Chemistry ProjectGroup 4Group 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 Environment1. 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.

2. What are the major air pollutants?Ans: The major air pollutants are carbon monoxide, sulphur dioxide, nitrogen oxides, hydrocarbons, ozone, and particulate.

3. 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 burntNitrogen 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 radicalParticulates: 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.4. 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.

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 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.

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 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.

7. Express 0.03 ppm SO2 as μg m per cube.Ans: 85.437 μg m per cube.

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: 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)

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 affects, 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, peroxyacetyl nitrate (PAN) and unreacted hydrocarbons, etc.

12.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.

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. 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.

14.What is the formula of ozone?Ans: O3

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 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 ofthe 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 CH3CHF2 are 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-3 of 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 converter I 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 Slaked lime, Ca(OH)2, is commonly used to neutralize acid waste, while sulphuric(VI) acid is

used to neutralize alkaline waste.

H+(aq)+OH-(aq)---H2O(l) Precipitation reaction An alkali is used in removing metals from a number of metal-containing wastes. For

example, iron can be removed from the spent iron(III) chloride etchant by precipitation.

Fe3+(aq)+3OH-(aq) --Fe(OH)3(s) Waste solution of zinc, copper and nickel are treated similarly to remove the metals. Spent

ammonium chloride and copper(II) chloride etchants are treated with caustic soda, NaOH, to recover copper(II) oxide which is a marketable product.

NH4+(aq)+OH-(aq)---NH3(aq)+H2O(l)

Cu2+(aq)+2OH-(aq)---Cu(OH)2(s)

Cu(OH)2(s)---CuO(s)+H2O(g) Ammonia produced in the waste etchant treatment process is treated with sulphuric(VI)

acid to form ammonium sulphate(VI) which is also a marketable product.

2NH3(aq)+H2SO4(aq)---(NH4)2SO4(aq) Reduction reaction Soluble chromium(VI) compounds are usually found in the effluent of metal-finishing plants.

It is first reduced to a non-toxic chromium (III) compound and then precipitated as hydroxide. The reducing agents commonly used are sodium sulphate(IV), sulphur dioxide and iron(II) sulphate(VI). The following equations show one of such processes:

2H2CrO4(aq)+3Na2SO3(aq)+3H2SO4(aq)---

Cr2(SO4)3(aq)+3Na2SO4(aq)+5H2O(l)

Cr2(SO4)3(aq)+6NaOH(aq)---2Cr(OH)3(s)+3Na2SO4(aq)

39. What does CWTV stand for?Ans: CWTC stands for Chemical Waste Treatment Centre.

40. What is the mission for the CWTC? Explain briefly.Ans: CWTC is to provide proper waste treatment services for local waste producers. There are

three major waste treatment systems in the Centre: 1. Oil/Water separation system

It recovers waste oil from oily water mixture.2. Physical-chemical treatment system

It treats water-based chemical waste such as acids, alkalis, and wastewater containing heavy metal salts.

3. High temperature chemical waste incineratorIt destroys hazardous organic waste such as pesticides and polychlorinated biphenyls and cyanide waste.

41. What does it mean by 3Rs? Explain briefly.Ans: 3Rs means ‘Reduce, Reuse, Reduce’. It helps in minimizing waste, reducing the demand for scarce landfill space and saving resources. Discarded items such as newspaper, office paper, aluminium cans, glass containers and certain plastic items can be collected for reusing or recycling.

Unit 47: Chemistry and Food

1. What is the product formed when protein undergoes hydrolysis?Ans: the products formed are its constituent amino acids as shown below:

to the top, it is the equation we consider.

