Advanced Subsidiary Unit 1: The Core Principles of Chemistry

Transcription

1 Write your name here Surname Other names Pearson Edexcel GCE Centre Chemistry Advanced Subsidiary Unit 1: The Core Principles of Chemistry Candidate Friday 22 May 2015 Morning Time: 1 hour 30 minutes Candidates may use a calculator. Paper Reference 6CH01/01 Total Marks P44879A 2015 Pearson Education Ltd. 6/6/6/6/ Instructions Use black ink or ball-point pen. Fill in the boxes at the top of this page with your name, centre number and candidate number. Answer all questions. Answer the questions in the spaces provided there may be more space than you need. Information The total mark for this paper is 80. The marks for each question are shown in brackets use this as a guide as to how much time to spend on each question. Questions labelled with an asterisk (*) are ones where the quality of your written communication will be assessed you should take particular care with your spelling, punctuation and grammar, as well as the clarity of expression, on these questions. A Periodic Table is printed on the back cover of this paper. Advice Read each question carefully before you start to answer it. Keep an eye on the time. Try to answer every question. Check your answers if you have time at the end. *P44879A0124* Turn over

2 SECTION A Answer ALL the questions in this section. You should aim to spend no more than 20 minutes on this section. For each question, select one answer from A to D and put a cross in the box. If you change your mind, put a line through the box and then mark your new answer with a cross. 1 Which molecule does not exhibit E / Z isomerism? A Br H 3 C C C CH 3 H B Br H C C CH 3 CH 3 C H 3 C H C C CH 2 Br H D Br H 3 C C C CH 3 Br (Total for Question 1 = 1 mark) 2 What is the systematic name for the compound with the following formula? CH 3 C 2 H 5 H 3 C CH CH 2 CH CH 3 A B C D 2-methyl-4-ethylpentane 2-ethyl-4-methylpentane 2,4-dimethylhexane 3,5-dimethylhexane (Total for Question 2 = 1 mark) 2 *P44879A0224*

3 3 Which of the following molecules is formed on adding bromine water to ethene? A B C D ethanol ethane-1,2-diol bromoethane 2-bromoethanol (Total for Question 3 = 1 mark) 4 A section of a polymer is shown below. CH 3 CH 3 CH 3 CH 3 C C C C C 2 H 5 H C 2 H 5 H What is the monomer for this polymer? CH 3 CH 3 A H C C H C 2 H 5 H CH 3 CH 3 CH 3 B C C C C C 2 H 5 CH 3 C 2 H 5 CH 3 CH 3 C C C C 2 H 5 H CH 3 H D CH 3 C C C 2 H 5 (Total for Question 4 = 1 mark) *P44879A0324* 3 Turn over

4 5 Which of the following equations has the correct state symbols for the reaction of dilute hydrochloric acid with magnesium oxide? A MgO(s) + 2HCl(aq) MgCl 2 (s) + H 2 O(l) B MgO(s) + 2HCl(aq) MgCl 2 (aq) + H 2 O(l) C MgO(s) + 2HCl(l) MgCl 2 (s) + H 2 O(l) D MgO(s) + 2HCl(l) MgCl 2 (aq) + H 2 O(l) (Total for Question 5 = 1 mark) 6 This question is about the reaction between sodium carbonate solution and dilute nitric acid. Na 2 CO 3 (aq) + 2HNO 3 (aq) 2NaNO 3 (aq) + CO 2 (g) + H 2 O(l) (a) What is the ionic equation for this reaction? A Na 2 CO 3 (aq) + 2H + (aq) 2Na + (aq) + CO 2 (g) + H 2 O(l) B Na + (aq) + NO 3 (aq) NaNO 3 (aq) C CO 3 2 _ (aq) + 2H + (aq) CO 2 (g) + H 2 O(l) D CO 3 2 _ (aq) + 2HNO 3 (aq) 2NO 3 (aq) + CO 2 (g) + H 2 O(l) (b) What is the volume of carbon dioxide produced from the complete reaction of 0.10 mol of nitric acid at room temperature and pressure? [1 mol of any gas occupies 24 dm 3 at room temperature and pressure.] A 1.2 dm 3 B 1.8 dm 3 C 2.4 dm 3 D 3.6 dm 3 (c) What volume of sodium carbonate solution of concentration mol dm 3, would be needed to completely react with 25.0 cm 3 of nitric acid of concentration mol dm 3? A 6.25 cm 3 B cm 3 C cm 3 D cm 3 (Total for Question 6 = 3 marks) 4 *P44879A0424*

5 7 Lithium reacts with water to produce hydrogen. Li(s) + H 2 O(l) LiOH(aq) + ½H 2 (g) (a) In an experiment, g (0.01 mol) of lithium produced 90 cm 3 of hydrogen at room temperature and pressure. What is the percentage yield of hydrogen? [1 mol of any gas occupies 24 dm 3 at room temperature and pressure.] A 45% B 60% C 75% D 90% (b) Which of the following is not a possible reason for the yield being less than 100%? A Some oil remained on the surface of the lithium. B C Hydrogen gas is very soluble in water. A layer of oxide was present on the surface of the lithium. D Some of the hydrogen gas escaped collection. (Total for Question 7 = 2 marks) 8 How many moles of atoms are present in 240 cm 3 of carbon dioxide at room temperature and pressure? [1 mol of any gas occupies 24 dm 3 at room temperature and pressure.] A B C D (Total for Question 8 = 1 mark) *P44879A0524* 5 Turn over

