21st Century Chemistry Structured Question in Topic 7 Fossil Fuels and Carbon Compounds Unit 25-29

Transcription

1 21 st entury hemistry Structured Question in Topic 7 Fossil Fuels and arbon ompounds Unit The following diagram shows a simplified structure of a fractionating tower in petroleum refinery. (a) ow was petroleum formed in nature? Petroleum was formed from dead remains of marine plants and animals that lived millions of years ago under high temperature, high pressure and action of bacteria. (b) (i) Name the process that takes place in the fractionating tower. Fractional distillation of petroleum (ii) Does the process involve physical or chemical change? Explain your answer. It involves physical change. It is because no new substance is formed in the process. (c) (i) Explain, in terms of molecular size, why fraction A has a lower boiling point than fraction D. The molecules in fraction A are smaller than those in fraction D, hence the van der Waals forces between the molecules in fraction A are weaker. (ii) State two other differences between the properties of fraction A and those of fraction D. Any two of the following: viscosity / flammability / colour / sootiness of flame / ease of evaporation [1 x 2] (d) (i) Suggest what fraction A may be. A: refinery gas (ii) Fractions B and are used as fuel for jets and lorries respectively. Suggest what fractions B and may be. B: kerosene : diesel oil (iii) Fraction D is bitumen. Suggest one use of bitumen. It is used in road surfacing.

2 (e) Draw a labelled diagram to show how the above process can be taken place in the laboratory. [3] (16 marks)

3 2. rude oil is often considered as a fossil fuel. The following experimental set-up is used to separate a sample of crude oil into different fractions. (a) Why is crude oil considered as a fossil fuel? rude oil originates from dead remains of marine plants and animals that lived millions of years ago. (b) (i) Name the process shown in the above diagram. Fractional distillation (ii) Why can crude oil be separated into different fractions by this process? It is because the components in the crude oil have different boiling points. (c) (i) What is the function of cold water in the experimental set-up? To condense the vapour given off into liquid. (ii) Why should the thermometer be placed exactly next to the opening of the delivery tube? To ensure the temperature measured is exactly the boiling point of the vapour leaving the boiling tube. (d) Two fractions, A and B, are collected at 100 and 250 respectively. State how these two fractions are different in (i) sootiness of flame; Fraction A burns with a less sooty flame than fraction B. (ii) viscosity; and Fraction A is less viscous than fraction B. (iii) molecular size. Molecules in fraction A are smaller than molecules in fraction B. (e) In the world, the demand for lower boiling fractions of crude oil is greater than its supply while the supply of higher boiling fractions of crude oil is in excess. (i) Suggest a process that can produce lower boiling fractions from higher boiling fractions. racking (ii) Apart from lower boiling fractions, state another type of compound that will also be produced in the process mentioned in (i). Suggest two uses of that type of compound in daily life. Alkenes As a raw material in the manufacture of plastics To make ethanol (12 marks)

4 3. A student tried to break down a sample of medicinal paraffin (cracking) with the set-up below. (a) (i) What may solid X be? Unglazed porcelain / aluminium oxide / pumice stone (ii) What is the function of solid X? It acts as a catalyst. / It provides a red hot surface for the reaction to occur. (b) Why was not the rocksil heated directly? The medicinal paraffin will vaporize without being cracked if the rocksil is heated directly. (c) The student found that there was a layer of oily liquid on the surface of the water. Suggest what this oily liquid might be. Unreacted medicinal paraffin / liquid products (d) The student passed the gaseous products collected into bromine water. The bromine water was decolourized immediately. (i) What can you comment on the gaseous products? The gaseous products contain = or bonds. / The gaseous products are unsaturated hydrocarbons. (ii) Name the type of reaction between the gaseous products and bromine water. Addition reaction (e) After the experiment, the student tried to remove the heat source before the delivery tube was disconnected. owever, his teacher did not allow him to do so. (i) Explain why the teacher did that. Sucking back may occur. This will crack the test tube. (ii) What should the student do instead? Disconnect the delivery tube before removing the heat source. (f) Suggest two reasons to explain why cracking is an important process. racking breaks down larger hydrocarbon molecules into smaller hydrocarbon molecules (e.g. fine grade petrol) to meet the demand. It also produces alkenes which are used as raw materials in petrochemical industry (e.g. manufacture of polymers). (11 marks)

5 4. The following table shows the annual supply and demand for different fractions of petroleum in 2003 in Japan: Annual supply Annual demand Oil fraction (million tonnes) (million tonnes) (a) (b) Refinery gas 5 9 Petrol Naphtha 8 8 Kerosene Diesel oil eavy oil Explain why the annual demand for petrol was greater than that for kerosene. Petrol is a fuel for motor vehicles. The rapid growth in the number of motor vehicles makes the demand for petrol greater. racking is used to convert oil fractions in excess to oil fractions that are insufficient. (i) (1) What is the meaning of the term cracking? racking is the breaking down of larger hydrocarbon molecules into smaller hydrocarbon molecules. (2) What are the conditions for cracking? eating under high pressure / eating in the presence of catalyst at a lower temperature (ii) Draw a labelled diagram to show the experimental set-up for cracking in laboratory. (2 marks for correct set-up; 1 mark for correct method to collect the gas) [3] (c) One of the major components in petrol is octane, (i) What is the structural formula of octane? (ii) (iii) Is octane a saturated or an unsaturated hydrocarbon? Explain briefly. Saturated hydrocarbon It does not contain any carbon-carbon multiple bonds (= or bonds). Write an equation for complete combustion of octane (l) + 25O 2 (g) 16O 2 (g) O(l)

6 (d) (iv) Suggest how you can show that octane contains hydrogen and carbon. Burn octane in air. Use a dry cobalt(ii) chloride paper to test for the gas produced. The paper turns from blue to pink, hence the gas contains water vapour. This indicates the presence of hydrogen in octane. Pass the gas given off into limewater. The limewater turns milky, hence the gas contains carbon dioxide. This indicates the presence of carbon in octane. Octane reacts with chlorine gas readily under a suitable condition. (i) What is the condition for the reaction? Under sunlight / high temperature (ii) Name the type of the reaction. Substitution reaction (iii) an we use the reaction to prepare 1-chlorooctane? Explain briefly. No. A mixture of products (e.g. 2-chlorooctane, 3-chlorooctane and etc) is produced in the reaction. (18 marks)