2. What are the classification of carbohydrates?Ans: carbohydrates are classified as follow:1: monosaccharideseg: glucose, galactose, fructose2: disaccharides:eg: maltose, lactose, sucrose3: polysaccharides: eg: starch, cellulose, glycogen*starch contains both amylopectin and amylose

3. What is the general formula for carbohydrates?Ans: Cx(H2O)y where H:O must be 2:1

4. What does it mean by the acyclic and cyclic forms of glucose molecule?Ans: acyclic is a kind of open structure shown below (fig1). Normally, it doesn’t exist in solid state of carbohydrates, but in cyclic form shown in (fig2)

5. What does it mean by glycosidic linkage in carbohydrates?Ans: The bond formed by two monosaccharides is called glycosidic linkage.

Illustrate by an exampleAns: two glucose molecules link together as shown above.

6. What is/are the factor(s) affect the hydrolysis of sucrose and starch?Ans: the presence of dilute mineral acids for the hydrolysis of sucrose:C12H22O11+H2OC6H12O6+C6H12O6Sucrose fructose glucose

The hydrolysis of starch is in the presence of amylase:2(C6H10O5)n+nH2OnC12H22O11starch maltose

7. What are the basic structural units for the fat?Ans: triglycerides, phospholipids, steroids are examples:

Write down a general equations for the formation of soap by using natural fat.

8. Define the term ‘iodine value’Ans: iodine value refers to the reaction between iodine(the more reactive iodine monochloride is used) and the CC double bonds in fats or oils. The purpose of this reaction is to measure the degree of unsaturation of fats or oils. The higher the degree of unsaturation of a fat or an oil, the greater amount of iodine it will react with.

9. What is the indication of the iodine value?Ans: iodine value of a fat or an oil is defined as the no. of grams of iodine that reacts with 100grams of the fat or oil. The higher the iodine value, the greater is the degree of unsaturation in the fat or oil.

10. What does it mean by hardening of vegetable oil?Ans: vegetable oils contain glycerides of unsaturated carboxylic acids. They usually exist as a liquid at room temperature of account of their low melting point. By hardening them, the CC double bonds in these unsaturated oils may be converted to single bonds by adding hydrogen in the presence of catalyst to make the oils exist in solids at room temperature. The process is called hydrogenation. 12. What does it mean by rancidity? How many types are there? Describe each of them with the help of equations.Ans: rancidity means if the oils of fats are kept for too long, they will release foul smelling aldehydes and fatty acids.There are two types of rancedity, they are:Hydrolytic rancidity:It is due to the presence of moisture in fats and oils, which causes the hydrolysis of the glyceride molecules to propan-1,2,3-triol and free carboxylic acids. The reaction is speeded up in the presence of certain microorganisms or in the presence of some enzymes.Eg: frying of potato chips in oil at high temperature. The water released from the chips causes the hydrolysis of oil. The liberated carboxylic acids may be volatile and have extremely unpleasant odours and flavours.

The equation is shown below:

Oxidative rancidity:It occurs when fats or oils are exposed to air and undergo oxidation. It results in the production of flavours such as ‘tallowy’.Fats and oils with a high degree of unsaturation easily be oxidized.The process of oxidation is a free radical mechanism and is speeded up by trace metals, light and free radical initiators. The reaction of a segment of an unsaturated carboxylic acid chain is shown below:

the hydroperoxides produced are flavourless and odourless, but can easily decompose o form highly reactive hydroperoxide free radicals.These radicals set up a chain reaction and produce volatile, flavoured compounds of aldehydes, ketones and carboxylic acids, which are responsible for their rancid flavour. The process is called autoxidation.Hydroperoxidehyperoxide free radical(cleavage of double bonds) aldehydes, ketones and carboxylic acids.Autoxidation can be controlled, but can’t be eliminated.

13. What are the causes of food spoilage? Ans: Food spoilage can be due to microbial activities and chemical changes.Fungi, yeasts and bacteria are the main microorganisms attack the food.

14. Give some principle of food preservation.

Ans:1: removal of moisture:-suppress chemical and biochemical changes of the food-kill the microorganisms.Eg: drying and dehydration are examples.2: changing pH: increase or decrease the pH values of food creates an unflavourable condition for the growth of microorganisms.(they live at a pH ranging from 4.5-10)eg: vinegar in pickling.3: uses of osmotic process: -water is important for the survival of microorganisms.-putting food in concentrated salt or sugar solution can led the microorganisms losing water by osmosis.-suffered from dehydration.