6 9 What is the percentage by mass of nitrogen in ammonium nitrate, NH 4 NO 3? [Molar masses/g mol 1 : N = 14.0; H = 1.0; O = 16.0] A 14.0% B 17.5% C 28.0% D 35.0% (Total for Question 9 = 1 mark) 10 The first five successive ionization energies for an element J, in kj mol _ 1, are 1st 2nd 3rd 4th 5th The formula of the compound of chlorine with element J is A JCl B JCl 2 C JCl 3 D J 2 Cl 3 (Total for Question 10 = 1 mark) 11 Which of the following is the correct order of increasing melting temperature of elements of Period 3? A Na, Mg, Al, Si B C Na, Mg, Si, Al Si, Na, Mg, Al D Si, Al, Mg, Na (Total for Question 11 = 1 mark) 6 *P44879A0624*

7 12 Which one of the following elements undergoes the change in electronic configuration shown when it forms the stated ion? Atom 1s 2 2s 2 2p 6 3s 2 3p 3 Ion 1s 2 2s 2 2p 6 3s 2 3p 6 A B to B 3+ B Al to Al 3+ C N to N 3 D P to P 3 (Total for Question 12 = 1 mark) 13 Which of the following compounds has the most polarized anion? A B C Na 2 O MgO K 2 O D CaO (Total for Question 13 = 1 mark) *P44879A0724* 7 Turn over

8 14 The diagram shows a Born-Haber cycle for calcium chloride. It is not drawn to scale. All units are in kj mol _ 1. Ca 2+ (g) + 2Cl _ (g) Q = R = ( 346 2) = 692 P = 2258 Ca(g) + 2Cl(g) +178 S = (+121 2) = +242 CaCl 2 (s) X =? Ca(s) + Cl 2 (g) (a) Which enthalpy change is correctly labelled on the diagram? A Enthalpy change for the formation of calcium chloride (P). B C First ionization energy of calcium (Q). Electron affinity of chlorine (R). D Twice the enthalpy change of atomization of chlorine (S). (b) What is the value of X, in kj mol _ 1? A +795 B 795 C D 3721 (Total for Question 14 = 2 marks) 8 *P44879A0824*

9 15 Calculate the enthalpy change, in kj mol _ 1, for the reaction DATA: H 2 (g) + ½O 2 (g) H 2 O(g) Bond Bond enthalpy / kj mol _ 1 H H +436 O=O +498 H O +464 A B C +6 D +221 (Total for Question 15 = 1 mark) 16 The chemical properties of an element are determined by its A B C electronic structure. number of neutrons. relative atomic mass. D number of protons plus neutrons. (Total for Question 16 = 1 mark) TOTAL FOR SECTION A = 20 MARKS *P44879A0924* 9 Turn over

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11 SECTION B Answer ALL the questions. Write your answers in the spaces provided. 17 This question is about the use of mass spectrometers. (a) Bromine has two isotopes, 79 Br and 81 Br. Explain the term isotopes, by reference to sub-atomic particles. (b) The presence and abundance of these isotopes can be determined by using a mass spectrometer such as that shown in the diagram below. sample vaporized + electric field + A B recorder ions are detected and recorded amplifier (i) Explain how ions are produced in the area labelled A. (2) (ii) State what is used to deflect the ions moving through the mass spectrometer in the area labelled B. (iii) Explain why there is a vacuum in a mass spectrometer. *P44879A01124* 11 Turn over

12 (c) Complete the mass spectrum below for a sample of bromine gas that contains approximately half 79 Br isotope and half 81 Br isotope. (4) Relative intensity m/e (d) Calculate the relative atomic mass of bromine for a sample which was found to contain 47.0% 79 Br and 53.0% 81 Br. Give your answer to three significant figures. (2) (e) What would be the effect, if any, on the m/e value of the peak if the ion detected had lost two electrons rather than one electron? 12 *P44879A01224*

13 *(f) One of the uses of mass spectrometers is for the detection of banned substances, such as anabolic steroids, in a blood or urine sample taken from competitors in sports events. (i) Suggest two precautions that are necessary to ensure that the result of any analysis would be valid. (2) (ii) These substances can give competitors an unfair advantage. Suggest why the use of these substances may be of concern to the user. (g) Suggest one other use for mass spectrometers. (Total for Question 17 = 16 marks) *P44879A01324* 13 Turn over

14 18 Alkenes and cycloalkanes have the same general formula, but react very differently with halogens. (a) Give the general formula that applies to both alkenes and cycloalkanes. (b) Using structural formulae, complete the overall equation for the reaction of an alkene of your own choice, containing fewer than four carbon atoms, with liquid bromine. Name the product. (3) + Br 2 Name: *P44879A01424*

15 *(c) An example of an alkene with six carbon atoms is 2-methylpent-1-ene. It reacts with chlorine by means of an electrophilic addition reaction. The diagram below shows a student s attempt at drawing the mechanism for this reaction. (i) Identify the three errors in this student s drawing of the mechanism. (3) Error 1... Error 2... Error 3... (ii) The structure of the carbocation intermediate is correctly drawn. Explain why the positive charge is on the carbon atom shown. *P44879A01524* 15 Turn over

16 (d) There are five possible cycloalkanes, each containing five carbon atoms. Three of the isomers are given below. Complete the other two boxes, by adding the skeletal formulae of the other two structural isomers. (2) (e) Define the term structural isomerism. (f) Another example of a cycloalkane is cyclobutane. This compound, like other cycloalkanes, can also react with chlorine. The overall reaction of cyclobutane with chlorine is as follows: C 4 H 8 + Cl 2 C 4 H 7 Cl + HCl (i) This reaction can occur at room temperature and pressure. What further condition is needed for this reaction to take place? (ii) Using the appropriate arrows, complete the equation for the initiation step of the reaction mechanism for the reaction of chlorine with cyclobutane. (2) Cl Cl 16 *P44879A01624*

17 (iii) Using molecular formulae, write equations for the two propagation steps of this mechanism. (2) First propagation step: Second propagation step: (iv) Name the type of bond fission which occurs in these propagation steps. (v) There are also termination steps in this mechanism. Explain how these differ from the other steps in the mechanism and why these result in the reaction ending. (2) (g) If the reaction with cyclobutane is carried out with an excess of chlorine, how are the products of the reaction affected? (Total for Question 18 = 20 marks) *P44879A01724* 17 Turn over

