A. Harman - moulsham high school 1

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1 A. arman - moulsham high school 1

2 a) Demonstrate understanding of the terms: (i) rate of reaction The amount in moles of a reactant which is used up in a given time (iii) rate equation as the form rate=k[a] x [B] y which shows how the rate of chemical reaction depends on the concentration of reactants (A & B) and the rate constant k. order of reaction is the power to which the concentration of a reactant is raised in the rate equation. Zero order indicates the reactant concentration does not affect the rate, rate [A] 0. First order indicates that the reactant concentration is directly proportional to the rate, rate [A] 1. Second order indicates that the square of the reactant concentration is directly proportional to the rate, rate [A] 2. (iv) rate constant is the proportionality constant k in a rate equation. (v) (vi) (vii) half-life life - t ½ is the time taken for the concentration of a reactant to fall to half its original value rate-determining step is the slowest step in the reaction activation energy the energy barrier that must be surmounted before reaction can occur (viii) catalyst increases the rate of a reaction but is not used up itself (xi) heterogeneous catalysis A catalyst that is present in a different phase to the reactants. Frequently reactants are in the gaseous phase with a solid catalyst. b) Plan an investigation for measuring extent of a reaction with time, and justify the procedures involved. c) Deduce from experimental data for simple zero, first and second order reactions only: half life order of reaction rate equation rate-determining step, related to possible reaction mechanisms activation energy (by graphical methods only; the Arrhenius equation will be given if needed) d) Predict the effects of concentration, temperature and catalysis c on the rate of reaction, and interpret them in terms of collision theory, the distribution of molecular kinetic energies, and alternative reaction pathways of lower activation energy (qualitative only); including links to topic 7. e) Evaluate information by extraction from text and the Book of Data about catalysis. A. arman - moulsham high school 2

3 1. (a) ydrogen iodide decomposes at high temperature to form hydrogen and iodine gases. Describe what you would observe as hydrogen iodide decomposes. (b) The rate determining step of this second order reaction is 2I(g) 2(g) + I 2(g) (i) Write the rate equation for the reaction. What are the units of the rate constant for this reaction, assuming that time is measured in seconds (s)? (c) The rate constant k was measured at different temperatures. In the table below the data have been converted into values of 1/temperature and ln k. 1/ temperature 1 /K ln k A. arman - moulsham high school 3

4 (i) Plot a graph of ln k, on the vertical axis, against 1/temperature, on the horizontal axis. (3) Measure the gradient of your graph. A. arman - moulsham high school 4

5 (iii) The gradient of your graph is related to the activation energy of the reaction, E A, by gradient = E A R where R = 8.31 J K 1 mol 1 Use this relationship to calculate the activation energy, E A, for the reaction. (iv) The presence of nichrome wire greatly increases the rate of decomposition of hydrogen iodide at high temperature. Suggest how the nichrome wire might be acting as a catalyst. (Total 12 marks) A. arman - moulsham high school 5

6 2. This question is about the kinetics of the reaction between 2-bromo-2-methylpropane and sodium hydroxide in a suitable solvent. (C 3 ) 3 CBr + NaO (C 3 ) 3 CO + NaBr Equal volumes of mol dm 3 solutions of the two reactants were mixed together and maintained at a constant temperature of 30 C. The concentration of hydroxide ions was determined at different times. The results are shown in the table below. [O ] /mol dm 3 Time /s (a) Describe how the concentration of hydroxide ions could be determined during the reaction (3) A. arman - moulsham high school 6

7 (b) (i) Plot a graph of hydroxide ion concentration (vertical axis) against time (horizontal axis) on the grid below. Mark on your graph TWO consecutive half-lives. Measure their values and write them below. First half-life... Second half-life... A. arman - moulsham high school 7

8 (iii) What is the order of the reaction? Explain how you used your half-lives to arrive at your answer (iv) Explain why your answer to (iii) is an overall order (v) Suggest a rate equation for this reaction. Rate = (c) (i) What mechanism is likely to be operating in this reaction? Justify your answer Write equations to show the steps involved in your chosen mechanism for this reaction. (Total 13 marks) A. arman - moulsham high school 8

9 3. (a) The distribution of the energy of particles in a gas at temperature T1 is shown below. (i) On the diagram above, draw the distribution of energy of particles at a lower temperature, T2. Use the diagram to explain why the rate of a reaction increases with an increase in temperature (3) A. arman - moulsham high school 9

10 (iii) Explain fully why a catalyst increases the rate of a reaction (b) The fermentation of glucose is an exothermic reaction and is catalysed by enzymes in yeast. The reaction is slow at room temperature. C 6 12 O 6 (aq) 2C 2 Η 5 ΟΗ(aq) + 2CO 2 (g) (i) Describe, with the aid of a diagram, an experiment you could do to follow the progress of this reaction at different temperatures (4) A. arman - moulsham high school 10

11 Would you expect S system to be positive or negative for this reaction? Justify your answer with TWO pieces of evidence (iii) Deduce the sign of S surroundings. Show your reasoning (Total 15 marks) 4. 2-bromo-2-methylpropane reacts with aqueous sodium hydroxide as shown in the equation below. (C 3 ) 3 CBr + NaO (C 3 ) 3 CO + NaBr A series of experiments was carried out to investigate the kinetics of this reaction. Initial concentration of (C 3 ) 3 CBr /mol dm 3 Initial concentration of NaO /mol dm 3 Initial rate of reaction /mol dm 3 s A. arman - moulsham high school 11

