QUESTIONSHEETS APPLIED ORGANIC CHEMISTRY I DISTILLATION OF PETROLEUM EPOXYETHANE AND ETHANE-1,2-DIOL HALOALKANES AS SYNTHETIC INTERMEDIATES

Transcription

1 CHEMISTRY QUESTIONSHEETS AS Level AS TOPIC 15 APPLIED ORGANIC CHEMISTRY I Questionsheet 1 Questionsheet 2 Questionsheet 3 Questionsheet 4 Questionsheet 5 Questionsheet 6 Questionsheet 7 Questionsheet 8 Questionsheet 9 Questionsheet 10 Questionsheet 11 Questionsheet 12 DISTILLATION OF PETROLEUM CRACKING FUELS EPOXYETHANE AND ETHANE-1,2-DIOL ADDITION POLYMERS HALOALKANES AS SYNTHETIC INTERMEDIATES CFCs USES OF OTHER ORGANIC HALOGENOCOMPOUNDS FERMENTATION SYNTHETIC ETHANOL PROCESS ETHANOL AS A FUEL DISPOSAL OF ORGANIC WASTE 17 marks 17 marks 19 marks 16 marks 19 marks 22 marks 16 marks 14 marks 14 marks 16 marks 16 marks 17 marks Authors Trevor Birt Donald E Caddy Andrew Jones Adrian Bond Editors John Brockington Stuart Barker John Brockington Kevin Frobisher Andy Shepherd Stuart Barker Curriculum P ress Curriculum Press Licence Agreement: Paper copies of the A-Level Chemistry Questionsheets may be copied free of charge by teaching staff or students for use within their school, provided the Photocopy Masters have been purchased by their school. No part of these Questionsheets may be reproduced or transmitted, in any other form or by any other means, without the prior permission of the publisher. All rights are reserved. This license agreement is covered by the laws of England and Wales Curriculum Press March Curriculum Press Bank House 105 King Street Wellington Shropshire TF1 1NU

2 TOPIC 15 Questionsheet 1 DISTILLATION OF PETROLEUM a) (i) Give a brief description of the chemical composition of petroleum (crude oil). Petroleum from the Middle East is described as heavy crude oil, in contrast to that from the North Sea, which is light crude. What do these descriptions mean in terms of composition? b) The first major treatment that petroleum receives at an oil refinery is fractional distillation, to separate it into fractions. (i) What is a fraction? On what physical property of compounds is the separation based? c) In the space below, sketch a plant used in the primary distillation of petroleum. [3] d) Label your diagram in c) to show clearly: (i) the temperature gradient, [1] where at least four major fractions are drawn off. [4] e) Name the material drawn off from the bottom of the plant, and give one of its major uses. Material... [1] Use... [1] f) What is the major difference between the operation of fractional distillation in industry and in the laboratory? TOTAL / 17

3 TOPIC 15 Questionsheet 2 CRACKING a) Textbooks say that most naphtha (heavy gasoline) is cracked to give more useful substances. (i) Why cannot naphtha be used as a fuel in motor cars? A typical constituent of naphtha is decane, C 10 H 22. Write two chemical equations to show likely ways in which decane will undergo cracking. (iii) Give three ways in which the products of cracking are more useful [3] b) Both thermal cracking and catalytic cracking are employed in the oil industry. Compare these two processes by completing the following table. Thermal cracking Catalytic cracking Conditions Type of bond breaking Type of reaction intermediate Principal products [9] c) Explain why, in catalytic cracking, catalysts are considered as variable costs rather than fixed costs, even though catalysts are not consumed in catalysed reactions. TOTAL / 17

4 TOPIC 15 Questionsheet 3 FUELS a) Methane and octane have standard enthalpies of combustion of kj mol -1 and kj mol -1 respectively. (i) For each of these compounds, calculate the enthalpy change per gram of fuel combusted. Methane... [1] Octane... [1] In the light of your answer to (a) (i), give two reasons why motor cars are more likely to be fuelled by octane than by methane. b) Hydrogen gas has been suggested as a fuel. Suggest one disadvantage and one advantage compared to other fuels. Disadvantage... Advantage... c) (i) The combustion efficiency of a fuel can be raised by adding benzene or tetraethyllead. State one disadvantage of each. Benzene... [1] Tetraethyllead... [1] Inefficient combustion of hydrocarbon fuels can give a toxic neutral gas. Give the name and formula of this pollutant Name... [1] Formula... [1] (iii) State two other environmental problems arising from using hydrocarbon fuels and name the product in question Problem... [1] Product... [1] Problem... [1] Product... [1] TOTAL (Continued...) /