18 19 Sodium and chlorine react together to produce sodium chloride. The bonding in the product is different from that in both of the reactants. Evidence for the type of bonding present can be obtained in a number of different ways. (a) Draw the electron density map for a chlorine molecule to show covalent bonding. (b) Sodium chloride is ionically bonded. What is meant by the term ionic bond? (c) Electrolysis is an experiment which you could carry out in a school or college laboratory on an aqueous solution of sodium chloride, to provide evidence for the presence of ionic bonding. Draw a labelled diagram of the apparatus that you would use for this experiment, indicating how your results would show that the bonding was ionic. (3) 18 *P44879A01824*

19 (d) Chlorine gains an electron when it reacts with sodium to form sodium chloride. (i) Draw the dot and cross diagram of a chloride ion showing outer electrons only. (ii) Give the formula of an ion from Period 3 that is isoelectronic with the chloride ion. (e) Sodium and sodium chloride can both be good conductors of electricity. Under what conditions do these substances conduct electricity? Compare the method of conductivity in each case. (3) (Total for Question 19 = 10 marks) *P44879A01924* 19 Turn over

20 20 The reaction of calcium oxide with hydrochloric acid is an exothermic reaction. CaO(s) + 2HCl(aq) CaCl 2 (aq) + H 2 O(l) In an experiment to investigate this reaction, the following procedure was carried out cm 3 of hydrochloric acid, concentration 2.0 mol dm 3 (an excess), was pipetted into a polystyrene cup and the initial temperature measured using a thermometer with 0.5 C graduations g of calcium oxide powder was weighed out and added to the acid. The mixture was stirred and the maximum temperature measured. Maximum temperature / C 35.0 Initial temperature / C 19.5 (a) Calculate the enthalpy change, in joules, for the quantities in this experiment. Assume that the specific heat capacity of the solution is 4.18 J g 1 C 1. Use the expression: energy transferred in joules = 50.0 specific heat capacity temperature change (b) Using your answer from (a), calculate the molar enthalpy change for the reaction between calcium oxide and hydrochloric acid. Include a sign and units in your answer. (2) 20 *P44879A02024*

21 (c) The standard molar enthalpy change for the reaction between calcium oxide and hydrochloric acid is kj mol 1. (i) Suggest three reasons why the calculated value in part (b) is different from this value. (3) Reason 1... Reason 2... Reason 3... (ii) Using the standard enthalpy change of kj mol 1, calculate the minimum mass of calcium oxide that would be needed to raise the temperature of 250 cm 3 of hydrochloric acid (an excess) by 25.0 C. (3) *P44879A02124* 21 Turn over

22 (d) The reaction of calcium carbonate with hydrochloric acid has the following standard molar enthalpy change. H = 18.8 kj mol 1 This value can be used, with the enthalpy change for the reaction of calcium oxide with hydrochloric acid, to determine the enthalpy change for the thermal decomposition of calcium carbonate. This cannot be measured directly. (i) Complete the Hess energy cycle below by adding the missing arrow and entities. Use the cycle, and the standard enthalpy change for the reaction of calcium oxide and hydrochloric acid ( kj mol 1 ), to determine the standard enthalpy change for the decomposition of calcium carbonate. (4) CaCO 3 (s) CaO(s) + CO 2 (g) 2HCl(aq)... ( ) +... ( ) +... ( ) Enthalpy change =... kj mol 1 22 *P44879A02224*

23 (ii) Complete and label the enthalpy level diagram below, for the series of reactions in (d)(i). Your diagram does not have to be to scale. CaO(s) + CO 2 (g) Enthalpy / kj mol 1 CaCO 3 (s) Progress of reaction (Total for Question 20 = 14 marks) TOTAL FOR SECTION B = 60 MARKS TOTAL FOR PAPER = 80 MARKS *P44879A02324* 23

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25 Write your name here Surname Other names Pearson Edexcel GCE Centre Candidate Chemistry Advanced Subsidiary Unit 2: Application of Core Principles of Chemistry Tuesday 2 June 2015 Afternoon Time: 1 hour 30 minutes Candidates may use a calculator. Paper Reference 6CH02/01 Total Marks P44881A 2015 Pearson Education Ltd. 6/6/6/6/ Instructions Use black ink or ball-point pen. Fill in the boxes at the top of this page with your name, centre number and candidate number. Answer all questions. Answer the questions in the spaces provided there may be more space than you need. Information The total mark for this paper is 80. The marks for each question are shown in brackets use this as a guide as to how much time to spend on each question. Questions labelled with an asterisk (*) are ones where the quality of your written communication will be assessed you should take particular care with your spelling, punctuation and grammar, as well as the clarity of expression, on these questions. A Periodic Table is printed on the back cover of this paper. Advice Read each question carefully before you start to answer it. Keep an eye on the time. Try to answer every question. Check your answers if you have time at the end. *P44881A0124* Turn over

26 SECTION A Answer ALL the questions in this section. You should aim to spend no more than 20 minutes on this section. For each question, select one answer from A to D and put a cross in the box. If you change your mind, put a line through the box and then mark your new answer with a cross. 1 The bond angle in beryllium chloride, BeCl 2, is most likely to be A 90 B C 120 D 180 (Total for Question 1 = 1 mark) 2 Graphite and buckminsterfullerene are forms of carbon. Buckminsterfullerene dissolves in octane but graphite does not. This is because A B C the bonds between carbon atoms in buckminsterfullerene are weaker than those in graphite. buckminsterfullerene is molecular whereas graphite is a giant structure. graphite has delocalised electrons but buckminsterfullerene does not. D graphite has covalent bonds and London forces but buckminsterfullerene has just London forces. 3 Which of the following molecules is polar? A Carbon dioxide, CO 2 B Silicon tetrachloride, SiCl 4 C Ammonia, NH 3 D Boron trifluoride, BF 3 (Total for Question 2 = 1 mark) (Total for Question 3 = 1 mark) 2 *P44881A0224*

