dissolved in water, either of them will be converted to the other form, until an equilibrium mixture is formed, together with a minute amount of the acyclic form. 5. Illustrate by an example. Ans: the bond formed between two monosaccharide is called a glycosidic linkage. It is formed from the condensation reaction between two –OH groups of two monosaccharides with the elimination of a H2O molecule. For example, a maltose molecule is built up from two-glucose molecules with the elimination of a H2O molecule. 6. What is/are the factor(s) affect the hydrolysis of sucrose and starch? Ans: Sucrose: hydrolyzed by dilute mineral acids or catalyzed by maltase Starch: catalyzed by enzymes (amylase) or boiled with dilute sulphuric(VI) acid. 7. What are the basic structural units for the fat? Ans: H O ∣ ‖ H—C—O—C—R1 O ∣ ‖ H—C—O—C—R2 O ∣ ‖ H—C—O—C—R3 ∣ H 8. Write down a general equations for the formation of soap by using natural fat. Ans: H O ∣ ‖ H—C—O—C—R1 O ∣ ‖ H—C—O—C—R2 ∣ O ‖ H—C—O—C—R3 ∣ H + 3NaOH H ∣ H—C—OH ∣ + H—C—OH ∣ H—C—OH ∣ H O ‖ R1—C—O-Na+ O ‖ R2—C—O-Na+ O ‖ R3—C—O-Na+ 9. Define the term “iodine value”? Ans: Its determination is based on the reaction between iodine and the C=C bonds in fats or oils. The iodine value of a fat or an oil is defined as the number grams of iodine that reacts with 100 grams of the fat or oil. 10. What is the indication of the iodine value? Ans: The higher the iodine value, the greater is the degree of unsaturation in the fat or oil. 11. What does it by hardening of vegetable oil? Ans: The C=C double bonds in these unsaturated oils may be converted to single bonds by the addition of hydrogen in the presence of a catalyst. The process is called hydrogenation. Hydrogenation of some of the carbon-carbon double bonds in these bonds in these oils thus converts them into solid fats. 12. What does it mean by rancidity? How many types are there? Describe each of them with the help of equations. Ans: Fats and oils are liable to spoilage which results in the production of an ‘off’ odour and a flavour described as rancidity. It is mainly caused by hydrolytic or oxidative reactions which release foul smelling aldehydes and fatty acids. Hydrolytic rancidity is due to the presence of moisture in fats and oils, which causes the hydrolysis of the glyceride molecules to propane-1,2,3 triol and free carboxylic acids. Food Preservation: 13. What are the causes of food spoilage? Ans: Food spoilage is due to the activities of micro-organisms (bacteria, moulds and yeasts) and, to a lesser extent, chemical reactions which are often catalyzed by enzymes. 14. Give some principle of food preservation. Ans: The food preservation is commonly by slowed down the deterioration in quality, and to increase the food’s shelf-life. The principle is that microbial or chemical changes resulting in food spoilage are suppressed, such as removal of moisture inside food, altering temperature, changing pH, use of osmotic process and use of chemical additives. Both removal of moisture and use of osmotic process are useful as their principle is by removing the water inside food since the presence of water is one of the necessary conditions for microbial growth in food. Using altering temperature is by killing the bacteria and micro-organisms under high temperature or by retarding the growth of micro-organisms under low temperature. As most micro-organisms prefer a neutral or slightly acidic medium for growth. Increasing or decreasing the pH value creates an unfavorable condition for their growth. Finally, adding chemicals can inhibit or slow down microbial activities in food. 15. Give some common techniques of food preservation. Briefly describe the principle behind each of them. Ans: There are several methods in preserving foods. The most common techniques of them involve the killing of micro-organisms, inhibition of microbial growth, or the retardation of chemical changes. Some common techniques of food preservation used include heat treatment, drying and dehydration, irradiation, refrigeration, sugaring, salting, canning and some chemical techniques. The heat treatment kills micro-organisms, alters protein structures, and destroys enzymatic activities of micro-organisms in food during the process. All forms of cooked food are preserved by this method. Another method is by irradiation. During this process, food to be preserved can be exposed to ionizing radiation. The radiation destroys enzymes and micro-organisms in food. It is very common in preserving fruits. The drying and dehydration is the oldest practice of food preservation. Water is extracted and the absent of water makes chemical reactions cannot occur and micro-organisms cannot grow. The refrigeration method involves chilling and freezing. The chilling slows down microbial and enzymatic activities, as well as chemical and biochemical changes, so food spoilage can be avoided. And in freezing, the temperature of food is reduced to about -18C oC. Freezing turns the water present in the food to ice and no water is provided anymore. Moreover, sugaring and salting both treated the food with concentrated solution in order to remove the water in food by osmosis to the concentrated solution. Hence, as no water is available longer for enzymatic action and microbial growth. In canning, food is cooked under pressure in hermetically sealed containers. Cooking destroys enzymes and micro-organisms in food. As the cans are sealed, there is no air and no micro-organisms can get in. Meat-curing is done by adding salt to meat or treating the meat with concentrated salt solutions containing nitrates(V) and nitrates(III). The salt ties up the water in food so that micro-organisms cannot multiply and grow, and chemicals such as nitrates (III) prohibit their growth. Picking in vinegar can be another effective method as microbial growth is inhibited in acidic solutions. Finally, use of food additives can control the growth of micro-organisms and chemical spoilage are added to food. The added substances inactivate or kill micro-organisms, retard chemical spoilage, but the considered relatively safe to humans. 