12 (a) (i) Give the order of the reaction with respect to 2-bromo-2-methylpropane... sodium hydroxide... Write the rate equation for this reaction.. (b) Use one set of the data to calculate the rate constant for this reaction. Include the unit of the rate constant in your answer. (c) The slowest step of the mechanism is the following reaction (C 3 ) 3 CBr (C 3 ) 3 C + +Br your answer. Is your rate equation consistent with this information? Explain (d) In another series of experiments, the rate of the reaction was measured at different temperatures. Complete the missing numbers in the table below. temperature (T) /K 1/temperature (1/T) /K 1 rate /mol dm 3 s 1 ln(rate) A. arman - moulsham high school 12

13 (e) On the axes below plot a graph of ln(rate) on the vertical axis against 1/T on the horizontal axis. (f) Use the Arrhenius equation ln(rate) = constant E A (1/T) R to calculate the value of the activation energy, E A, for the reaction. [R = 8.31 J K 1 mol 1 ]. Show your working clearly and give your answer to 2 significant figures. (Total 12 marks) A. arman - moulsham high school 13

14 5. But-1-ene, C 2 ==CC 2 C 3, can be converted into a polymer. (a) Draw the structure of part of the polymer, showing TWO repeating units. (b) The polymerisation of C 2 ==CC 2 C 3 is exothermic and involves the use of a catalyst. The diagram below shows the energy profile for this polymerisation using a catalyst. Indicate on the profile the activation energy for the catalysed process. Add another energy profile to the diagram for the polymerisation where a catalyst is not used. (3) (c) Explain, in terms of activation energy and the collision theory, why the rate of polymerisation is greater when (i) a catalyst is used A. arman - moulsham high school 14

15 heat energy is provided to start the process (Total 7 marks) 6. This question is about the kinetics of the reaction in which ammonium cyanate, N 4 CNO, turns into urea, N 2 CON 2, in aqueous solution. N 4 CNO(aq) ΝΗ 2 CON 2 (aq) The table below shows the mass of urea, m t, which formed at different times in a solution of ammonium cyanate of known starting concentration. When the reaction stopped the mass of urea, m final, was 20.3 g. Time / min Mass of urea, m t /g m final m t /g (a) Complete the final column of the table. A. arman - moulsham high school 15

16 (b) Plot a graph of m final m t (on the vertical axis) against time (on the horizontal axis). (c) The graph can be used to work out a rate equation for the reaction. What term in the rate equation for the reaction is proportional to m final m t?... (d) (i) Show TREE successive half-life measurements on your graph, and give their values A. arman - moulsham high school 16

17 Use the half-lives to decide whether the reaction is zero order, first order or second order. Explain how you decided the order. Order of reaction... Explanation... (iii) Suggest a possible rate equation for the reaction. (e) A student thought that water might take part in the rate-determining step of the reaction. (i) What is meant by the rate-determining step? The solution of ammonium cyanate used in the experiment initially contained 0.35 moles of ammonium cyanate in approximately 1 dm 3 (55.5 moles) of water. Is the order you calculated in (d) an order with respect to ammonium cyanate, or could it include the water as well? Explain your answer. (Total 12 marks) 7.(a) The equation for the reaction between thiosulphate ions and hydrogen ions is 2 + S2 O3 (aq) + 2 (aq) SO2(g) + S(s) + 2O(l) (i) What is the oxidation number of sulphur in thiosulphate ions, 2 S 2O 3.. sulphur dioxide, SO 2 sulphur, S?.... A. arman - moulsham high school 17

18 State and explain the type of redox reaction represented by the equation. Type of reaction Explanation (b) The effect of temperature on the rate of this reaction was investigated. Solutions of sodium thiosulphate and hydrochloric acid were heated to the same temperature. The time for the reaction to produce a fixed amount of sulphur was measured, and the reaction repeated at different temperatures. (i) ow could you heat the solutions to ensure that both reactants are at the same temperature? ow could you measure the time for the reaction to produce a fixed amount of sulphur? (iii)... ow could you obtain a measure of the rate of reaction from your measurement of time? A. arman - moulsham high school 18

19 (c) The results obtained from a series of experiments are tabulated below. Most of the measurements have been converted into values of 1/temperature and ln rate. temperature/k 1/temperature/K 1 rate ln rate (i) Complete the table by calculating the missing values. Plot a graph of ln rate on the vertical axis, against 1/temperature on the horizontal axis. (3) A. arman - moulsham high school 19

20 (iii) Calculate the activation energy, E A, for the reaction, using your graph and the relationship: E ln rate = constant A (1 T ) R where R = 8.31 J K 1 mol 1. Remember to include a sign and units in your answer. (3) (Total 16 marks) 8. This question is about the hydrolysis of 2-bromo-2-methylbutane. C 5 11 Br + 2 O C 5 11 O + Br (a) 15 cm 3 of water was mixed with 15 cm 3 of ethanol. 1.0 cm 3 of 2-bromo-2-methylbutane was added to this mixture. The conductivity of this mixture was measured and rose from 0 to 200 microsiemens in 600 s. The experiment was repeated using equal volumes of water and ethanol, with 2.0 cm 3 of 2-bromo-2-methylbutane in the 31 cm 3 of mixture. The conductivity of the mixture rose from 0 to 400 microsiemens in 600 s. (i) Explain why the conductivity of the mixture increases during these reactions. Why was an ethanol/water mixture used for this reaction rather than water on its own? (iii) What is the effect on the rate of the reaction of doubling the concentration of 2-bromo-2-methylbutane? (iv) Deduce the order of the reaction with respect to 2-bromo-2-methylbutane. A. arman - moulsham high school 20

21 (v) Explain why this is the order of reaction with respect to 2-bromo-2-methylbutane and not the overall order of the reaction. (b) The table below shows the results from another experiment where a solution of 2-bromo-2-methylbutane is reacted with varying concentrations of hydroxide ions. A few drops of an acid-alkali indicator are added to the mixture and the time for the indicator to change to the acidic colour is measured. [C 5 11 Br] /10 2 mol dm 3 [O ] /10 3 mol dm 3 Time /s (i) Calculate the rate of the reaction, in mol dm 3 s 1, for each concentration of hydroxide ions. What effect does doubling the concentration of hydroxide ions have on the rate of the reaction? (iii) What is the order of the reaction with respect to the hydroxide ions? A. arman - moulsham high school 21