27 4 In which series of compounds does covalent character increase when going from left to right? A B KI, KBr, KCl NaI, KI, RbI C NaCl, MgCl 2, AlCl 3 D SO 2, P 4 O 10, SiO 2 (Total for Question 4 = 1 mark) 5 Hydrogen bromide has a lower boiling temperature than hydrogen iodide. This is because A B C hydrogen bromide has a smaller permanent dipole than hydrogen iodide. hydrogen bromide has weaker London forces than hydrogen iodide. hydrogen iodide forms hydrogen bonds but hydrogen bromide does not. D the H I bond is stronger than the H Br bond. (Total for Question 5 = 1 mark) *P44881A0324* 3 Turn over

28 6 Consider the following compounds, E, F, G and H. Cl CH 2 CH 2 CH 2 Cl CH 3 CH3 C E CH 3 CH 3 F l CH 2 CH 2 CH 2 CH 3 CH3 l C G CH 3 CH 3 H The boiling temperature of these compounds increases in the order A B C H G F E G H E F E F G H D F E H G (Total for Question 6 = 1 mark) 7 In which of the following reactions is sulfuric(iv) acid, H 2 SO 3, acting as an oxidizing agent? A H 2 SO 3 + H 2 O H 3 O + + HSO 3 B C H 2 SO 3 SO 2 + H 2 O H 2 SO 3 + 2FeCl 3 + H 2 O 2FeCl 2 + H 2 SO 4 + 2HCl D H 2 SO 3 + 2H 2 S 3H 2 O + 3S (Total for Question 7 = 1 mark) 4 *P44881A0424*

29 8 Which of the following properties decreases on descending Group 2 of the Periodic Table? A B C Solubility of the sulfates. Solubility of the hydroxides. Reactivity of the elements. D Ionic character of the oxides. (Total for Question 8 = 1 mark) 9 Compound X is an anhydrous, white solid which decomposes on heating to form a white solid residue, a colourless gas, and a colourless vapour which condenses to a colourless liquid. Compound X is A B C sodium carbonate. sodium hydrogencarbonate. sodium nitrate. D sodium sulfate. (Total for Question 9 = 1 mark) *P44881A0524* 5 Turn over

30 10 These questions concern the Maxwell-Boltzmann energy distribution shown below. Fraction of particles with a specific energy Energy E a (a) What is the best way to describe the activation energy, E a, of a reaction? A The average energy of the particles that react. B C The minimum energy required for a reaction to occur. The energy difference between the reactants and products. D The energy produced by the particles that react. (b) How does the curve above change when the temperature is increased? A The peak increases in height and moves to the left. B C The peak increases in height and moves to the right. The peak decreases in height and moves to the left. D The peak decreases in height and moves to the right. 6 *P44881A0624*

31 (c) What would be the effect on the diagram if the reactant concentrations were increased? A There would be no change. B C The E a line would move to the right. The E a line would move to the left. D The peak decreases in height and moves to the right. (d) What would be the effect on the diagram if a catalyst was added? The activation energy would A be unchanged and the peak would move to the right. B C move to the left and the peak would move to the right. move to the left and the peak would move to the left. D move to the left and the peak would be unchanged. (Total for Question 10 = 4 marks) 11 Propanal, CH 3 CH 2 CHO, and propanone, CH 3 COCH 3, are carbonyl compounds. When these compounds are compared using physical methods of analysis, which of the following statements is not correct? A B C The compounds produce different patterns in the fingerprint region of the IR spectrum. The carbonyl groups absorb at frequencies in the same region of the IR spectrum. The compounds produce different fragmentation patterns in a mass spectrum. D The compounds have molecular ion peaks at different mass to charge ratios in a mass spectrum. (Total for Question 11 = 1 mark) *P44881A0724* 7 Turn over

32 12 A sample of propanone, CH 3 COCH 3, was heated under reflux with potassium dichromate(vi) acidified with sulfuric acid, and then the mixture was distilled. Apart from the peaks due to the C C and C H bonds, what peak(s) would be present in the IR spectrum of the distillate? A A peak due to the C O only. B A peak due to the O H only. C Peaks due to C O and O H. D Peaks due to C O, C O and O H. (Total for Question 12 = 1 mark) 13 Which of the following describes the appearance of iodine under the stated conditions? Solid Dissolved in aqueous potassium iodide Dissolved in a liquid hydrocarbon A purple brown purple B brown blue-black yellow C shiny grey brown purple D shiny grey brown brown (Total for Question 13 = 1 mark) 14 Why do calculations of global warming exclude the effect of water vapour in the atmosphere? A B C Water vapour is not a greenhouse gas. Water vapour is a much less potent greenhouse gas than carbon dioxide. The average concentration of water vapour in the atmosphere is fairly constant. D The concentration of water vapour in the atmosphere is much lower than that of carbon dioxide. (Total for Question 14 = 1 mark) 8 *P44881A0824*

33 15 A compound of nitrogen and hydrogen only is analyzed and found to contain 97.7% by mass of nitrogen. What is the empirical formula of the compound? Molar masses /g mol 1 : H = 1; N = 14 A NH 3 B NH 2 C N 3 H 5 D N 3 H (Total for Question 15 = 1 mark) 16 Chlorofluorocarbons, CFCs, damage the ozone layer. The mechanism of the process involves A B C homolytic fission. heterolytic fission. electrophilic addition. D nucleophilic substitution. (Total for Question 16 = 1 mark) 17 Electrophiles are A B C electron pair donors that are attracted to regions of high electron density. electron pair donors that are attracted to regions of low electron density. electron pair acceptors that are attracted to regions of high electron density. D electron pair acceptors that are attracted to regions of low electron density. (Total for Question 17 = 1 mark) TOTAL FOR SECTION A = 20 MARKS *P44881A0924* 9 Turn over