16. What are the functions of BHA / BHT? Ans: The butylated hydroxyanisole, in short BHA and butylated hydroxytoluene (BHT) are antioxidant used in food to retard the development of oxidative rancidity in unsaturated fats and oils. They appear to work by donating the H atom of the ─OH group to the free hydroperoxide radical (ROO ●) involved in the autoxidation of fat and oils, thereby stopping the chain reactions in oxidative spoilage: AH + ROO ● → ROOH + A ● where AH represents the antioxidant, and A ● is a radical derived from the antioxidant. These antioxidants are added to vegetable oils, shortening and products that contain unsaturated oils and fats. 17. What are the possible menace of using too much food additives? Ans: Too much food additives cause allergies, hyperactivity and other long-term illnesses. Some people are allergic to certain additives. It is suspected that MSG and tartrazine may cause rashes, stomach upsets and asthma. And food additives was suggested to the diseases hyperactivity and attention deficient disease (ADD) in children. Some other additives, such as sodium nitrate (III), are suspected to be carcinogens. Some additives are believed to be the causes of some long-term illnesses. Small amount of them can prevent cancer, however, larger amounts of it can cause cancer. When sulphur dioxide is poisonous and when it is ingested, sulphur dioxide salts attack the respiratory system if it is used as food additive. 18. What is the use of the monosodium glutamate (MGS) in food processing? Ans: Monosodium glutamate (MGS) does not add any taste to food but it is a flavour enhancer. It is the monosodium salt of glutamic acid which is an amino acid. It is found naturally in many fresh meats and vegetables such as mushrooms, peas and tomatoes. It enhances the flavour of food and makes the food taste better. One explanation of how MSG works is that MSG stimulates glutamate receptors in the tongue and thus enhances meat-like flavours. Another explanation is that MSG increases the sensitivity of our taste buds and stimulates the flow of saliva, which starts the breakdown of food, thus releasing its flavour. 19. What are the side effects of MSG? Ans: MSG may cause some possible symptoms and side effects. These include burning sensation, thirst, headache, chest pain, vomiting and abdominal discomfort. The side effects are more prominent in some individuals than others and are dose-related. 20. What is the use of nitrate (Ⅲ)/ nitrites or nitrate (Ⅴ) in food processing? Ans: Nitrates (Ⅲ) and nitrates (Ⅴ) are often used as preservatives in many cured and canned meats. In the meats, nitrates(Ⅴ) are reduced to nitrates(Ⅲ). The nitrates (Ⅲ) are actually responsible for developing the cured aroma and fresh pink colour in meats and they are also for inhibiting bacterial growth. Nitrates (Ⅲ) are particularly effective in preventing botulism. 21. What are the side effects of nitate(Ⅲ)/ nitrites of nitrate(Ⅴ)? Ans: Excessive ingestion of nitrates (Ⅲ) causes decreased levels of haemoglobin in the blood. Long-term ingestion may even lead to malnutrition, growth retardation, impairment of reproductive capacity and reduced lifespan. Nitrates(Ⅴ) are fairly harmless, but dietary nitrates(Ⅴ) ingested from vegetables and meats are also reduced to toxic nitrates(Ⅲ) in our body. Nitrates(Ⅲ) in the body may give rise to the formation of some carcinogenic nitrosamines. In the stomach nitrates(Ⅲ) are first converted to nitric(Ⅴ) acid. NaNO2 (aq) + HCl (aq) → HNO2 (aq) + NaCl (aq) Stomach juice Then, nitric(Ⅲ) acid can react with secondary amines, which are released during digestion of proteins, to form carcinogenic nitrosamines under certain conditions. HNO2 (aq) + R2NH (aq) → R2N-N=O (aq) + H2O (l) Secondary amine nitrosamine 22. What is the use of SO2 in fruit juice? Ans: The food additives, sulphur dioxide, is a collective term for sulphur dioxide gas and its salts, namely sulphates (Ⅳ), hyhdrogen-sulphates(Ⅳ) and disulphates(Ⅳ). Both sulphur dioxide and sulphates(Ⅳ) help maintain the colour and the vitamin C of the fruit juice. They are used as bleaches and antioxidants to prevent browning in fruit juices and also other foods, such as alcoholic beverages, dried fruits and vegetables. 23. What are the side effects of SO2 in fruit juice? Ans: SO2 is poisonous. When sulphur dioxide and its salts are ingested, they attack the respiratory system. Individuals who suffer from chronic respiratory diseases such as bronchitis of asthma are much more susceptible to the attack. Therefore, the daily intake of SO2for humans should not exceed 0.7 mg per kg body weight. 24. What is the use of saccharin? Ans: Saccharin is an organic compound about 500 times sweeter than ordinary sugar. Although it has no food value, it is used as a sweetener due to its intense sweetness. It is used as a sugar substitute and diet sugar, especially for patients of diabetes, since it has a low calorific value. 25. What are side effects of saccharin? Ans: According to some studies, high doses of saccharin in second generation rats are linked to bladder cancer. Consequently, saccharin has been banned as and additive in Canada and it is allowed to be sold in pharmacies as a table-top sweetener only. Nevertheless, whether or not saccharin is carcinogenic in humans is still an open question. 