22 (c) When 2-bromo-2-methylbutane reacts with water, or hydroxide ions, the mechanism for the reaction is the same. (i) Use your answers to (a)(iv) and (b)(iii) to write the rate equation for the reaction with hydroxide ions. Rate = Write a mechanism for the reaction which is consistent with your rate equation. (Total 12 marks) 9. ydrogen peroxide decomposes to form water and oxygen. 2 O 2 (aq) 2 O(l) + 21 O 2 (g) (a) Suggest a method for following the rate of this reaction A. arman - moulsham high school 22

23 (b) The reaction is first order with respect to hydrogen peroxide. (i) Explain what is meant by the term first order..... The overall order of the reaction is one. Give the rate equation for the reaction. Rate = (iii) ow would you use a graph of hydrogen peroxide concentration against time to show that the reaction is first order? (c) The data in the table show the effect of temperature on the rate of this reaction. T /K Rate 1/T / mol dm 3 s 1 /K 1 ln(rate) A. arman - moulsham high school 23

24 (i) On the axes below, sketch graphs for two temperatures, T 1 and T 2, where T 2 is greater than T 1, and use them to explain why increasing temperature has a dramatic effect on the rate of this reaction (4) A. arman - moulsham high school 24

25 Plot a graph of ln(rate), on the vertical axis, against 1/temperature, on the horizontal axis, on the grid below. (3) A. arman - moulsham high school 25

26 (iii) Use your graph and the equation below to calculate the activation energy, E A, for this reaction. ln(rate) = constant E A R (1/T) where R = 8.31 J K 1 mol 1 You should include the sign and units with your answer which should be given to two significant figures. (3) (Total 16 marks) 10. The hydration of propanal, C 3 C 2 CO, is an exothermic reaction. C 3 C 2 CO(l) + 2 O(l) C 3 C 2 C(O) 2 (aq) The kinetics of this reaction can be followed by measuring the temperature of the reaction mixture when propanal is added to an excess of water. (a) Suggest how you would carry out a practical investigation of the kinetics of this reaction (3) A. arman - moulsham high school 26

27 (b) Results of an investigation of this reaction are shown in the table below. time, t /s temperature, T t /ºC (T final Tt) /ºC final 95 0 (i) Water is present in excess. What is the significance of the value of (T final T t )?... A. arman - moulsham high school 27

28 Plot a graph of (T final T t ) on the vertical axis against time on the horizontal axis. (3) (iii) By taking appropriate readings from your graph show that the reaction is first order with respect to propanal. Explain your reasoning (3) A. arman - moulsham high school 28

29 (iv) The reaction is zero order with respect to water. Write the overall rate equation for the reaction. (Total 11 marks) 11. (a) Equimolar amounts of 1 chlorobutane and sodium hydroxide in solution were mixed at 29 C and the concentration of hydroxide ions was determined at various times. The following results were obtained. Time /min [O ] /mol dm A. arman - moulsham high school 29

30 (i) Plot a graph of the concentration of hydroxide ion on the vertical axis against time on the horizontal axis. (3) Find TWO successive values for the half life. First half life... Second half life... (iii) What is the order of the reaction? Give a reason for your answer. Order... Reason... (iv) Why is your answer to (iii) the overall order for this reaction? A. arman - moulsham high school 30

31 (v) Suggest an equation for the rate determining step of the reaction between 1 chlorobutane and sodium hydroxide which is consistent with your answer to (iv). (b) When 1 chlorobutane is heated with a concentrated solution of potassium hydroxide in ethanol, a different reaction takes place. A gas is produced as the organic product. Give the name and structural formula of this gas. Name Structural formula (Total 11 marks) 12. The decomposition of dinitrogen pentoxide, N 2 O 5, has been studied in solution. When tetrachloromethane is used as a solvent, one product (nitrogen dioxide) is retained in solution, while oxygen gas is given off as the other product. The equation for the overall process is: N O (CCl ) 1 2NO (CCl ) + O (g) (a) Draw a diagram of the apparatus you would use to follow the rate of this reaction. (2 marks A. arman - moulsham high school 31

32 (b) The rate equation for the reaction is rate = k [N 2 O 5 ] A suggested mechanism for the reaction is 1st step N O NO + NO nd step NO + NO NO + O + NO th step NO + NO 2NO 3 2 (i) What is the order of reaction with respect to N 2 O 5? What are the units of the rate constant k? (iii) Suggest which is the rate determining step. Explain your reasoning. Rate determining step... Explanation... (c) The rate constant k was measured at different temperatures. (i) Suggest a practical method for maintaining the temperature constant during each measurement. A. arman - moulsham high school 32

33 The table below shows data for temperature and rate constant. Most of the data have been converted into values of 1/temperature and ln k. Complete the table by calculating the missing values. temperature /K 1/ temperature 1 /K k ln k (iii) Plot a graph of ln k on the vertical axis against 1/temperature, on the horizontal axis. (3) A. arman - moulsham high school 33

34 (iv) The relationship between rate constant, k, and temperature is given by the equation: ln k = C EA R (1/T) where T is the temperature in kelvin, E A is the activation energy in J mol 1, C and R are constants, R = 8.31 JK 1 mol 1. (You do not need to know or find the value of C.) Use your graph from (iii) to calculate the activation energy, E A for the reaction. (3) (Total 15 marks) A. arman - moulsham high school 34