34 SECTION B Answer ALL the questions. Write your answers in the spaces provided. 18 Halogenoalkanes react slowly with water to form alcohols. The equation for the reaction is RX + H 2 O ROH + H + + X (a) The rate of this reaction for different halogenoalkanes was investigated using the apparatus below. In one experiment, equal amounts of 1-chlorobutane, 1-bromobutane and 1-iodobutane were placed in separate test tubes with 5 cm 3 of ethanol. These test tubes were placed in the water bath together with a test tube containing aqueous silver nitrate. After about 5 minutes, 1 cm 3 of the silver nitrate solution was added to each test tube containing a halogenoalkane and the time taken for a precipitate to form in each test tube was noted. The temperature of the water bath was maintained at 50 C. (i) Why is ethanol used as a solvent in this experiment? (ii) Explain why the apparatus was left for 5 minutes before the silver nitrate was added. 10 *P44881A01024*

35 (iii) Name the precipitate formed in the test tube containing 1-bromobutane and write an ionic equation for the formation of this precipitate. State symbols are not required. (2) Precipitate... Ionic equation (iv) Predict the order (fastest first) in which the halogenoalkanes form precipitates. Explain your answer. (2) Order... Explanation... (b) Alcohols are usually prepared from halogenoalkanes using aqueous alkali, rather than water, as the reaction is faster. (i) Name the mechanism and type of reaction occurring when 1-bromobutane reacts with aqueous alkali. (2) *P44881A01124* 11 Turn over

36 (ii) Explain why the formation of alcohols is faster with aqueous alkali than with water. (iii) Give the mechanism for the reaction of 1-bromobutane with aqueous alkali. Show the lone pair involved in the mechanism and any relevant dipoles and curly arrows. (3) 12 *P44881A01224*

37 (iv) One student suggested that the final reaction mixture could be tested for the presence of an alcohol using phosphorus(v) chloride while another suggested using potassium dichromate(vi) with sulfuric acid. Describe the result of a positive test for alcohols using each of these reagents. Explain which test is better for the final reaction mixture. (3) Observation with PCl 5... Observation with acidified K 2 Cr 2 O 7... Explanation... (c) 1-bromobutane is classified as a primary halogenoalkane and is one of the four structural isomers with a molecular formula C 4 H 9 Br. Give the skeletal formula of the three isomers, other than 1-bromobutane, classifying the halogenoalkane in each case. (3) Skeletal formula Classification (Total for Question 18 = 18 marks) *P44881A01324* 13 Turn over

38 19 Two white powders, A and B, known to be Group 2 carbonates, are investigated. (a) (i) The presence of the carbonate ion is usually confirmed using a simple test carried out in two stages at room temperature. Describe this test and its results. (2) Test... Results... (ii) Using barium carbonate as your example, write the equation for each of the stages of the carbonate test. Include state symbols in both equations. (3) First equation (test) Second equation (result) 14 *P44881A01424*

39 (b) When a flame test is carried out on the two powders, A gives no colour and B gives a yellow-red flame. (i) Describe how a flame test is carried out. (3) (ii) Give the formulae of the metal ions in A and B. (2) A... B... *(iii) Explain the origin of the flame colour. (3) (iv) Suggest why compound A produces no flame colour. *P44881A01524* 15 Turn over

40 *(c) When Group 2 metal carbonates are heated strongly, they decompose forming the metal oxide and carbon dioxide. Explain why the thermal stability of the metal carbonates increases as the group is descended. (3) (Total for Question 19 = 17 marks) 16 *P44881A01624*

41 20 Induced hydraulic fracturing, commonly known as fracking, which was developed in 1947, is a technique for extracting natural gas (mainly methane) from shale deposits. While natural gas is a much cleaner fuel than coal, it is difficult to carry out fracking without leakage. Because methane is a far more potent greenhouse gas than carbon dioxide, it has been calculated that leakage rates of around 2% are sufficient to increase global warming. (a) Suggest what is meant by natural gas is a much cleaner fuel than coal. (b) Explain how greenhouse gases cause global warming. (2) (c) Suggest why methane is a far more potent greenhouse gas than carbon dioxide. (Total for Question 20 = 4 marks) TOTAL FOR SECTION B = 39 MARKS *P44881A01724* 17 Turn over

42 SECTION C Answer ALL the questions. Write your answers in the spaces provided. 21 Swimming Pool Chemistry The circulation of water in swimming pools is much slower than that in most natural water courses, but the number of people using a given volume of water is often far greater. If steps are not taken to keep microorganisms and other contaminants under control, the water will become hazardous. Filters are used to remove solid material and chemicals are added to disinfect the water. The most common method of disinfection involves the use of chlorine compounds, but systems using bromine have advantages. These systems depend on their oxidizing properties. With chlorine systems, the key species is the chlorate(i) ion (OCl ) which kills bacteria by damaging the structure of their cell walls and disrupting enzyme activity. A simple way of adding chlorate(i) ions to water is by using chlorine. The weak acid, chloric(i) acid (HOCl), is formed and this dissociates producing the chlorate(i) ion. (a) The equation for the reaction of chlorine with water is: Cl 2 (aq) + H 2 O(l) HOCl(aq) + HCl(aq) By referring to the relevant oxidation numbers, explain why this is a disproportionation reaction. (3) 18 *P44881A01824*