15. Give some common techniques of food preservation. Briefly describe the principle behind each of them.Ans:heat treatment:heat kills microorganisms, alters protein structures of the microorganisms to destroy their enzymatic activities in food.Eg: the sterilization of milk by UHTirradiation:food can be exposed to ionizing radiationthe radiation destroys enzymes and microorganisms in food.canning:food can be cooked under pressure in hermetically sealed containers.Cooking first destroys enzymes and microorganisms in food.The cans are sealed so that no air and no microorganisms can get in.

16. What are the functions of BHA / BHT ?Ans: BHA (butylayed hydroxyanisole) and BTH (butylated hydroxytoluene) are used as antioxidants 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 fats 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.

They are added to vegetable oils, shortening and products that contain unsaturated oils and fats, such as breakfast cereals, potato crisps, cheez balls, bread and sausages.

17. What are the possible menace of using too much food additives ?Ans: (a) allergies

- certain people may develop rashes, stomach upsets, ect. With particular additives;(b) hyperactivity- some additives, particularly colorings, are believed to cause hyperactivity in children.

Hyperactive children are those who are over-active and do not sleep much;(c) long-term illness- some additives have been banned because they cause long-term illness, such as

cancer.

18. What is the use of the monosodium glutamate (MSG) in food processing ?Ans: Monosodium glutamate (MSG) is used widely as a flavour enhancer. It works by increasing the sensitivity of the taste buds, or perhaps by stimulating saliva flow, which begins the breakdown of food to release the flavour. That means, it does not change the original flavour of the food but make it much more noticeable and tasty. It is commonly used in chicken broth, oyster sauce, soup bases for instant noodles and dim sums.

19. What are the side effects of MSG ?Ans: Side effects of “MSG Syndrome” include burning sensation, thirst, headache, chest pain, vomiting and abdominal discomfort. When ingested in large amount, it may also cause brain damage.

20. What is the use of nitrates (III) / nitrites or nitrates (V) in food processing ?Ans: Nitrates (III)/nitrites and nitrates (V) are often used together as preservatives in many cured and canned meats. Nitrates (III)/nitrites and nitrates (V) of sodium and potassium can slow down microbial growth, maintain the pink colour of meat and prevent botulism in canned foods.In meat, nitrates (V) are reduced to nitrates (III). It is actually the nitrates (III) which are responsible for the developing the cured aroma and fresh pink colour in meats, and for inhibiting bacterial growth. Nitrates (III) are particularly effective in preventing botulism

21. What is the side effects of nitrates (III) / nitrites or nitrates (V) ?Ans: Excessive ingestion of nitrates (III) causes decreased levels of haemoglobin in the blood. Long-term ingestion may lead to malnutrition, growth retardation, impairment of reproductive capacity and reduced lifespan. Nitrates (V) themselves are fairly harmless, but dietary nitrates (V) ingested from meats and vegetables are also reduced to toxic nitrates (III) in our

body.It is chemically possible that 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 (III) acid. For example,NaNO2(aq) + HCl(aq) → HNO2(aq) + NaCl(aq) in stomach juice

Under certain conditions, nitric (III) acid can react with secondary amines, which are released during digestion of proteins, to form nitrosamines.HNO2(aq) + R2NH(aq) → R2N―N═O(aq) + H2O(l) secondary amine nitrosamines

Cooking of cured meats at high temperature (especially frying of bacon) can lead to the formation of nitrosamines. Many forms of nitrosamines have been established to cause cancer.

22. What is the use of SO2 in fruit juice ?Ans: Sulphur dioxide is used as bleach and antioxidant to prevent browning in fruit juice.