5 TOPIC 15 Questionsheet 3 Continued FUELS d) (i) In what essential respect does a diesel engine differ from a petrol engine? In what essential respect does diesel fuel differ from petrol? (iii) What pollutant, believed to be a serious health hazard, is present to a much greater extent in diesel exhaust fumes than in petrol exhaust fumes? e) Sunflower oil can be adapted to use as biodiesel. It is called a carbon neutral fuel whereas petrol leaves a carbon footprint. Explain each of these terms. TOTAL / 19

6 TOPIC 15 Questionsheet 4 EPOXYETHANE AND ETHANE-1,2-DIOL Epoxyethane and ethane-1,2-diol are two important compounds manufactured from ethene. a) (i) Write a balanced equation, with state symbols, for the conversion of ethene to epoxyethane by reaction with a large excess of oxygen at high pressure. What catalyst is used for this process? (iii) Why does a high pressure give a better yield of epoxyethane? (iv) Although all high pressure processes carry the risk of an explosion, the hazard is particularly severe in this process. Why? b) Epoxyethane can be hydrated to give ethane-1,2-diol, and reacted with alcohols to give products which can be used as solvents and plasticisers. (i) Despite the fact that epoxyethane is an ether, and ethers are generally inert, epoxyethane is a very reactive compound. How do you account for this? Write a chemical equation for one molecule of epoxyethane reacting with one molecule of methanol. [1] (iii) Write an equation for the product of b) reacting with a further molecule of epoxyethane to give a secondary product. [1] TOTAL (Continued...) /

7 TOPIC 15 Questionsheet 4 Continued EPOXYETHANE AND ETHANE-1,2-DIOL c) Ethane-1,2-diol ( glycol ) is used as an antifreeze in car radiators. Although monohydric alcohols can also be used for the purpose, ethane-1,2-diol is particularly suitable. Why is this? d) Ethane-1,2-diol is also used for the production of the polyester Terylene, by condensation polymerisation with benzene-1,4-dicarboxylic acid ( terephthalic acid ). (i) What is meant by the term condensation in this context? Write down the structural formula of benzene-1,4-dicarboxylic acid. [1] (iii) Explain why a polyester is formed, rather than a simple ester. e) State one other major use of ethane-1,2-diol. TOTAL / 16

8 TOPIC 15 Questionsheet 5 ADDITION POLYMERS a) Define the terms monomer, addition polymer and high polymer. Monomer... [1] Addition polymer... [1] b) (i) What is the structural difference between low density poly(ethene) (LDPE) and high density poly(ethene) (HDPE)? Give two advantages of HDPE over LDPE. c) (i) Perspex is an addition polymer with the following structural formula: CH 2 CH 3 C COOCH 3 n Write down the structure of the monomer. [2] Natural rubber is made by the polymerisation of 2-methylbut-2-ene. Write down the structure of natural rubber, showing clearly one repeat unit in the polymer chain. [2] TOTAL (Continued...) /

9 TOPIC 15 Questionsheet 5 Continued ADDITION POLYMERS d) What is the common commercial name for poly(chloroethene)? e) How can you account for the fact that poly(chloroethene) is much stiffer than poly(ethene)?... [3] f) Would you use poly(ethene) or poly(chloroethene) to make a container for concentrated aqueous sodium hydroxide? Explain your choice.... [4] g) State two problems which are associated with the disposal of waste polychloro(ethene) [2] TOTAL / 19

10 TOPIC 15 Questionsheet 6 HALOALKANES AS SYNTHETIC INTERMEDIATES Haloalkanes are versatile intermediates in organic synthesis. The following flow diagram shows in outline how bromoethane (compound A) can be converted to compounds B, C, D, E, F and G. C C 2 H 6 SO 4 Reagent(s) Conditions Reagent(s) Conditions B C 2 H 4 Reagent(s) Conditions D C 2 H 6 O Reagent(s) Conditions Reagent(s) Conditions A C 2 H 5 Br Reagent(s) Conditions Reagent(s) Conditions E C 2 H 4 O 2 F C 3 H 5 N Reagent(s) Conditions G C 3 H 6 O 2 a) Give the names of compounds B, C, D, E, F and G. B =... C =... D =... E =... F =... G =... [6] b) Complete the diagram by inserting reagents and conditions for the conversions shown. [16] TOTAL / 22