43 (b) (i) Complete the dot and cross diagram for chloric(i) acid (HOCl). Use a dot ( ) to represent the hydrogen electron, circles (o) to represent the oxygen electrons and crosses ( ) to represent the chlorine electrons. Show the outer electrons only, but include non-bonding electrons. (2) H O Cl *(ii) Predict the bond angle in chloric(i) acid. Explain your answer fully. (5) Bond angle =... *P44881A01924* 19 Turn over

44 (c) If the concentration of chlorate(i) ions in a swimming pool is too low, bacteria will flourish. If it is too high, swimmers will be harmed. In the United Kingdom, it is recommended that the concentration of chlorine be in the range 1 2 mg dm 3. The total amount of chlorine, Cl 2, present can be measured by titration. In such a determination, excess sulfuric acid and potassium iodide were added to a 1.00 dm 3 sample of swimming pool water and the resulting solution required 9.65 cm 3 of mol dm 3 sodium thiosulfate for complete reaction. The equations for the reactions are: Cl 2 + 2I I 2 + 2Cl I 2 + 2S 2 O 3 2 2I + S 4 O 6 2 (i) Show that the concentration of chlorine, Cl 2, in this sample meets the UK recommended requirements. All steps in your calculation must be shown. (3) 20 *P44881A02024*

45 (ii) Analysing a single sample of swimming pool water in this way is likely to give unreliable results because it is not possible to repeat the titration. Suggest another way in which this method is unreliable. (d) One advantage of the bromine disinfection system is that, while chloric(i) acid decomposes in sunlight forming hydrogen chloride and oxygen, bromic(i) acid (HOBr) is stable. Another advantage is that bromine is less volatile than chlorine. (i) Write an equation for the decomposition of chloric(i) acid in sunlight. State symbols are not required. (ii) Explain why bromine is less volatile than chlorine. (2) *P44881A02124* 21 Turn over

46 (e) The ph of the swimming pool affects the performance of the disinfectant. The data below show how the concentrations of bromine species vary with ph. ph % bromine as HOBr % bromine as OBr The equation for the reaction of bromic(i) acid in water is HOBr(aq) H + (aq) + OBr (aq) (i) Assume the ph of the swimming pool is neutral. Explain how any changes in the ph of the swimming pool affect the concentration of the bromine species. (3) (ii) The higher the concentration of bromate(i) ions, the more effective the disinfectant. Suggest a disadvantage of too high a ph. (Total for Question 21 = 21 marks) TOTAL FOR SECTION C = 21 MARKS TOTAL FOR PAPER = 80 MARKS 22 *P44881A02224*

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49 Write your name here Surname Other names Pearson Edexcel GCE Centre Candidate Chemistry Advanced Unit 4: General Principles of Chemistry I Rates, Equilibria and Further Organic Chemistry (including synoptic assessment) Wednesday 10 June 2015 Afternoon Time: 1 hour 40 minutes Paper Reference 6CH04/01 You must have: Data Booklet Total Marks Candidates may use a calculator. P42978A 2015 Pearson Education Ltd. 5/5/6/5/1/1/1/ Instructions Use black ink or ball-point pen. Fill in the boxes at the top of this page with your name, centre number and candidate number. Answer all questions. Answer the questions in the spaces provided there may be more space than you need. Information The total mark for this paper is 90. The marks for each question are shown in brackets use this as a guide as to how much time to spend on each question. Questions labelled with an asterisk (*) are ones where the quality of your written communication will be assessed you should take particular care with your spelling, punctuation and grammar, as well as the clarity of expression, on these questions. A Periodic Table is printed on the back cover of this paper. Advice Read each question carefully before you start to answer it. Keep an eye on the time. Try to answer every question. Check your answers if you have time at the end. *P42978A0128* Turn over

50 SECTION A Answer ALL the questions in this section. You should aim to spend no more than 20 minutes on this section. For each question, select one answer from A to D and put a cross in the box. If you change your mind, put a line through the box and then mark your new answer with a cross. 1 Name the compound below. CH 3 Cl C C H CH 2 CH 3 A B C D E-2-chloropent-2-ene Z-2-chloropent-3-ene E-2-chloropent-3-ene Z-2-chloropent-2-ene (Total for Question 1 = 1 mark) Use this space for any rough working. Anything you write in this space will gain no credit. 2 *P42978A0228*

51 2 Which of the following compounds is not chiral? A O B C HO NH 2 O OH HO D O OH (Total for Question 2 = 1 mark) Use this space for any rough working. Anything you write in this space will gain no credit. *P42978A0328* 3 Turn over

52 3 Calculate the ph of a solution of HCl, of concentration 0.25 mol dm 3. A 0.60 B 0.25 C 0.60 D 1.39 (Total for Question 3 = 1 mark) 4 Which gas is the least suitable as a carrier gas in Gas-Liquid Chromatography? A B C D Argon Carbon dioxide Oxygen Nitrogen (Total for Question 4 = 1 mark) 5 What are the units of the equilibrium constant (K c ) for the hypothetical reaction below? A mol 2 dm 9 B mol 2 dm 9 C mol 2 dm 6 D mol 2 dm 6 2A(aq) + B(aq) 4C(aq) + D(aq) (Total for Question 5 = 1 mark) Use this space for any rough working. Anything you write in this space will gain no credit. 4 *P42978A0428*

53 6 This question is about the reversible reaction below. 2NO 2 (g) N 2 O 4 (g) (a) A chemist investigating this reaction started with 10 moles of NO 2 and allowed the system to reach equilibrium. If 3 moles of N 2 O 4 are formed, the number of moles of NO 2 at equilibrium is A 8.5 B 7 C 6 D 4 (b) Under different conditions, 40% of the moles present at equilibrium is N 2 O 4. If the total pressure of the system is 2.0 atm, the numerical value of the equilibrium constant, K p is A 0.56 B 0.67 C 1.5 D 1.8 (Total for Question 6 = 2 marks) Use this space for any rough working. Anything you write in this space will gain no credit. *P42978A0528* 5 Turn over