35 a) Recall the characteristic behaviour of arenes (benzene, as a typical example), limited to: (i) Combustion Burn with fairly sooty flame due to high carbon to hydrogen ratio. Treatment with: Bromine Electrophilic substitution In the prescence of a halogen carrier eg. Anhydrous FeBr 3 bromine can be substituted onto the ring. The carrier allows the production of Br δ +---Br δ ----FeBr 3 which is a good electrophile. Br + Br 2 Anhydrous FeBr 3 Concentrated nitric and sulphuric acid Nitration - Electrophilic substitution Produces the nitrated species. The conc 2So4 helps generate the attacking species NO 2 +. NO 3 + 2SO 4 2NO SO 4-2NO 3 + NO O NO 2 2 SO 4 + NO O Nitrobenzene Concentrated sulphuric acid Sulphonation Electrophilic substitution. The electrophile is thought to be SO 3 (sulphur trioxide) SO SO 4 (iii) Alkylation by the Friedel Crafts reaction Electrophilic substitution RCl in the prescence of aluminium chloride, will form a complex, R+AlCl4-, in which R+ acts as an electrphile. RCl + AlCl 3 R + AlCl 4 - R + + AlCl 3 + Cl R A. arman - moulsham high school 35

36 (iv) Addition reactions with hydrogen and with chlorine Severe conitions needed Ni Cyclohexane + 3Cl 2 hυ Cl Cl Cl Cl Cl Cl b) Recall the typical behaviour of phenols limited to: (i) Combustion Solubility in water and the acidic nature of the mixture Like other alcohols phenol interacts with water forming hydrogen bonds. Due to the arene ring solubility is not high. p in water is weakly acidic ( 6) (iii) Treatment with: Sodium Metal + acid A salt + water. Phenol is acidic enough to react. It forms the phenoxide salt and hydrogen gas. Na + C 6 5O C 6 5O - Na + + ½ 2 Aqueous sodium hydroxide Acid +Alkali A salt + water. Alcohols are not acidic enough to react with soudium hydroxide but phenol reacts to give the phenoxide salt and water. C 6 5O + NaO C 6 5O - Na + + 2O (iv) Aqueous sodium carbonate No reaction. Phenol is not a strong enough acid to react with the weak base sodium carbonate Ester formation Phenol is not reactive enough to form esters with carboxylic acids, it must react with an acyl chloride or an acid anhydride. The lone pair of electrons on the O of Phenol becomes delocalised into the ring and makes the phenol O less reactive. O O 2 C 3 Catalyst + (C 3 CO) 2 O + C 3 CO 2 (v) Comparative reactivity of the ring system with bromine and with nitric acid The delocalisation of the O lone pair into the ring makes the electron density on the ring even greater, making the ring even more attarctive to electrophiles. The reactions occur so rapidly that multiple substitutions are likely. A. arman - moulsham high school 36

37 c) Interpret the reactions of arenes and phenols in terms of the processes of bond-breaking breaking and bond- making by electrophilic or nucleophilic attack and by reference, as appropriate, to electron pair p availability, bond polarisation, bond energy, and the structure and bonding of the benzene ring, including links to topic 8 and 10. d) Evaluate information by extraction from text and the Nuffield Book of data about arenes and phenols (examined in the synoptic paper only). 13. Three reactions of methylbenzene can be summarised on a flow sheet. C 3 C 3 C B + C Br /FeBr 2 3 NO A 2 fuming sulphuric acid 3 Br A. arman - moulsham high school 37

38 (a) Name substance A and the reagents B and C. A. B. C. (b) (i) Draw the structural formula for 4 methylbenzenesulphonic acid. State the formula of the molecule which attacks the benzene ring in reaction 3. (3) (iii) Name an important group of industrial products that is made from benzenesulphonic acids. (c) (i) Write an equation to show how the catalyst iron(iii) bromide induces polarization of a bromine molecule in reaction 2. Classify reaction 2 as fully as possible. (d) A student tried to make 4 methylcyclohexanol by the following route. C 3 C 3 C 3 Step 1 Step 2 Br Br O (i) Suggest reagents and conditions for each step. Step 1 Reagent. Conditions Step 2 Reagent. Conditions (4) A. arman - moulsham high school 38

39 The final yield of 4 methylcyclohexanol was rather low. This was thought to be due to the formation of some 4 methylcyclohexene. Suggest a chemical test and the colour change you would expect to observe for an alkene such as 4 methylcyclohexene. Reagent:. Colour change: from to. (Total 15 marks) 14. This question is about the reactions of benzene and some related compounds. (a) (i) Name the reagent and conditions for Reaction 1. Reagent... Conditions... Give the formula of the attacking species in this reaction.... A. arman - moulsham high school 39

40 (b) (i) Give the structural formula of the organic compound A formed in Reaction 2. State the type of reaction and its mechanism in Reaction 2. Type... Mechanism... (iii) Phenol, C 6 5 O, will react with bromine in a similar way to benzene, but no catalyst is needed. Explain why phenol will react readily with bromine without a catalyst (c) (i) Give the name of product B.... Explain how aluminium chloride acts as a catalyst in Reaction 3. You may find it helpful to use an equation in your answer (d) (i) What condition is needed for chlorine to react with benzene in Reaction 4?... Give the systematic name of the product of Reaction A. arman - moulsham high school 40

41 (e) (i) Suggest a raw material from which benzene can be produced.... Suggest a reason why the use of benzene in school laboratories is illegal.... (Total 15 marks) 15. This question is about the reactions of methoxybenzene, which are summarised in the following diagram. (a) Draw the fully displayed formula for methoxybenzene. A. arman - moulsham high school 41