11 TOPIC 15 Questionsheet 7 CFCs A major environmental problem associated with the large scale use of halogenoalkanes is their effect on the ozone layer in the upper atmosphere. CFCs are of particular concern. a) (i) What do the letters CFC stand for? Write down the structural formula of 1,1-dichloro-2,2-difluoroethane, commonly referred to as CFC 12. (iii) In the past CFCs have been widely used as aerosol propellants, but their use for this purpose has been largely abandoned. Give two other applications. b) Trioxygen (commonly called ozone ) in the upper atmosphere decomposes into dioxygen by reaction with atomic oxygen, as shown by Equation 1. O 3 + O 2O 2 Equation 1 In the absence of a catalyst the reaction is slow, but in the presence of CFCs a somewhat faster free radical chain reaction can occur. [1] (i) What is a free radical? The chain reaction is initiated by the homolytic fission (by UV light) of a C Cl bond. Explain why chlorine free radicals are produced, rather than fluorine free radicals. (iii) The initiation stage is followed by a propagation stage involving two reactions. Each of these uses up a free radical and produces another sort of free radical. Each of them also consumes a molecule of reactant (see Equation 1) and gives a molecule of the final product. Write equations for these two propagation reactions. Reaction 1... [1] Reaction 2... [1] TOTAL (Continued...) /

12 TOPIC 15 Questionsheet 7 Continued CFCs (iv) Explain why one chlorine free radical could react with literally thousands of ozone molecules. (v) Why is the rate of decomposition of ozone still low, even in the presence of CFCs? c) (i) Briefly explain the serious health hazard posed by depletion of the ozone layer. What other environmental problem do CFCs present, even at low concentrations? (iii) Suggest one substance which could be used as a replacement for CFCs in most applications. TOTAL / 16

13 TOPIC 15 Questionsheet 8 USES OF OTHER ORGANIC HALOGENOCOMPOUNDS a) Chlorinated hydrocarbons, such as tetrachloromethane and tetrachloroethene, are widely used in industry and commerce as degreasing solvents. Tetrachloromethane (carbon tetrachloride) is used in the engineering industry to degrease metal components before they are painted or electroplated. (i) Why is the degreasing of components so important? State what precaution must be taken when using tetrachloromethane, and give the reason for this. Precaution... [1] Reason... [1] (iii) What is the commercial (i.e. high street ) application of tetrachloroethene ( perchloroethylene )? b) (i) Unplasticised polyvinyl chloride (UPVC), otherwise known as poly(chloroethene), is used for manufacturing doors and window frames. State three advantages of UPVC for this purpose over traditional building materials, such as wood.... [3] Name another halogen-containing plastic and state its use. Name... [1] Use... [1] c) The adoption of organic chlorocompounds as herbicides and pesticides has been due in part to the strength of the C Cl covalent bond. (i) What advantage does this offer? What is the associated disadvantage? d) Bromochlorodifluoromethane (BCF) is commonly used in fire extinguishers. (i) Explain how this compound works in putting out fires. Why is it much safer, when fighting electrical fires, to use BCF rather than a foam extinguisher? TOTAL / 14

14 TOPIC 15 Questionsheet 9 FERMENTATION Although ethanol for industrial purposes is manufactured in the UK by the hydration of ethene, the anaerobic fermentation of sugar solutions is used for the production of alcoholic beverages. Fermentation is carried out in the presence of yeast, which acts as the source of an enzyme called zymase. a) (i) Name a simple sugar which could be fermented to produce ethanol. What is meant by the term anaerobic? (iii) Write a balanced equation for the fermentation of a simple sugar. (iv) What is the role of zymase in the fermentation? b) (i) Draw a labelled diagram of a simple apparatus which could be used to investigate how the rate of fermentation varies with temperature. [2] On the axes below, sketch the shape of the graph you would expect to obtain from the results of the experiment in b)(i). Rate (iii) Comment on the shape of your graph in b). Temperature [1] TOTAL (Continued...) /