7 5. (a) Some of the following molecules belong to the same homologous series: A: D: (b) B: O O O O : F: 3 7 E: O 3 O 3 O O O 3 (i) What is the meaning of homologous series? A homologous series is a family of carbon compounds (organic compounds) with the same general formula and functional group. (ii) Which of the above compounds belong to the same homologous series? A, and F [2] (iii) Name compounds A and B. A: methanoic acid B: butane (iv) A mixture of bromine vapour and compound B is exposed to sunlight. State the observation and write a chemical equation for the reaction. The orange bromine vapour is decolourized (g) + Br 2 (g) 4 9 Br(l) + Br(g) Propene and but-2-ene belong to the same homologous series. (i) (1) Draw the electron diagram of propene. O (ii) (iii) (2) Write the structural formula of but-2-ene. Explain whether the combustion of propene or but-2-ene would produce a less sooty flame. Propene burns with a less sooty flame because it has a lower carbon to hydrogen ratio. Apart from combustion and reaction with halogens, describe a chemical test to distinguish between compound B and but-2-ene. Write down the equation for the reaction involved. Add acidified potassium permanganate solution to the compounds. But-2-ene decolourizes the solution while butane does not. 3 = 3 + [O] + 2 O 3 (O)(O) 3 (13 marks)

8 6. A student wanted to investigate the properties of propene and but-1-ene. (a) (i) Write the structural formulae of propene and but-1-ene. Propene: But-1-ene: [1 x 2] (ii) State one difference between the physical properties of propene and but-1-ene. Propene has a lower boiling point than but-1-ene. (iii) State one difference between the chemical properties of propene and but-1-ene. Propene burns with a less sooty flame than but-1-ene. (iv) The student found that both propene and but-1-ene reacted readily with bromine in 1,1,1-trichloroethane. (1) What would be observed when bromine in 1,1,1-trichloroethane was added to propene or but-1-ene? Bromine in 1,1,1-trichloroethane turned from orange to colourless. (2) Write the equation for the reaction involved. (b) (3) Name the type of reaction involved. Addition reaction The student then tried to determine the molecular formula of a hydrocarbon W with the following set-up: A known mass of W was heated in excess oxygen. The following results were obtained. Mass of U-tube A before the experiment = g Mass of U-tube B before the experiment = g Mass of U-tube A after the experiment = g Mass of U-tube B after the experiment = g (i) What are the functions of (1) anhydrous calcium chloride and To absorb water / water vapour produced. (2) sodium hydroxide pellets? To absorb carbon dioxide produced.

9 (ii) Determine the empirical formula of W. Mass of water produced = g = g No. of moles of water produced = = mol No. of moles of hydrogen in W = x 2 = mol Mass of carbon dioxide produced = g = g No. of moles of carbon dioxide produced = = mol No. of moles of carbon in W = mol No. of moles of : no. of moles of = : = 1 : 2 The empirical formula of W = 2 (iii) If the molecular mass of W is 308, what is the molecular formula of W? Let the molecular formula of W be ( 2 ) n. n x ( x 2)= 308 n = 22 The molecular formula of W is (iv) State two assumptions for the above experiment. W burned completely in air to give carbon dioxide and water. All the water and carbon dioxide produced were absorbed completely by anhydrous calcium chloride and sodium hydroxide respectively. (Relative atomic masses: = 1.0, = 12.0, O = 16.0) (16 marks)

10 7. The following equation illustrates a possible reaction in cracking process saturated hydrocarbon A + unsaturated hydrocarbon B (a) What is the meaning of the term cracking? racking is the breaking down of larger hydrocarbon molecules into smaller hydrocarbon molecules by heat or with the help of a catalyst. (b) Each molecule of A contains 8 carbon atoms. (i) What is the molecular formula of A? 8 18 (ii) Write the structural formula of B. (c) (iii) What is the meaning of the term "unsaturated hydrocarbon"? An organic compound which contains hydrogen and carbon atoms only. Moreover, it contains carbon-carbon multiple bonds (= or bonds). (iv) To which homologous series does compound B belong? Alkene (v) Suggest a use of B. It is used as a raw material in the manufacture of petrochemical products, e.g. plastics. A is used as a fuel for motor vehicles. (i) (1) Write an equation for the complete combustion of A (l) + 25O 2 (g) 16O 2 (g) O(l) (2) Which product in combustion of A contributes to greenhouse effect? Explain why the product can cause greenhouse effect. arbon dioxide arbon dioxide absorbs radiation re-radiated from the earth surface and thus the (heat) energy is trapped. (ii) (1) Explain why car exhaust also contains carbon monoxide and nitrogen oxides. arbon monoxide: Incomplete combustion of fuel (A) occurs. Nitrogen oxides: Nitrogen combines with oxygen to form nitrogen oxides under high temperature (or spark) in the internal combustion engines of motor vehicles. (2) State one undesirable effect of carbon monoxide. It is poisonous. / It reduces the oxygen-carrying capacity of blood which will lead to dizziness and even death. (3) Explain, with the help of chemical equations, the formation of acid rain from nitrogen oxides. 2NO(g) + O 2 (g) 2NO 2 (g) 2NO 2 (g) + 2 O(l) NO 2 (aq) + NO 3 (aq) and 2NO 2 (aq) + O 2 (g) 2NO 3 (aq) (16 marks)