42 (b) Three of the reactions in the diagram are electrophilic substitution reactions. Explain what is meant by the term electrophilic substitution (c) Draw the structural formula for 2-nitromethoxybenzene formed when methoxybenzene reacts with nitric acid. (d) Give the molecular formulae of two of the products, A and B, formed when methoxybenzene reacts with bromine in an inert solvent. A B (e) (i) Suggest the name for the organic product, C, formed when methoxybenzene reacts with concentrated sulphuric acid... Suggest ONE use for the class of chemicals to which C belongs... (f) (i) Name reactant D and catalyst E needed to make methoxycyclohexane from methoxybenzene. D... E... A. arman - moulsham high school 42

43 This reaction is not a substitution reaction. Give TWO alternative names which do describe this type of reaction... (g) Many arenes like methoxybenzene are made from benzene. (i) What is the natural resource from which benzene is produced?. Suggest why methoxybenzene rather than benzene is used in schools and colleges.. (Total 14 marks) 16. Some of the reactions of phenol are summarised in the following diagram. (a) (i) Give TWO observations you would make when sodium reacts with molten phenol in Reaction 1. A. arman - moulsham high school 43

44 Give the name and the molecular formula for the organic product, A, formed in Reaction 1. Name... Molecular formula (b) (i) Draw the fully displayed formula for the organic product, B, formed in Reaction 2. What new functional group is in compound B and is not in phenol? (iii) Suggest a use for chemicals such as compound B. (c) (i) Name the chemical C used to make 2,4,6-trinitrophenol from phenol in Reaction 3. Draw the structural formula for 2,4,6-trinitrophenol. (d) (i) Name substance D, formed when phenol reacts with bromine water in Reaction 4. Suggest a use for halogenated phenol compounds. (e) Two of the reactions in the diagram are electrophilic substitution reactions. A. arman - moulsham high school 44

45 Give the formula of the attacking electrophile for each reaction (f) A solution of phenol in water is more acidic than a solution of ethanol in water. Explain why phenol is more acidic than ethanol (Total 15 marks) 17. The reaction of 2 hydroxybenzoic acid with ethanoic anhydride can be described as a nucleophilic substitution. (i) Draw the displayed formula of ethanoic anhydride. Suggest why ethanoic anhydride reacts more readily than ethanoic acid with the phenolic group. (Total 4 marks) A. arman - moulsham high school 45

46 18. Aspirin may be reacted with dilute aqueous sodium hydroxide to modify its structure before being used as a drug. (i) Give the structural formula of the compound which forms when aspirin is reacted with dilute aqueous sodium hydroxide at room temperature. Suggest TWO advantages of using the compound in (i) as a drug instead of aspirin. (Total 3 marks) 19. Read the passage on BENZENE straight through, and then more carefully, in order to answer the following questions. (a) (i) Draw the displayed formula for benzene (iii) Write a balanced equation for the dehydrogenation of cyclohexane, C 6 12, to benzene, C 6 6. Suggest ONE reason why platforming might be preferred to using aluminium oxide (b) Classify the following reactions as substitution, elimination or addition reactions. (i) The reaction between benzene and chlorine to form 1,2,3,4,5,6 hexachlorocyclohexane The reaction between benzene and chlorethene to form ethylbenzene (c) Name the chemical used to produce dodecylbenzenesulphonic acid from dodecylbenzene. A. arman - moulsham high school 46

47 (d) Write a summary in continuous prose, in no more than 100 words, describing the production of benzene from petroleum. You are NOT asked to summarise the whole passage, nor to include equations in your summary. At the end of your summary state the number of words you have used. (9) Credit will be given for answers written in good English, using complete sentences and with correct use of technical words. Avoid copying long sections from the original text. Numbers count as one word, as do standard abbreviations and hyphenated words. Any title you give to your passage does not count in your word total. There are penalties for use of words in excess of 100. (Total 15 marks) BENZENE Benzene was first discovered by Michael Faraday in London in By this time gas lighting was becoming common in London. The Portable Gas Company was producing gas by heating whale oil in a furnace. When they compressed the gas to put it in cylinders an oily liquid separated out. They told Faraday about this and he set about identifying the liquid. e distilled it and collected a fraction which boiled at 80 C and condensed to a clear liquid. We now know this as benzene. In 1834 Mitscherlich discovered that the same colourless liquid could be obtained by heating benzoic acid with lime. In 1845 ofmann demonstrated the presence of benzene in coal naphtha, the lowest boiling fraction obtained by the distillation of coal tar, and in 1848 Mansfield succeeded in isolating benzene from coal naphtha. Now most benzene is produced from petroleum. Petroleum is fractionally distilled to separate the crude oil into fractions on the basis of their boiling points. A typical crude oil composition is 2% butane, 11% petrol, 14% naphtha, 17% furnace oil, 39% gas oil and 17% residue. The naphtha fraction which contains hexane is used to produce benzene. The naphtha fraction is purified to remove sulphur compounds which would poison the catalyst used in the process. Sulphur compounds are removed by reduction to form hydrogen sulphide. This is known as hydrodesulphurisation (DS) and leaves a very low concentration of sulphur in naphtha. The hydrogen sulphide produced is used to manufacture sulphur and sulphuric acid. This treatment was originally only used in the production of sulphur free fuels but it is now used to reduce the sulphur content of most crude oil fractions. Purified naphtha is now heated to about 770 K. It then passes into a reactor where one of two processes may be used, depending on the catalyst. An aluminium oxide catalyst may be used with the reactants at a pressure of 40 atmospheres. exane first reacts to form cyclohexane and hydrogen. Then cyclohexane is dehydrogenated to form benzene. Other aromatics like methylbenzene and dimethylbenzenes are also produced. The mixture of products is dissolved in a suitable solvent. The aromatic products are separated from the solvent by further distillation in fractionating towers. Residual impurities are removed, for example, by passing through an active clay catalyst. A final fractionation is then used to separate and purify benzene. A. arman - moulsham high school 47