54 7 Carbon monoxide and chlorine react together and reach equilibrium: CO(g) + Cl 2 (g) COCl 2 (g) If the pressure of the system is then increased at constant temperature, which of the following statements is correct? A B C D The equilibrium moves to the left and K p decreases. The equilibrium moves to the right and K p increases. The equilibrium moves to the right, then back to the left and K p remains the same. The equilibrium moves to the right and K p remains the same. (Total for Question 7 = 1 mark) 8 The table shows some data about metal ions, non-metal ions and their compounds. Ion Use the data to calculate Mg 2+ (g) 1921 Cl (g) 340 Cs + (g) 276 F (g) 483 Enthalpy change of hydration / kj mol 1 Compound Lattice energy / kj mol 1 MgCl 2 (s) 2526 CsF(s) 747 (a) the standard enthalpy change, in kj mol 1, for the following process. A 1241 B 1581 C 2261 D 2601 Mg 2+ (g) + 2Cl (g) Mg 2+ (aq) + 2Cl (aq) 6 *P42978A0628*

55 (b) the standard enthalpy change of solution, in kj mol 1, of caesium fluoride, CsF. A 12 B +12 C 1506 D (Total for Question 8 = 2 marks) 9 Which of these solvents is most likely to be warmed by microwave radiation? A B C Hexane Cyclohexane Cyclohexanol D Cyclohexene (Total for Question 9 = 1 mark) Use this space for any rough working. Anything you write in this space will gain no credit. *P42978A0728* 7 Turn over

56 10 Some chemical tests are described below. A B C Warm with Fehling s (or Benedict s) solution Warm with acidified potassium dichromate(vi) solution Add sodium carbonate solution D Add 2,4-dinitrophenylhydrazine solution (a) Which test always gives a positive result with carbonyl compounds? A B C D (b) Which test would give a positive result with ethane-1,2-diol? A B C D (c) Which test would result in effervescence with ethanoic acid? A B C D (Total for Question 10 = 3 marks) Use this space for any rough working. Anything you write in this space will gain no credit. 8 *P42978A0828*

57 11 Consider the four compounds shown below. A CH 3 COOCH 3 B CH 3 COOH C CH 3 CONHCH 2 CH 3 D CH 3 COCl Which of these compounds (a) will react most vigorously with water? A B C D (b) forms methanol when refluxed with aqueous sodium hydroxide? A B C D (c) has at least one triplet in its high resolution proton nmr spectrum? A B C D (Total for Question 11 = 3 marks) Use this space for any rough working. Anything you write in this space will gain no credit. *P42978A0928* 9 Turn over

58 12 The diagram below shows part of the mechanism for the nucleophilic addition of hydrogen cyanide to butanone. O H 3 C C C H 2 CH 3 Step 1 Intermediate X Step 2 CN Organic Products (a) The formula of the intermediate X is OCN A C + H 3 C C H 2 CH 3 O B H 3 C C CN C H 2 CH 3 O C H 3 C C CN C H 2 CH 3 OH + D H 3 C C CN C H 2 CH 3 10 *P42978A01028*

59 (b) Consider the dissociation of the weak acid, HCN. HCN(aq) H + (aq) + CN (aq) Which of the following reagents would shift the position of the equilibrium towards formation of the nucleophile, CN? A KOH B KCN C H 2 SO 4 D CH 3 COOH (c) Which statement about the mixture of organic products formed is not correct? A The mixture contains products with chiral molecules. B C The mixture rotates the plane of plane-polarized light. The mixture contains products with the nitrile functional group. D The mixture contains products each of which has four carbon atoms in a straight chain. (Total for Question 12 = 3 marks) TOTAL FOR SECTION A = 20 MARKS *P42978A01128* 11 Turn over

60 SECTION B Answer ALL the questions. Write your answers in the spaces provided. 13 A student carried out a titration by adding mol dm 3 potassium hydroxide solution to 25.0 cm 3 of mol dm 3 propanoic acid. A sketch graph of ph against volume of potassium hydroxide solution added is shown below. 14 ph 7 0 Vol of KOH / cm 3 (a) *(i) Describe and explain the behaviour of the solution formed in the region circled on the sketch graph. (3) 12 *P42978A01228*

61 *(ii) Explain why the ph at the equivalence point of this titration is greater than 7. (3) (iii) By considering the amount of excess alkali remaining, calculate the ph of the solution formed when 40 cm 3 of mol dm 3 potassium hydroxide solution has been added to 25.0 cm 3 of mol dm 3 propanoic acid. K w = mol 2 dm 6 at 298 K (5) *P42978A01328* 13 Turn over

62 (b) The student made the following statement: The ph of pure water is always 7.0 Is the student correct? Use the following information to justify your answer. H 2 O(l) H + (aq) + OH (aq) K w = 1.0 x mol 2 dm 6 at 298 K H is positive for the forward reaction in the equilibrium. (3) (Total for Question 13 = 14 marks) 14 *P42978A01428*

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64 14 The kinetics of the fast reaction below were investigated in a series of experiments. catalyst X A + B C + D H is negative (a) Outline a titrimetric method that could be used to measure the change in concentration of compound A with time. Compound A is an alkali, whereas compounds B, C and D are neutral. (3) 16 *P42978A01628*

65 (b) The rate of the reaction was measured at several different concentrations of A, in the presence of a large excess of compound B and a constant amount of catalyst X, to find the order of reaction with respect to A. The results are shown on the graph below. anomalous results Rate / mol dm 3 s 1 [A] / mol dm 3 (i) Explain how the graph confirms that the reaction is first order with respect to A. (ii) Suggest an explanation, other than human error, for the two anomalous results circled on the graph. (3) *P42978A01728* 17 Turn over