23. What are the side effects of SO2 in fruit juice ?Ans: Sulphur dioxide is poisonous. When indigested, sulphur dioxide and its salts attack the respiratory system. Individuals who suffer from chronic respiratory diseases such as bronchitis or asthma are much more susceptible to attack.

24. What is the use of saccharin ?Ans: Saccharin is a kind of sweetener about 500 times sweeter than ordinary sugar (sucrose). It has low calorific value and is therefore used as a sugar substitute or diet sugar. It is also used in the production of sugar-free foods for patients of diabetes and diet soft drinks.

25. What are side effects of saccharin ?Ans: Laboratory studies have demonstrated that high doses of saccharin cause cancer in mice. Its carcinogenic potency in humans is still under investigation.

26. What is the use of E number in food additive ?Ans: All packaged foods and drinks in the European Union (EU) are required to display a full list of additives, either by name or E number, The E number is a coding system that is used on food manufactured in EU countries, The letter E tells us that the additive is approved by EU. The first digit tells us what class of additive it is.

27. Are food additives being used extensively, and why ?Ans: Yes, food additives are being used extensively. It is because food additives are widely

used in the food processing industry. They play an important role in reducing diseases due to deficiency in nutrients. Besides, additives are used to maintain palatability and wholesomeness. They are also used in preserving and improving the appearance and colour of food. Moreover, they are used to maintain product consistency, provide leavening or control acidity and alkalinity and also improve or maintain nutritional value.

28. To what extent do food additives threaten our health and general well- being ?Ans: Food additives have potent effect on humans, they affect growth, reproduction, the structure of various organs, the prevalence of cancer, or may accumulate in the body. Therefore they cause some serious diseases depending on the amount of additives ingested. These effects may also be brought to our offspring and make the use of additives more dangerous.

29. Are there effective solutions to these problems ?Ans: Yes, there are some effective solutions for examples, we can eat more fresh food instead of processed food and government can educate the people to eat less processed food. Moreover, government can also promote the side effects of ingesting large amount of food additives such that people will eat less processed food.

30. What is being done to tackle these problems ?Ans: 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: 1. legislate permissible additives and maximum limits of additives in particular food;2. require supply of information on the composition of substances used in the preparation of

food;3. check food labelling;4. inspect food-processing industries;5. take samples of foods and food additives for chemical analysis;6. seize and destroy food;7. prosecute for false labelling or advertisement, using non-permitted additives or using

additives beyond the permissible limits.All these can limit the used of food additives and prevent the excessive use of food additives in order to protect our health.

31. Can we, or can we not, do away completely with food additives ?Ans: My answer is definitely no. Food additives include:1. preservatives

2. antioxidants3. emulsifiers4. flavour enhancer5. flavouring 6. colouring agents7. nutrientsWe may do away with 4 to 7 as these additives are only used to make the food more attractive. However 1- 3 are used to keep the food in a good condition, in order that we would not be sick when eating that food. For example, the principle of using of preservatives is to prevent microbial growth and spoilage in food. Nowadays, chemical preservatives are widely used and commonly adopted in the food industry. Some food like fruit juices, dried vegetable, canned food and most the food we buy in the supermarket are added with preservatives. Keeping food for a long time, we cannot but to add preservatives, antioxidants, and emulsifiers. Moreover, most of the food are added with food additives nowadays, it is another reason why we cannot get rid of them.

32. Should all food additives be banned by legislation ?Ans: All the food additives should not be banned by legislation. Since some food additives are useful for example they act as food preservatives to control the growth of micro-organisms and chemical spoilage are added to food. Moreover some of them also act as emulsifiers. Emulsifiers are substances that keep very small droplets of a non-polar liquid (usually oil) evenly dispersed in a polar liquid (usually water). Therefore without emulsifiers, oil droplets cannot be kept in water. Then dairy products like ice-cream, mayonnaise, margarine and peanut butter cannot be produced.Actually, if food additives are used in limited, then the bad effects that they bring can be control. Therefore only the additives that others can replace their functions should be banned. Otherwise those are necessary to us should be kept.