48 The second process is called platforming because it uses the metal platinum. In platforming the same chemical reactions are involved. The difference is that a platinum catalyst is used, in spite of the extra expense, and a lower pressure of 15 atmospheres is sufficient. Benzene is the starting material for a large number of useful chemicals and materials. The insecticide BC, benzenehexachloride (systematic name, 1,2,3,4,5,6 hexachlorocyclohexane) is made by passing chlorine through benzene irradiated by ultra violet light. BC is particularly valuable in the fight against the locust. Benzene is the starting material for the manufacture of many plastics. By reacting benzene with chloroethane in the presence of an aluminium chloride catalyst at 80 C, ethylbenzene is formed. This is dehydrogenated by heating to 600 C with a zinc oxide catalyst to produce phenylethene (styrene) which polymerizes to form polystyrene. Benzene is also the starting material for making many soapless detergents. Benzene reacts with dodec l ene in the presence of a suitable catalyst to produce dodecylbenzene. (C ) C C The dodecylbenzene is then sulphonated to produce dodecylbenzenesulphonic acid which can then be neutralized to produce sodium dodecylbenzenesulphonate, a biodegradable soapless detergent. So it can be seen that from Faraday's discovery a vast and vital range of chemicals has developed. (590 words) ~ A. arman - moulsham high school 48

49 a) Demonstrate understanding of the nomenclature and corresponding displayed and structural formulae for carbonyl compounds, carboxylic acids, esters and acid chlorides. C O Aldehyde ( ending - al ) C O O Carboxylic acid ( ending - oic ) C O C C Ketone ( ending - one ) C O O C Esters C O Cl Acyl Chloride ( ending - oyl chloride ) C O N Amide b) Recall the typical behaviour of aldehydes and ketones limited to: (i) Combustion Miscibility with water Aldehydes and ketones mix with water if they are small but not if the carbon chain is long. They form hydrogen bonds to water and themselves. (iii) Production from alcohols by oxidation 1 o alcohols are oxidised to aldehydes and then to carboxylic acids by excess sodium or potassium dichromate (or potassium permanganate)and sulphuric acid. Partial oxidation is achieved by adding a small amount of oxidising agent. 2 o alcohols are oxidised to ketones by using the same conditions. (iv) Oxidation of aldehydes to carboxylic acids The dichromate ion and other mild oxidising agents convert aldehydes to carboxylic acids. 3C 3C 2CO + Cr 2O C 3C 2CO O + 2Cr 3+ (v) Results of testing t with Benedict s solution The Benedict s solution oxidises aldehydes to carboxylic acids but not ketones. The Cu(II) ions in Benedict s are reduced to Cu(I)ions resulting in a brick red precipitate (vi) Reaction with Brady s reagent Nucleophilic addition to the C=O but this is immediately followed by an elimination reaction to give an orangey coloured crystalline solid (a 2,4-dinitrophenyhydrazone). c) Recall the typical behaviour of carboxylic acids limited to: (i) Solubility in water Acids will mix with water by hydrogen bonding. The smaller the acid s carbon chain the more soluble it is. Acidity and formation of salts Carboxylic acids weak acids but are acidic enough to react with the strong base sodium hydroxide and the weak base sodium carbonate. Both A. arman - moulsham high school 49

50 reactions make a sodium salt (RCO 2 -Na + ). (iii) (iv) Reaction with alcohols to form esters The alcohol acts as a nucleophile as it has a lone pair on its oxygen. The reaction requires either an acid catalyst (eg. Conc. sulphuric acid). The linking oxygen (C-O-C) comes from the alcohol and not the acid. The acid loses the O group and not the alcohol. Naming esters:- first half of name comes from the alcohol and the second half comes from the carboxylic acid eg. Methyl benzoate comes from methanol and benzoic acid. Relationship to alcohols, aldehydes and ketones d) Recall the typical behaviour of esters and acyl chlorides limited to hydrolysis by water Esters react slowly with water but may be hydrolysed by refluxing with either an acid or an alkali. Refluxing with an acid simply reverses the preparation of the ester. The acid catalyses the reaction. The reaction is an equilibrium; hence there are always molecules of both reactants and products present after the reaction. R O C O C R' O + R O C O + RC 2 O When an ester is refluxed with an alkali such as aqueous sodium hydroxide, it is fully hydrolysed to the alcohol and the sodium salt of the acid. Subsequent acidification produces the acid. Acyl chlorides react with water by the water molecule donating a lone pair of electrons to the carbon atom of the acyl group. The resulting molecules formed are the carboxylic acid and hydrogen chloride gas. O O R C + 2 O R C + Cl Cl O e) Interpret the reactions of carboxylic acids, aldehydes and ketones, in terms of nucleophilic or electrophilic attack, including the relative electron attracting power of the different group in acids and their derivatives, oxidation and reduction. f) Interpret the infra-red red spectra of acids and carbonyl compounds, including the effect of hydrogen bonding - ydrogen bonding broadens the absorption bands on the spectrum. g) Evaluate information by extraction from text and Nuffield Book of data about the properties of carboxylic acids and carbonyl compounds (examined in the synoptic paper only). A. arman - moulsham high school 50

51 20. This question is about 2 hydroxybenzoic acid and some of its reactions. ethanol an ester, A CO 2 O LiAl 4 C O 2 O B 2 hydroxybenzoic acid ethanoic anhydride CO 2 OCOC 3 Aspirin (a) ow would you show that 2 hydroxybenzoic acid contains a phenolic O group? Test... Result (b) When 2 hydroxybenzoic acid is reacted with ethanol under suitable conditions it forms an ester, A. Write a balanced equation for the reaction which occurs. A. arman - moulsham high school 51