11 8. Town gas in ong Kong is a mixture of carbon monoxide and hydrogen. It is produced by reacting naphtha ( 5 12 ) with steam in the presence of nickel. The following flow chart shows the production process of town gas. naphtha + steam reaction chamber with nickel at 700 purifier addition of odorant town gas (carbon monoxide and hydrogen) delivered to the consumers (a) (i) State the raw material from which naphtha is obtained. Petroleum (ii) ow can naphtha be obtained from this raw material? By fractional distillation (b) Suggest the function of nickel in the reaction chamber. It acts as a catalyst. (c) Write the chemical equation for the reaction involved in the reaction chamber (l) O(g) 5O(g) (g) (d) During the reaction between naphtha and steam, hydrogen sulphide is also formed which is later removed in the purifier. Explain why it is necessary to do so. ydrogen sulphide is toxic. / Burning hydrogen sulphide may lead to the formation of sulphur dioxide (air pollutant). (e) Explain why an odorant is added in town gas. Since carbon monoxide is poisonous and hydrogen is explosive, addition of odorant makes the detection of leakage of town gas easier. (f) Suggest chemical tests to show the presence of the following compounds in town gas. (i) carbon monoxide It turns citrated blood cheery red. (ii) hydrogen It gives a pop sound with a burning splint. (g) What will be observed when town gas is passed over hot copper(ii) oxide in the absence of air? Explain briefly with the help of equations. Black copper(ii) oxide turns brown (copper). Town gas contains carbon monoxide and hydrogen which reduce copper(ii) oxide to copper. uo(s) + O(g) u(s) + O 2 (g) uo(s) + 2 (g) u(s) + 2 O(l) (h) If there is a leakage of town gas in your home, explain why (i) you have to open all the windows and doors immediately; For better ventilation (ii) you should not switch off the electrical appliances. Switching off the electrical appliances will trigger a spark which may ignite the town gas and cause an explosion. (16 marks)

12 9. (a) Liquefied petroleum gas (LPG) contains mainly butane. It is obtained from petroleum. (i) ow can LPG be obtained from petroleum? By fractional distillation of petroleum. (ii) Suggest another way from which LPG can be obtained. racking of high boiling fractions of petroleum. (iii) Write the structural formula of butane. (b) (c) (iv) Write the equation of the complete combustion of butane (g) + 13O 2 (g) 8O 2 (g) O(l) (v) Suggest a chemical test for ONE of the products in the complete combustion of butane. Any one of the following: arbon dioxide turns limewater milky. Water turns dry cobalt(ii) chloride paper from blue to pink. Water turns anhydrous copper(ii) sulphate from white to blue. (vi) Under room conditions, butane exists as a gas. State a condition under which butane can be liquefied at room temperature. igh pressure Nowadays, many taxis switch from using diesel to using LPG. Suggest a reason for such change and explain your answer briefly. LPG is a cleaner fuel than diesel. / In combustion, LPG produces less particulates or carbon monoxide than diesel. The hydrocarbon molecules in LPG have lower carbon to hydrogen ratio than those in diesel. ence, LPG undergoes complete combustion more readily. LPG is also a common domestic fuel. (i) State two safety precautions associated with the use of LPG as a domestic fuel. Any two of the following: [1 x 2] Never store excess LPG at home. heck the rubber hose frequently to see if there is any fault. Never put LPG near naked flame or under heat. Ensure good ventilation when burning LPG. (ii) State one potential hazard associated with the use of LPG as a domestic fuel. LPG may cause explosion. (iii) Kerosene was used as a domestic fuel in a few decades ago but it is almost completely replaced by LPG or town gas nowadays. State one disadvantage associated with the use of kerosene. Kerosene is a volatile liquid which catches fire easily. (13 marks)

13 10. The tables below show the melting points and boiling points of the first four members of alkanes and the first three members of alkenes. Melting point Boiling point Melting point Boiling point Alkane Alkene ( ) ( ) ( ) ( ) Methane Ethene Ethane Propene Propane But-1-ene Butane (a) Both alkanes and alkenes are hydrocarbons. What is the meaning of the term "hydrocarbon"? A hydrocarbon is a compound which contains hydrogen and carbon only. (b) Which of the above hydrocarbons exist(s) as a liquid/liquids at 100? Ethane, propane, butane, propene and but-1-ene. (c) (i) Write the general formula of alkanes. n 2n+2 (ii) State and explain the trend of the boiling points of alkanes. The boiling point of alkanes increases with the number of carbon atoms in the alkane molecules. As the number of carbon atoms in alkane molecules increases, the van der Waals forces between the molecules increase also. ence, a larger amount of energy is required to overcome the attractive forces between the molecules. (iii) State two other physical properties of alkanes which show the same trend as the boiling points. Density and viscosity increase with the number of carbon atoms in the alkane molecules. [1, 1] (d) Natural gas is a mixture of hydrocarbons. (i) What is the origin of natural gas? Natural gas was formed from marine plants and animals that lived millions of years ago. (ii) State the major component of natural gas. Methane (iii) Write an equation for the complete combustion of the major component of natural gas. 4 (g) + 2O 2 (g) O 2 (g) O(l) (e) Explain whether ethene and propene have similar chemical properties. Yes, it is because they have the same functional group (= bond). (f) (i) Both ethane and ethene can react with halogens. owever, the conditions for the reactions are different. State the difference. Ethane can only react with halogens in the presence of sunlight while ethene can react with halogens in the absence of sunlight. (ii) Suggest one reaction in which both ethane and ethene behave similarly. Write the chemical equation for the reaction involving ethane or ethene. Both ethane and ethene can react with oxygen (g) + 7O 2 (g) 4O 2 (g) O(l) / 2 4 (g) + 3O 2 (g) 2O 2 (g) O(l) (15 marks)