15 TOPIC 15 Questionsheet 9 Continued FERMENTATION c) In Brazil, ethanol is made by fermentation and added to petrol on a large scale. The product is called gasohol. Explain why this is particularly beneficial to countries like Brazil, and identify the main economic and environmental benefits of this practice. d) State two advantages (other than economic ) of manufacturing industrial ethanol in the UK by the hydration of ethene rather than fermentation. TOTAL / 14

16 TOPIC 15 Questionsheet 10 SYNTHETIC ETHANOL PROCESS Industrial ethanol is manufactured in the UK by the hydration of ethene, a reversible gaseous phase reaction in which ethene and steam are compressed to a pressure of 70 atm and then passed over a catalyst, of phosphoric(v) acid absorbed on silica, maintained at a temperature of 300 C. a) (i) Write an equation for the hydration of ethene. What mechanistic type is the reaction? b) The reaction is believed to occur via an intermediate X, shown below. This reacts with a molecule of water to give protonated ethanol, Y, from which ethanol is formed by the loss of a proton. X + CH 3 CH 2 :OH 2 CH 3 CH 2 + OH 2 Y CH 3 CH 2 + O H H CH 3 CH 2 + H + O H (i) What type of reaction intermediate is X? One of the curly arrows in the above mechanism has been incorrectly printed. Draw a circle round it, and state what is wrong with it. c) Given that the hydration of ethene is exothermic, state one advantage and one disadvantage of conducting the process at a high temperature. Advantage... [1] Disadvantage... [1] TOTAL (Continued...) /

17 TOPIC 15 Questionsheet 10 Continued SYNTHETIC ETHANOL PROCESS d) (i) State and explain the main reason for operating the process at a high pressure.... [3] Give two economic disadvantages of high pressure processes. e) (i) Why is the catalyst absorbed on to silica? What effect (if any) does the catalyst have on the yield of ethanol at equilibrium? f) List the three essential stages that you would expect to be involved in turning the mixture of hot gases from the converter into industrial methylated spirits.... [3] TOTAL / 16

18 TOPIC 15 Questionsheet 11 ETHANOL AS A FUEL The use of ethanol as a fuel is being promoted on the grounds that, since it can be made by the fermentation of plant products, it is a renewable energy source. However, before petrol could be replaced by ethanol, its effect on the environment would have to be assessed. a) Write equations for the complete combustion of 1 mole of (i) octane, and ethanol. (i) Octane... [1] Ethanol... [1] b) Calculate the enthalpy change for the complete combustion of 1 dm 3 of (i) octane, and ethanol. (i) Octane (Density of octane = 0.72 g cm -3. H c (C 8 H 18 (l)) = kj mol -1 ) Ethanol (Density of ethanol = 0.79 g cm -3. H c (C 2 H 5 OH(l)) = kj mol -1 ) c) Calculate the mass of carbon dioxide produced by the complete combustion of (i) 1 dm 3 of octane, and 1dm 3 of ethanol. (i) 1 dm 3 of octane 1 dm 3 of ethanol d) Hence calculate the mass of carbon dioxide produced per kilojoule of energy for (i) octane, and ethanol. Comment on your results with regard to impact on the environment. (i) Octane... [1] Ethanol... [1] Comment... e) Why should ethanol made by fermentation be regarded as a greener fuel (i.e. one which is more friendly to the environment) than synthetic ethanol?... [3] TOTAL / 16

19 TOPIC 15 Questionsheet 12 DISPOSAL OF ORGANIC WASTE Household waste and much industrial waste is largely organic. Some can be recycled; otherwise it is generally tipped in landfill sites or incinerated. a) (i) Some plastics are recycled by melting them, but the process is difficult to operate economically. Why is this? How can two other types of organic waste material be recycled? b) State two disadvantages of disposing of waste in landfill sites. c) Incineration avoids the disadvantages of landfill sites and has the additional advantage that the process is exothermic. Give two ways in which the heat released could be put to good use. d) To avoid atmospheric pollution, incineration must be carried out at a sufficiently high temperature and with a plentiful supply of air. Explain the pollution problems stemming from (i) too low a temperature, and insufficient oxygen. (i) Too low a temperature Insufficient oxygen e) State and explain the environmental problem that can arise from the incineration of sulfur- and nitrogencontaining materials.... [3] f) Suggest how the fumes from an incinerator could be treated chemically so as to reduce noxious emissions. TOTAL / 17