52 (c) In the formation of compound B (i) what is the attacking ion derived from LiA1 4? explain why the 2 hydroxybenzoic acid molecule is susceptible to attack by this ion. (d) The reaction of 2 hydroxybenzoic acid with ethanoic anhydride can be described as a nucleophilic substitution. (i) Draw the displayed formula of ethanoic anhydride. Suggest why ethanoic anhydride reacts more readily than ethanoic acid with the phenolic group. (e) Aspirin may be reacted with dilute aqueous sodium hydroxide to modify its structure before being used as a drug. (i) Give the structural formula of the compound which forms when aspirin is reacted with dilute aqueous sodium hydroxide at room temperature. A. arman - moulsham high school 52

53 Suggest TWO advantages of using the compound in (e)(i) as a drug instead of aspirin. (Total 13 marks) 21.(a) The formula for aspirin is given below O C O O O C C 3 Name and describe the three types of intermolecular force between aspirin molecules. (5) (b) When aspirin is hydrolysed in sodium hydroxide solution, sodium 2 hydroxybenzoate is one of the products. (i) Name the other organic product of the reaction. Suggest a reason why aspirin may sometimes taste like vinegar. (c) A solution of sodium 2 hydroxybenzoate is added to some copper(ii) sulphate solution. A dark green solution forms. (d) State the type of reaction that occurs. Discuss the advantages and disadvantages of using aspirin as a medicine. (Total 10 marks) A. arman - moulsham high school 53

54 22. Ethanoic acid and ethanol react together to form ethyl ethanoate, C 3 CO 2 C 2 5, and water. (a) Draw a displayed formula of ethyl ethanoate. (b) Name the family of compounds to which ethyl ethanoate belongs.... (c) Write a balanced equation with state symbols for the reaction.... (d) An equilibrium was reached when the reaction was carried out using the amounts of substances shown in the table below. (i) Complete the table below to show the amounts of each substance present at equilibriuim. Number of moles in the reaction mixture Ethanoic acid Ethanol Ethyl ethanoate Water At the start of the experiment At equilibrium 0.2 Write an expression for the equilibrium constant, K c for the reaction, including all appropriate symbols. A. arman - moulsham high school 54

55 (iii) Use your expression to calculate the numerical value of K c (iv) Explain why K c for this reaction has no units. (e) (i) The reaction between ethanoic acid and ethanol is exothermic. What is the effect of an increase in temperature on the yield of ethyl ethanoate at equilibrium? Explain your answer. The reaction is catalysed by hydrogen ions. What is the effect of the presence of hydrogen ions on the yield of ethyl ethanoate at equilibrium? Explain your answer. (Total 15 marks) 23. (i) What organic compound reacts with methanoic acid to form an ester of molecular formula C 3 6 O 2? A. arman - moulsham high school 55

56 Name and draw the displayed formula of another ester which has the same molecular formula, C 3 6 O 2. Name... Displayed formula (3) (Total 4 marks) 24. What is the name of the compound represented by the following displayed formula C C C C O Ethanedioic acid is the simplest dicarboxylic acid. CO 2 CO Ethanedioic acid It is poisonous and occurs naturally in rhubarb leaves and sorrel. 2 (a) When ethanedioic acid reacts with sodium hydroxide TWO salts can form. (i) Draw the displayed formulae of both salts. Suggest how you could make sure that only ONE of the salts was formed in a preparation. A. arman - moulsham high school 56

57 (b) The ester dimethyl ethanedioate can be readily produced by refluxing ethanedioic acid with two other chemicals. Name these chemicals (Total 5 marks) 26. In the preparation of cyclohexanone (molar mass = 98 g mol 1 ) from cyclohexanol (molar mass = 100 g mol 1 ), 2.0 g of cyclohexanol was reacted and 1.2 g of cyclohexanone was obtained. Calculate the percentage yield, quoting your answer to 2 significant figures. A. arman - moulsham high school 57

58 27. The six structures, A to F, represent compounds with the same molecular formula, C 6 12 O. C C C C C C 3 O C C C 3 C C 2 5 O A B O C C C C C C O C D C C C O C C C C O C C C C C 3 E F (a) What is the name given to compounds which have different structural formulae but the same molecular formula?. (b) Which two of the compounds, A to F, are the same?. (c) What is the name of compound E?. (d) (i) Which of the compounds, A to F, could be readily oxidized to a carboxylic acid containing six carbon atoms?... Which TWO reagents would be used and what conditions are required? Reagents... Conditions. (3) (Total 9 marks) A. arman - moulsham high school 58

59 28. (a) (i) Propanone, C 3 COC 3, is a polar liquid. Draw a structural formula for propanone and use the symbols δ + and δ to identify the polar atoms in your formula. What simple experiment could you carry out to show that propanone is polar? You may find it helpful to draw a diagram. (iii) Explain why butanone, C 3 C 2 COC 3, has a higher boiling point (79 ºC) than propanone (56 ºC) (iv) Would you expect the boiling point of propanal, C 3 C 2 CO, to differ from that of propanone? Justify your answer (Total 7 marks) A. arman - moulsham high school 59

60 29. Ethanedioic acid is found in rhubarb leaves. O O C C O O Ethanedioic acid It is soluble in water and extremely poisonous. There are two end points when it is titrated with sodium hydroxide. (a) (b) Explain why ethanedioic acid is soluble in water by considering relevant intermolecular forces. Draw an appropriate diagram and mark the intermolecular bond angle. Suggest a reason why there are two end points when ethanedioic acid is titrated with sodium hydroxide. (4) (c) When ethanedioic acid is strongly heated, it decomposes to form carbon dioxide, water and another product. Write a balanced equation for this decomposition. (Total 8 marks) 30. This question is about phenol and benzoic acid, which are acidic, and benzaldehyde, which is neutral. Ka = mol dm 3 Ka = mol dm 3 (a) Which is the stronger acid, phenol or benzoic acid? Justify your choice A. arman - moulsham high school 60