14 11. Installation of catalytic converters in car exhaust systems can reduce the emission of unburnt hydrocarbon ( 8 18 ) and two other air pollutants. The following shows the internal structure of a catalytic converter. (a) Name a catalyst used in catalytic converter. Platinum (b) (i) State two other air pollutants in car exhaust. arbon monoxide Nitrogen monoxide / nitrogen oxides (ii) Write chemical equations to show how these air pollutants can be removed by catalytic converter. 2O(g) + 2NO(g) catalyst 2O 2 (g) + N 2 (g) 2O(g) + O 2 (g) catalyst 2O 2 (g) (c) (i) Suggest how the emission of unburnt hydrocarbons ( 8 18 ) can be reduced by the installation of catalytic converters. The hydrocarbon is oxidized by air to give carbon dioxide and water. (ii) Write a chemical equation for the reaction involved (l) + 25O 2 (g) catalyst 16O 2 (g) O(l) (d) (i) Suggest ONE reason why unleaded petrol should be used in motor vehicles fitted with catalytic converters. Lead compounds can poison the catalyst in catalytic converter. (ii) State another advantage of using unleaded petrol in motor cars. To eliminate the damage to our nervous system (or causing lung diseases). (e) Even if all the above air pollutants are removed, the car exhaust still causes environmental problems. Explain why. ar exhaust contains a large amount of carbon dioxide which causes the greenhouse effect. or, ar exhaust contains particulates which damage our respiratory system. (f) Apart from installing catalytic converters, suggest ONE method to reduce air pollution caused by motor cars. Use electric cars. / Use petrol of higher-grade. (13 marks)

15 12. The following experimental set-up is used to investigate the components in car exhaust. (a) (i) Name liquid X. Water (ii) Suggest a test to identify liquid X. Water turns dry cobalt(ii) chloride paper from blue to pink. / Water turns anhydrous copper(ii) sulphate from white to blue. (b) (i) What is the function of limewater? To test the presence of carbon dioxide in car exhaust gas. (ii) State the observation and write a chemical equation for the reaction involved. Limewater turns milky. O 2 (g) + a(o) 2 (aq) ao 3 (s) + 2 O(l) (c) (i) Suggest a gas that can be tested by citrated blood. arbon monoxide (ii) Explain why this gas is present in car exhaust. It is due to the incomplete combustion of fuel. (iii) What will be observed when car exhaust is passed into citrated blood? itrated blood becomes cherry red. (iv) Suggest one way to reduce the amount of this gas in car exhaust. Install catalytic converters in cars. (d) Name the major component of gaseous mixture A. Nitrogen (e) What would be the change of the p value of water in the water trough? Explain your answer. The p value of water would be less than 7. Nitrogen dioxide in the car exhaust dissolves in water to give an acidic solution (nitric acid and nitrous acid). (f) A student wants to show the presence of carbon particulates in car exhaust gas. Suggest a method for him to do so. Place a moist filter paper near the car exhaust. The filter paper turns black in the presence of carbon particulates. (g) Suggest ONE reason why car exhaust pipes rust rapidly. ar exhaust pipe is very hot which speeds up rusting. / ar exhaust contains acidic gases which dissolve in water to form an acidic solution. Thus, rusting is speeded up. (15 marks)

16 13. Burning of fuels in factories and motor cars produces many air pollutants. (a) Sulphur dioxide is usually found in exhaust fumes from factories. (i) Explain, with the help of an equation, why sulphur dioxide is produced in factories. Fuels used in factories contain sulphur which is oxidized to sulphur dioxide in burning. S(s) + O 2 (g) SO 2 (g) (ii) Explain how sulphur dioxide affects (1) our health; Sulphur dioxide irritates our respiratory system. / Sulphur dioxide may cause lung cancer. (2) the growth of plants. Sulphur dioxide dissolves in rain water to form acid rain which raises the acidity of the soil and thus kills the plants. (iii) In ong Kong, does the car exhaust contain a large amount of sulphur dioxide? Explain briefly. No. In ong Kong, sulphur contents in petrol are very low. (iv) Suggest a chemical test for sulphur dioxide. Place a filter paper soaked with acidified potassium dichromate solution near the gas. The paper turns from orange to green. (b) ar exhaust usually contains pollutants, such as nitrogen monoxide, nitrogen dioxide, unburnt hydrocarbon, etc. (i) Explain, with the help of equations, how nitrogen monoxide and nitrogen dioxide are formed in car engines. At high temperature, nitrogen combines with oxygen to give nitrogen monoxide in car engines. N 2 (g) + O 2 (g) 2NO(g) (ii) (iii) (iv) Nitrogen monoxide further reacts with oxygen to give nitrogen dioxide. 2NO(g) + O 2 (g) 2NO 2 (g) State one environmental problem associated with the emission of oxides of nitrogen into the atmosphere. Formation of acid rain / corrosion of buildings Name a pollutant which is formed from the reaction between the oxides of nitrogen and unburnt hydrocarbon. What is the effect of this pollutant on our health? Photochemical smog. It can cause eye and bronchial irritation. State another pollutant that may be found in the car exhaust. Particulates / carbon monoxide (16 marks)

17 14. The following bar chart shows the amount of some air pollutants in city Y in 2003: (a) (i) Which air pollutant was produced in the greatest amount in motor vehicles? arbon monoxide (ii) Explain why this pollutant can be found in motor vehicles. It is produced by incomplete combustion of petrol. (iii) State one harmful effect of this pollutant. It is poisonous. / It reduces the oxygen carrying capacity of blood which will lead to dizziness and even death. (iv) Suggest a method to reduce the amount of this pollutant. Install catalytic converters in cars. (b) Emission from power stations contains a large amount of particulates. (i) State one health problem associated with particulates. They attack our respiratory system. / They may cause cancer. (ii) State one way to remove particulates from the emission. Use electrostatic precipitators. (c) (i) What can be deduced from the fact that less amount of sulphur dioxide was emitted from power stations than industries? The fuel used in power station contains less amount of sulphur than that used in industries. (ii) Sulphur dioxide dissolves in rain water to give acidic rain. (1) Write an equation for the formation of acid rain from sulphur dioxide. SO 2 (g) + 2 O(l) 2 SO 3 (aq) (2) State TWO undesirable effects of acid rain. Any two of the following: [1x 2] increase the rate of corrosion of metals / cause damages to buildings / harmful to aquatic lives / harmful to plants (iii) Suggest one measure to reduce the emission of sulphur dioxide. Use fuels with lower sulphur content / installation of scrubber systems in power stations (11 marks)