26. What is the use of E number in food additive? Ans: E number is a coding system that is used on food manufactured in European Union (Eu) countries. The letter E tells us that the addictive is approved by Eu and the first digit tells us what class of additive it is. The following table shows the E numbers of some food additives. Type of additive E number Colourings Most begin with 1 Preservatives Most begin with 2 Flavourings Not numbered Antioxidants E300-321 Emulsifiers and stabilizers E322 and some numbers between E400 and E495 Acids, bases and buffers Most begin with 5 Sweeteners Most begin with 4 or 6 27. Are food additives being used extensively, and why? Ans: Yes, food additives are being used extensively due to their uses. They are present in food as a result of any aspect of production, processing, treatment, packaging, transportation or storage. Most additives are added intentionally so that food can last longer and the original characteristics of the food are retained. This plays a key role in maintaining high qualities and constancy of characteristics demanded by consumers nowadays. 28. To what extent do food additives threaten our health and general well-being? Ans: Food additives threaten our health and general well-being to certain extant. Although food additives seem to be a necessary part of the modern society, it cannot be denied that there are hazards associated with their uses. One of the possible harmful effects of food additives to our health is allergies. Some people are allergic to certain additives and it is suspected that MSG and tartrazine may cause rashes, asthma and stomach upsets. Moreover, it was suggested by some scientists in the 1970s that food additives may be related to hyperactivity and attention deficient disease (ADD) in children. Furthermore, some additives, such as sodium nitrate(Ⅲ), are suspected to be the causes of some ling-term illnesses. 29. Are there effective solutions to these problems? Ans: Yes, there are some solutions to these problems. The use of food additives can be monitored by research and legislation. Also, we should not take more than the maximum amount of individual additives which are suspected to be harmful suggested by scientists. As a result, our health and general well-being will not be threatened by the food additives. 30. What is being done to tackle these problems? Ans: The use of food additives is monitoring by research and legislation to tackle the problems. Substances, such as salt, sugar, vitamins and some minerals, which have long been used as additives to food, are generally recognized by experts as safe to use, based on their extensive history or on published scientific evidence. Apart form them, no food additive may be used unless it has been granted approval. Studies using animals to show the effects caused by the intake of certain food additives are often carried out at expected levels of human consumption. The data obtained are then compiled and lists of permitted additives are published. In the mean time, scientists are continuing to study the potent effects of the additives on humans, while watching out for any adverse ones. Moreover, the use of food additives is governed by legislation in many countries. In the USA, the Food and Drug Administration is responsible for monitoring the safety, purity, and wholesomeness of food and food additives. In the United Kingdom, the Food Advisory Committee compiles lists of food additives permitted by the government. For countries in the European Union (Eu), a permitted food additive is assigned a E number. In Hong Kong, the department of Health is responsible for the monitoring and legislation of food additives. The department is empowered under the Public Health and Municipal Services Ordinance to: (i) legislate permissible additives and maximum limits of additives in particular food; (ii) require supply of information on the composition of substances used in the preparation of food; (iii) check food labelling; (iv) inspect food-processing industries; (v) take samples of foods and food additives for chemical analysis; (vi) seize and destroy food; (vii) prosecute for false labeling or advertisement, using non-permitted additives or using additives beyond the permissible limits. 31. Can we, or can we not, do away completely with food additives? Ans: No, we cannot do away completely with food additives. If food additives are not used, much of our food will spoil and many people will die of starvation. Besides, diseases due to vitamin and mineral deficiencies may flourish. Food additives seem to be a necessary part of the modern society. 32. Should all food additives be banned by legislation? Ans: No, not all food additives should be banned by legislation, but only the toxic and harmful food additives should be banned by legislation. It is because food additives are useful and they play an important role in our daily life. They have been used for centuries in preserving and improving the appearance and colour of food. For example, salt, sugar and vinegar are used to preserve meat, fruits and vegetables respectively; herbs and spices are added to improve the flavour of food. Moreover, food additives are widely used in the food processing industry. They play a vital role in reducing diseases due to deficiency in nutrients. Besides, additives help assure the availability of wholesome, appetizing and affordable foods that meet consumer demands from season to season.