61 (b) Suggest chemical tests, with results, which would distinguish each of these compounds from the others (5) (c) Benzoic acid can be distinguished from benzaldehyde by examining infra-red spectra. Suggest how the infra-red spectra of these compounds could be used to distinguish between them. You are not expected to give actual absorption values, but you should indicate the bonds in the molecules which would give rise to the distinguishing absorptions. Benzoic acid Benzaldehyde (iii) Calculate the p of a mol dm 3 solution of benzoic acid in water. You should make the usual two simplifying assumptions. (3) (e) Under suitable conditions phenol reacts with benzoic anhydride, (C 6 5 CO) 2 O, to form an ester. (i) What are the conditions?.. Give the name and structural formula for this ester. Name... A. arman - moulsham high school 61

62 Structural formula (f) Esters are often used in perfumes. Suggest TWO properties, apart from smell, which need to be considered for an ester to be suitable for use in a perfume A. arman - moulsham high school 62

63 31. This question is about propanal, C 3 C 2 CO, propanone, C 3 COC 3, and propanoic acid, C 3 C 2 CO 2. (a) Explain why all three compounds are soluble in water (b) Propanal and propanone contain the carbonyl group. State a chemical test for the presence of this group. Give the result of a positive test. Test. Result... (c) Propanal can be distinguished from propanone by its oxidation to propanoic acid. (i) Name an oxidising agent you would use State the colour change you would observe during the oxidation. From... to... (iii) State how propanone can be distinguished from propanal using infra-red spectra. You are not expected to give actual absorption values, but you should indicate the bonds in the molecules which would give rise to the distinguishing absorptions (d) A useful test for carboxylic acids is that they will neutralise sodium carbonate solution. Write a balanced equation, including state symbols, for the neutralisation of sodium carbonate solution by propanoic acid. A. arman - moulsham high school 63

64 (e) Give the names of TWO other inorganic chemicals that could be used to make sodium propanoate from propanoic acid (Total 10 marks) 32. This question is about the chemistry of benzoic acid, C 6 5 CO 2. The scheme below shows some reactions of benzoic acid. (a) (i) What type of reaction is Reaction 1? Suggest a reagent which could be used to convert the CO 2 group to the C 2 O group without affecting the benzene ring. (iii) Suggest why the reactant you chose in does not attack the benzene ring. A. arman - moulsham high school 64

65 (b) (i) Suggest a structural formula for A. Name the type and mechanism of this reaction. Type... Mechanism... (c) (i) Give the structural formula and state the name for B. Name... Give ONE use for the class of compounds to which B belongs. (d) (i) Give the name for C 6 5 COCl. C 6 5 COCl reacts more readily than benzoic acid with ethanol, also forming B as the product. Explain this difference in reactivity. A. arman - moulsham high school 65

66 (e) ydrogen can add to the benzene ring in benzoic acid, but only under conditions of high temperature and pressure in the presence of a catalyst. Explain why these severe conditions are necessary for this addition reaction to occur (Total 14 marks) 33. Two compounds, X and Y, are isomers with the formula C 4 8 O. They can be prepared from different alcohols, each containing four carbon atoms. Both compounds produce a yellow precipitate with Brady s reagent (2,4- dinitrophenylhydrazine). When the compounds are warmed with Benedict s solution, X forms a red-brown precipitate but Y does not change. When X is oxidised it produces C 3 C 2 C 2 CO 2. (a) Draw displayed formulae for X and Y. Formula X Y (b) Name compound Y.... (c) Compound Y mixes readily with water. Suggest a reason for this A. arman - moulsham high school 66

67 (d) (i) Draw the structural formula of an alcohol which could be used to prepare a sample of Y. What reagents would you use to prepare Y from the alcohol? (e) (i) The infra-red spectra of X and Y were compared with the infra-red spectrum of ethanol. The spectra of X and Y contain an absorption peak which is not present in the spectrum of ethanol. Identify the bond in X and Y which causes this peak. The spectrum of ethanol contains a broad peak which does not occur in the spectra of X or Y. Suggest which bond causes this peak and why the peak is broad. (Total 9 marks) 34. Study the reaction scheme below, then answer the questions that follow. (a) (i) Butanal contains a carbonyl group. State a chemical test for a carbonyl group and describe the result of the test. Test... Result... A. arman - moulsham high school 67

68 An isomer of butanal also possesses a carbonyl group, but cannot be oxidised by acidified sodium dichromate(vi). Give the structural formula of this isomer and its name. Structural formula... Name... (iii) Another isomer of butanal contains a carbonyl group and can be oxidised by acidified sodium dichromate(vi). Draw the displayed formula of this isomer. (b) Compound X is a colourless liquid that smells of pineapples. (i) To what class of compounds does X belong?... Ethanol, C 2 5 O, reacts with butanoic acid to form compound X. Complete the diagram below to show the structural formula of X and the other product. A. arman - moulsham high school 68

69 (iii) Give the name of compound X.... (iv) What type of attacking species is ethanol in this reaction?... (c) Describe what you would expect to see during Reaction A. arman - moulsham high school 69

70 (d) Explain why Reaction 4 is far more vigorous than Reaction (Total 12 marks) 35. The reaction sequence below shows a method that could be used to convert benzene into benzoic acid. (a) (i) Name the reagent and catalyst that could be used to convert benzene into A in Step 1. Reagent... Catalyst... Name the type of reaction in Step 1 and its mechanism. Type... Mechanism... (iii) Write an equation to show how the catalyst interacts with the reagent in Step 1 and explain how this helps the reaction to take place. Equation Explanation A. arman - moulsham high school 70