18 15. The following table shows the monthly mean p values of rain water collected from four different districts (P, Q, R and S) in city X. Monthly mean p value District of rain water (a) (b) (c) (d) (e) P 5.1 Q 4.6 R 3.9 S 5.2 The normal p value of rain water is about 5.5. Explain, with the help of an equation, why rain water is slightly acidic. arbon dioxide in air dissolves in rain water to form carbonic acid. O 2(g) + 2 O(l) 2O 3(aq) When rain water has a p value lower than 5.0, it is considered as acid rain. (i) Name TWO pollutants that contribute to the formation of acid rain. Sulphur dioxide Nitrogen dioxide (ii) Write the equations for the formation of acid rain from the two pollutants in (i). SO 2(g) + 2 O(l) 2SO 3(aq) 2NO 2(g) + 2O(l) NO 2(aq) + NO 3(aq) and 2NO 2(aq) + O 2(g) 2NO 3(aq) Which district is most likely to be an industrial area? Explain your answer. R The rain water there has the lowest p value. The problem of acid rain becomes more and more serious in city X in recent years. (i) Suggest TWO possible reasons for this phenomenon. There are more and more factories in city X. There are more and more motor vehicles in city X. (ii) Suggest TWO methods to reduce the problem of acid rain. Any two of the following: [1 x 2] Install scrubbers in factories. Install catalytic converters in motor vehicles. Use fuels with lower sulphur contents. It is found that the p value of rain water is lower in thunderstorm. Explain the phenomenon briefly. Lightning provides sufficient energy for direct combination of nitrogen and oxygen. Nitrogen monoxide formed further reacts with oxygen to give nitrogen dioxide which dissolves in rain water to give an acidic solution. (14 marks)

19 16. A student tried to investigate the p value of rain water collected in an area with an incinerator and a lot of factories. (a) ould he use methyl orange to measure the p value of rain water? Explain briefly. No. Methyl orange could only indicate whether the rain water was acidic or not. (b) Name a device he should use to measure the p value of rain water accurately. p meter / p sensor connected with a data-logger (c) e found that the p value of rain water was about 4.5. (i) Name two pollutants from factories that were responsible for the acidity of rain water. Explain why the pollutants were emitted from the factories. Sulphur dioxide The fuels used contained sulphur. Nitrogen dioxide At high temperature, nitrogen combined with oxygen to give nitrogen monoxide which was further oxidized to nitrogen dioxide. (ii) Write an equation to show the formation of acid rain from one of the pollutants in (c)(i). SO 2(g) + 2 O(l) 2SO 3(aq) / 2NO 2(g) + 2O(l) NO 2(aq) + NO 3(aq) (iii) The rain water led to faster corrosion of buildings made of marble. (1) Name the major component of marble. alcium carbonate (2) Explain, with the help of an ionic equation, why the buildings corroded much faster than normal. alcium carbonate reacted with acid to give carbon dioxide and soluble calcium salt. + 2 (aq) + ao 3(s) a 2+ (aq) + O 2(g) + 2O(l) (iv) When 1,1,1-trichloroethane was burnt in incinerator, several pollutants were produced. (1) Apart from the pollutants in (c)(i), name one pollutant which was also emitted from the incinerator. ydrogen chloride or, arbon soot or, arbon monoxide (2) State one harmful effect of this pollutant. Formation of acid rain or, Irritate our respiratory system or, Poisonous / reduce the oxygen-carrying capacity of blood which would lead to dizziness and even death. (13 marks)

20 17. The following bar chart shows the estimated time when the fossil fuels are used up: (a) (b) Fossil fuel A is petroleum. (i) Why is petroleum known as a fossil fuel? Petroleum was formed from remains of marine plants and animals that lived millions of years ago. (ii) Identify fossil fuels B and. B: natural gas : coal (iii) State two reasons why petroleum is more commonly used in industries than fossil fuel. Petroleum produces less pollutants than coal in combustion. Petroleum is more convenient to use. (iv) Why is it important to conserve fossil fuels? Fossil fuels are non-renewable. / The reserve of fossil fuels is limited. Nowadays, many countries have been developing alternative energy sources instead of using fossil fuels. (i) Apart from conserving fossil fuels, suggest one reason why it is necessary to develop alternative resources of energy. Burning of fossil fuels produces a lot of air pollutants. / Burning of fossil fuels causes greenhouse effect. / The price of fossil fuel is controlled by a few countries. (ii) There are several alternative sources of energy. For each of the following sources of energy, state ONE advantage and ONE disadvantage of using each of them as an alternative to fossil fuels. (1) solar energy Advantage: The supply of sunlight is unlimited. / Less pollutants are produced. Disadvantage: The supply of sunlight is not reliable. (2) geothermal energy Advantage: It is cheaper in the long run. / It is a clean energy source. Disadvantage: It is difficult to find suitable sites to set up plants. (3) hydroelectric power Advantage: The supply of this energy source is unlimited. / It produces less pollutants. Disadvantage: It is difficult to find suitable sites to set up plants. / The cost of building

21 a huge dam is very expensive. (13 marks) 18. Fossil fuels are the world s major sources of energy. In burning of fossil fuels, a large amount of carbon dioxide is released into the atmosphere. (a) Suggest a natural process by which carbon dioxide in the atmosphere is used up. Photosynthesis (b) Explain why carbon dioxide is important to living things on the Earth. It maintains the temperature on the Earth so that the Earth is suitable for living. (c) Suggest TWO consequences that are resulted from the excess emission of carbon dioxide. Excess emission of carbon dioxide can cause greenhouse effect and global warming. It will lead to melting of polar icecaps and hence flooding in many parts of the world. It will also change the climate pattern. (d) Fossil fuels are considered as non-renewable energy sources. Explain the meaning of the term non-renewable energy sources. The energy sources which are used up at a faster rate than the rate at which they can be produced on Earth. (e) Alternative energy sources such as nuclear energy become more and more important in many countries. (i) Is nuclear power a non-renewable energy source? Yes. (ii) State ONE advantage and ONE disadvantage of using nuclear power as an alternative to fossil fuels. Advantage: Nuclear power is cheaper in the long run. / Nuclear power is a clean energy source. / Nuclear power produces less pollutants. Disadvantage: It is expensive to set up a nuclear power plant. / It is difficult to dispose of radioactive wastes. / Leakage of radioactive substances is highly dangerous. (f) In some farms, animal wastes (manure) are collected and are allowed to decompose in the absence of air. A gas X is produced which can also be used as an alternative to fossil fuels. (i) Name gas X. Methane (ii) Write an equation for the complete combustion of gas X. 4 (g) + 2O 2 (g) O 2 (g) O(l) (iii) State one disadvantage of using animal wastes as fuel. The production rate of methane is low. / The animal wastes can be used as fertilizers instead of as fuels. (iv) State one environmental problem associated with the emission of gas X into the atmosphere. Methane contributes to the greenhouse effect. (12 marks)

22 19. The following flow chart shows the industrial production of ethanol: process 1 Petroleum heavy fraction of petroleum process 2 Ethanol catalytic hydration ompound B (a) (i) Name process 1. Fractional distillation of petroleum (ii) At which part of a petroleum refinery does process 1 take place? Fractionating tower (b) (i) Name process 2. racking (ii) Draw a labelled diagram to show the experimental set-up for process 2 in the laboratory. (1 mark for correct set-up; 1 mark for correct method to collect the gas; 1 mark for correct catalyst) [3] (c) (i) What is compound B? Ethene / 2 4 (ii) Assuming that the heavy fraction of petroleum is and only a hydrocarbon and compound B are formed in process 2, write an equation for the reaction involved (l) 2 4 (g) (l) (d) atalytic hydration is employed to convert compound B into ethanol. (i) Write the chemical equation for the reaction involved. = (g) + O(g) catalyst O(g) (e) 300,65atm (ii) Suggest a way to obtain pure ethanol if the ethanol produced is contaminated with a trace amount of water. Using drying agent (e.g. calcium oxide or anhydrous calcium chloride). (iii) an the ethanol produced in this way be used to make wine? Explain briefly. No. It is because the ethanol is contaminated with some toxic impurities, e.g. methanol. In some agricultural countries, ethanol can also be produced by another process. Moreover, a mixture of petrol and ethanol is often used as a fuel for motor cars in such countries.

23 (i) What is the process? Fermentation (ii) Using such a mixture of petrol and ethanol would cause less pollution than burning petrol alone. Explain why. Ethanol burns more completely than petrol / produces less amount of soot. (iii) Suggest one advantage and one disadvantage of using a mixture of petrol and ethanol as fuel for motor cars in such countries. Advantage: The production price of ethanol in such countries is low. Disadvantage: The energy value of ethanol is lower than that of petrol. (16 marks)

24 20. A student tried to produce ethanol with the following set-up: (a) Name the process for the production of ethanol shown in the diagram. Fermentation (b) What was solution X? A mixture of sugar solution and yeast. [1, 1] (c) Write the equation for the reaction involved in the conical flask O 6(aq) 225O(aq) + 2O 2(g) (d) State any observable change(s) in limewater after a few days. Explain briefly with the help of an equation. Limewater turned milky. It is because carbon dioxide was produced during fermentation. The carbon dioxide reacted with calcium hydroxide solution (limewater) to give insoluble calcium carbonate (milky). (e) a(o) 2(aq) + O 2(g) ao 3(s) + 2O(l) The student found that the concentration of ethanol produced remained at 9% after a week. (i) Explain this phenomenon. When the concentration of ethanol increased to a certain level, the yeast died. Fermentation would stop. (ii) ow can he obtain a higher concentration of ethanol from the reaction mixture in the conical flask? Fractional distillation (f) After the process in (e)(ii), the student added the concentrated ethanol to acidified potassium dichromate solution. (i) Name the acid used to acidify potassium dichromate solution. Sulphuric acid / 2SO 4 (ii) What would be observed when concentrated ethanol was mixed with acidified potassium dichromate solution? The colour of the solution would change from orange to green. (iii) Write an equation for the reaction involved. 3 2 O + 2[O] 3 OO + 2 O / 3 2 O [o] 3 OO (g) (i) State one health hazard associated with the excessive drinking of alcoholic beverages. Excess drinking can cause brain damage / depression / liver damage / stomach ulcer. (ii) Apart from making alcoholic beverages, state one use of ethanol in daily life. As fuels / solvents / disinfectants (15 marks)

25 21. An alcoholic drink can be produced by fermentation of apple. After fermentation, the resulting solution contains 10% of ethanol. (a) (i) Describe how the alcoholic drink can be produced by fermentation of apple in the laboratory. Add some apples to a mixture of water and yeast. [1, 1] The mixture is then stored in a container in the absence of air for several days. (ii) Draw a labelled diagram to show how fermentation can be carried out in the laboratory. [2] (b) Apart from ethanol, state one product which is also produced in fermentation. arbon dioxide (c) (i) Suggest a process which can increase the concentration of ethanol in the solution obtained. Distillation / fractional distillation (ii) Draw a labelled diagram of the laboratory set-up for the process in (c)(i). (d) (e) (f) (1 mark for correct diagram, 1 mark for correct labelling, 1 mark for correct direction of water flow) [3] Acidified potassium dichromate solution can be used to test the presence of ethanol in the breath of a drunk driver. Explain the principle behind. If the driver has taken in excess alcohol, his breath contains a high concentration of ethanol. When the breath is passed into acidified potassium dichromate solution, the solution turns from orange to green. Explain why alcoholic drink becomes sour after it is exposed to air for several days. Ethanol is oxidized by oxygen in the air to ethanoic acid. State one advantage and one social problem associated with alcoholic drinking. Advantage:

26 Drinking small amount of alcoholic drink can cause thinning of blood / reduce the risk of heart disease. Social problem associated with the excessive alcoholic drinking : Violence / dangerous driving (16 marks)

27 22. onsider the following flow chart. Process 1 Process 2 X ethanol ethanoic acid (a) ester W X is a hydrocarbon. (i) Give the systematic name of X. Ethene (ii) Suggest a process from which X is obtained industrially. racking of petroleum (iii) Name process 1. Write the equation for the reaction involved. atalytic hydration catalyst 2 = 2 (g) + 2 O(g) 300,65atm 3 2 O(g) (iv) X reacts with bromine in 1,1,1-trichloroethane readily. State the observation and write the chemical equation for the reaction involved. Bromine solution turns from orange to colourless. 2= 2(g) + Br 2(in organic solvent) 2Br2Br(in organic solvent) (b) (i) Suggest a reagent that can be used to convert ethanol into ethanoic acid. Acidified potassium dichromate solution / acidified potassium permanganate solution (ii) What is the type of reaction involved in process 2? Explain your answer briefly. Redox reaction / Oxidation 2- The oxidation number of r in r2o7 decreases from +6 to +3. / (c) The oxidation number of Mn in MnO4 - decreases from +7 to +2. When ethanol reacts with ethanoic acid in the presence of catalyst Y, ester W is formed. (i) Name Y. oncentrated sulphuric acid (ii) Give the structural formula of W. (iii) O O Name the type of the reaction involved. Esterification

28 (iv) Draw a labelled diagram of the experimental set-up for the reaction. (Deduct 1 mark for incorrect indication of direction of water flow; closed system; no indication of heat; incomplete indication of reagents.) [2] (14 marks)

29 23. A student tried to produce methyl ethanoate with the following set-up: (a) (i) Name A and B. A: methanol / ethanoic acid B: ethanoic acid / methanol (ii) What was the function of concentrated sulphuric acid in the above experiment? It acted as a catalyst. (iii) Write an equation for the reaction involved. 3 O(l) + 3 OO(l) 3 OO 3 (l) + 2 O(l) (iv) Write the structural formula of methyl ethanoate. (b) (c) O O The reaction mixture had been heated under reflux for an hour. (i) Explain why the reaction mixture was heated during the reaction. To increase the rate of reaction. (ii) Why was the reaction mixture heated in hot water bath instead of in naked flame? Methanol is highly flammable and it catches fire easily. (iii) Name apparatus P. State its function. Reflux condenser To prevent the loss of reactants and products. (iv) State the direction of water flow in P. Water flows from the lower inlet to the upper outlet. (v) What was the function of anti-bumping granules in the experiment? To ensure smooth heating After the reaction, the reaction mixture was poured into saturated sodium chloride solution. (i) State two observable changes after the reaction mixture was added to saturated sodium chloride solution. A sweet smell was detected. Two layers were observed. (ii) Suggest a way to obtain methyl ethanoate from the resulting solution. Use a dropper / separating funnel to remove the upper layer (methyl ethanoate).

30 (d) Suggest the systematic name of an ester which has the same molecular formula as methyl ethanoate. Ethyl methanoate. (15 marks)

31 24. A student tried to prepare an ester by mixing 3.68 g of ethanol and 3.0 g of ethanoic acid with the following set-up: (a) (b) (c) (d) The student found that no ester was formed after the reaction mixture was heated under reflux for an hour. Suggest how he could make the experiment feasible. Add concentrated sulphuric acid to the reaction mixture. After the student made the modification, he could produce an ester successfully. (i) Write an equation for the production of ester in the above experiment. 3OO(l) + 32O(l) 3 OO2 3(l) + 2O(l) (ii) Give the systematic name of the ester obtained in this experiment. Ethyl ethanoate (iii) What mass of ester would be obtained if the conversion was 100%? No. of moles of 32O = 3.68 (12 x x ) = 0.08 mol No. of moles of 3OO = 3 (12 x x x 2) = 0.05 mol According to the equation, the mole ratio of 32O to 3OO = 1 : 1. 3OO is the limiting reactant. Mass of 3OO2 3 produced = 0.05 x (12 x x x 2) = 4.4 g (iv) The student found that only 1.8 g of ester was obtained. (1) What was the percentage yield of the reaction? Percentage yield = 1.8 x 100% 4.4 = 40.9% (2) Suggest why the conversion was not 100%. The reaction is reversible. Suggest a hazard warning label that should be displayed on a bottle of ester. Flammable Ester is a common solvent for molecular substances but not ionic compounds. (i) Explain why esters cannot dissolve ionic compounds. The attractive forces between ions in ionic compounds are strong ionic bonds while the attractive forces between ethyl ethanoate molecules are weak van der Waals forces. Strength of attraction between ions is not comparable with that between molecules.

32 (ii) State another common use of esters in our daily lives. They are used as artificial flavourings / in perfumes and cosmetics. (Relative atomic masses: = 1.0; = 12.0; O = 16.0) (13 marks) 25. The following table shows some chemical properties of ethanol: Experiment Result 1. Ethanol is heated with acidified potassium The colour of the solution changes from permanganate solution. purple to colourless. ompound A is formed which turns blue litmus paper red. 2. Burning of ethanol with sufficient supply Blue flame is observed. of air. 3. Ethanol and compound B are mixed and the reaction mixture is... (a) onsider experiment 1. (i) What is A? Write the structural forumla of A. ompound with five carbons (with pleasant smell) is formed. Ethanoic acid / OO 3 O O (ii) Write an equation for the reaction involved. 3 2 O + 2[O] 3 OO + 2 O / 3 2 O [o] 3 OO (iii) Explain, in terms of oxidation number, whether potassium permanganate is reduced or oxidized. - Oxidation number of Mn in MnO4 decreases from +7 to +2, hence MnO4 - is reduced. (iv) What will be observed when A is added to sodium carbonate solution? Write a chemical equation for the reaction involved. Effervescence occurs. 2 3 OO(aq) + Na 2 O 3 (s) 2 3 OONa(aq) + 2O(l) + O 2(g) (b) (i) Is combustion of ethanol an exothermic or an endothermic reaction? Exothermic reaction (ii) Write an equation for complete combustion of ethanol. 3 2 O(l) + 3O 2(g) 2O2(g) + 32O(l) (iii) Suggest a chemical test for each of the products formed in the complete combustion of ethanol. Water: It turns dry cobalt(ii) chloride paper from blue to pink. / It turns anhydrous copper(ii) sulphate from white to blue. arbon dioxide: It turns limewater milky. (iv) Explain why, under the same conditions, ethanol usually burns with a blue flame while petrol does not. Ethanol molecules have shorter carbon chains than molecules in petrol.

33 (c) (i) Part of the procedure of experiment 3 is missed. omplete the missing part. heated under reflux in the presence of concentrated sulphuric acid. (ii) Name B. Propanoic acid (iii) What type of compound is? Give the systematic name of. Type of compound: ester ompound : ethyl propanoate (17 marks) 26. W, X, Y and Z were four unlabelled bottles, each containing one of the following chemicals: butanoic acid, pent-1-ene, ethyl ethanoate and butan-1-ol. A student tried to identify them with the following chemical tests. Test Result 1. Add bromine in 1,1,1-trichloroethane to the Bromine was decolorized by X only. chemicals. 2. Add sodium hydrogencarbonate solution to Effervescence occurred in Z only. the chemicals. 3. Add acidified potassium dichromate solution to the chemicals. W turned acidified potassium dichromate solution from orange to green. There was no observable change in other chemicals. (a) Identify W, X and Y. W: butan-1-ol X: pent-1-ene Y: ethyl ethanoate (b) Name the type of reaction in test 1. Write the equation for the reaction involved. Addition reaction 3 7 = 2(l) + Br 2(in 1,1,1-trichloroethane) 37Br2Br(in 1,1,1-trichloroethane) (c) Write a chemical equation for the reaction in test OO(aq) + NaO 3(aq) 37OONa(aq) + O 2(g) + 2O(l) (d) onsider test 3. (i) Explain, with the help of a half-equation, why the acidified potassium dichromate solution changed from orange to green. Orange dichromate ions were reduced by butan-1-ol to green chromium(iii) ions r2o 7 (aq) + 14 (aq) + 6e 2r (aq) O(l) (ii) Explain whether acidified potassium permanganate solution can be used instead of acidified potassium dichromate solution to distinguish W from other chemicals. No. It is because both butan-1-ol and pent-1-ene can decolourize acidified potassium permanganate solution. (e) Apart from test 2, suggest another chemical test for Z. Write an equation for the reaction involved. Add magnesium. Gas bubbles (hydrogen gas) are given off. Mg(s) OO(aq) (37OO) 2Mg(aq) + 2(g) or, Reflux with ethanol (or other alcohols) in the presence of concentrated sulphuric acid. Fruity smell is detected. 3 7 OO(aq) + 25O(aq) 37OO2 5(aq) + 2O(l)

34 (f) Explain, in general, why W, X, Y and Z have different chemical properties. They have different functional groups. (13 marks)

35 27. "racking is an important industrial process." Explain why cracking is an important industrial process. Briefly describe, with the help of a diagram, how this process can be carried out in school laboratory. (You are required to give a paragraph-length answer. In this question, 7 marks will be awarded for chemical knowledge and 3 marks for effective communication.) (10 marks) racking is an important industrial process because it breaks down less useful larger hydrocarbon molecules into more useful smaller hydrocarbon molecules (e.g. petrol). Moreover, cracking can produce alkene which is a raw material in the manufacture of many petrochemical products, e.g. plastics and detergents. The following set-up can be used for cracking in the laboratory: [2] Rocksil is soaked with medicinal paraffin. eat the pumice stones (if the medicinal paraffin is heated directly, it will vaporize and pass through the catalyst rapidly without being cracked. Thus, the catalyst is heated instead).. The medicinal vapour is allowed to pass over heated pumice stones for cracking. Gaseous products (smaller hydrocarbons) are collected by displacement of water. (3 marks for effective communication)

36 28 Discuss global warming. Your essay should include the causes of and the problems associated with global warming. Suggest TWO possible ways to reduce the problems. (You are required to give a paragraph-length answer. In this question, 6 marks will be awarded for chemical knowledge and 3 marks for effective communication.) (9 marks) Infra-red radiation is trapped by carbon dioxide and other greenhouse gases (e.g. methane, ozone and F) in the atmosphere, keeping the Earth warm. Moreover, due to the burning of excess fossil fuels (or over-deforestation) in recent decades, the concentration of carbon dioxide in the atmosphere increases rapidly. ence, the temperature of the Earth s surface rises a lot. Problems associated with global warming: [1 x 2] - Icecaps at the North Pole and South Pole melt. Thus sea levels will rise. This will cause flooding in low-lying coastal areas. - limate patterns will change. This will affect the supply of food and agriculture. Ways to reduce the problems of global warming (any two of the following): [1 x 2] - Reduce the use of fossil fuel by using alternative sources of energy. - Reduce deforestation. - Forestation. (3 marks for effective communication) 29. State pros and cons of using ethanol as a fuel for motor cars. (You are required to give a paragraph-length answer. In this question, 6 marks will be awarded for chemical knowledge and 3 marks for effective communication.) (9 marks) Advantages of using ethanol as a fuel for motor cars (any three of the following): [1 x 3] - It burns more completely than petrol and thus it is a cleaner fuel. - It is a cheaper fuel in agricultural countries. - Gasohol (a mixture of ethanol and petrol) can be used readily in conventional engines in motor cars. - It can burn directly as a fuel and no additives are required to improve its efficiency. Disadvantages of using ethanol as a fuel for motor cars (any three of the following):[1 x 3] - The energy value of ethanol is lower than that of petrol. - It is more expensive than petrol in many countries. - Large agricultural areas are needed for the growing of sugar cane. - ar engines have to be modified to use pure ethanol. - Toxic substances, e.g. ethanal ( 3 O), are produced in the burning of ethanol. (3 marks for effective communication)