66 (c) In a second series of experiments, further data were collected using an initial rates method. These results are summarised in the table below. Experiment Initial concentration / mol dm 3 A B X Initial rate / mol dm 3 s (i) Give one reason why obtaining these further data may be considered useful. 18 *P42978A01828*

67 (ii) Deduce the rate equation for this reaction, explaining how you arrived at your answer. (5) (iii) Use your answer from (c)(ii), and appropriate data from Experiment 4, to calculate the value of the rate constant, k. Include units in your answer. (2) *P42978A01928* 19 Turn over

68 (d) A student carried out a similar investigation into the kinetics of the reaction between 2-bromomethylpropane and hydroxide ions. A summary of the student s findings is shown below. Kinetics Investigation - Summary of Key Findings Reaction is first order with respect to 2-bromomethylpropane Suggested Mechanism S N 2 - as two steps in process H 3 C CH 3 C Br Step 1 Fast H 3 C CH 3 C + + Br CH 3 CH 3 H 3 C CH 3 C + + OH Step 2 Slow H 3 C CH 3 C OH CH 3 CH 3 Use your knowledge of the mechanism of nucleophilic substitution reactions to suggest one feature of the summary, including the student s mechanism, that you agree with and two features you think are incorrect. (3) One feature you agree with. Two features you think are incorrect. (Total for Question 14 = 18 marks) 20 *P42978A02028*

69 15 Aspirin can be manufactured from sodium phenoxide using the process shown below. (s) ONa Sodium phenoxide + CO 2 (g) OH Step 1 Step 2 COONa (s) Step 3 OH COOH (s) Overall yield for process = 79% OCOCH 3 (a) Explain one effect of an increase in pressure on the reaction in Step 1. Aspirin COOH (2) (s) (b) The overall yield for this process is 79%. Calculate the mass, in tonnes, of aspirin that would be formed from 2.5 tonnes of sodium phenoxide. Give your answer to two significant figures. [Molar masses / g mol 1 : sodium phenoxide = 116; aspirin = 180] (3) (c) Classify the reaction type in Step 3 and suggest a suitable reagent. (2) Reaction type... Reagent... (Total for Question 15 = 7 marks) *P42978A02128* 21 Turn over

70 16 Fresh coffee is made by adding hot water to ground coffee beans. Chemists at the University of Nevada have produced bio-diesel fuel from used coffee grounds. The grounds contain approximately 10 15% oil by mass. This oil can be extracted, using standard chemical techniques, and then converted to bio-diesel by the reaction with methanol in the presence of a suitable catalyst. (a) (i) A solvent is added to the solid coffee grounds to dissolve the oil. Suggest how the oil is then obtained from this mixture. (2) (ii) Complete the equation below for the formation of a bio-diesel from the reaction of an oil with methanol. (2) CH 2 OOCR 3CH 3 OH + CHOOCR CH 2 OOCR (iii) Suggest a suitable catalyst for the reaction in (a)(ii). 22 *P42978A02228*

71 *(b) Another source of oil for bio-diesel production is palm oil, obtained from the fruit of palm trees grown on large plantations across many tropical regions. Consider one advantage and one disadvantage of each source to decide which oil may provide a potentially greener and more sustainable supply of bio-diesel. (4) (Total for Question 16 = 9 marks) TOTAL FOR SECTION B = 48 MARKS *P42978A02328* 23 Turn over

72 SECTION C Answer ALL the questions. Write your answers in the spaces provided. 17 Adipic acid, HOOC(CH 2 ) 4 COOH, is a dicarboxylic acid used in the production of polymers. It can be made by the reaction of buta-1,3-diene with carbon monoxide and water. CH 2 CHCHCH 2 (g) + 2CO(g) + 2H 2 O(l) HOOC(CH 2 ) 4 COOH(s) (a) (i) Use the Data Booklet to complete the table below. (2) CH 2 CHCHCH 2 (g) CO(g) H 2 O(l) HOOC(CH 2 ) 4 COOH(s) H f / kj mol S / J mol 1 K (ii) Use data from the table to calculate the standard enthalpy change, in kj mol 1, when adipic acid is formed from buta-1,3-diene, carbon monoxide and water. (2) (iii) Use data from the table to calculate the standard entropy change of the system, in J mol 1 K 1, when adipic acid is formed from buta-1,3-diene, carbon monoxide and water. (2) 24 *P42978A02428*

73 (iv) Use your answers to (a)(ii) and (a)(iii) to calculate S surroundings and S total for the reaction at 298 K. (3) (v) It was suggested that decreasing the temperature of the reaction to less than 298 K would produce a greater yield of adipic acid. Explain, in terms of the effect on S system, S surroundings and hence S total, whether this would be the case. (3) (b) Infrared spectroscopy can be used to follow the progress of reactions. During the reaction to produce adipic acid, suggest one peak which diminishes and one peak which appears. Use information from the Data Booklet to identify two such possible peaks, giving their wave numbers and the bonds involved. (2) *P42978A02528* 25 Turn over

74 (c) Adipic acid is used as an additive in some fruit jellies. Suggest what effect the adipic acid will have on the flavour of the jelly. (d) An organic compound, Q, is found to contain 49.3% carbon and 6.8% hydrogen by mass. (i) Use these data to confirm its empirical formula is C 3 H 5 O 2. (3) 26 *P42978A02628*

75 (ii) The structure of Q is shown below. H 3 C O H 2 C C O The table below summarises some information about parts of the nmr spectrum of compound Q. Use the Data Booklet, and your knowledge of splitting patterns, to complete the table with respect to the features of compound Q shown in bold. H C CH 3 C OH O (4) Feature of compound Q Chemical shift / ppm Splitting pattern CH CH 2 COOH singlet (Total for Question 17 = 22 marks) TOTAL FOR SECTION C = 22 MARKS TOTAL FOR PAPER = 90 MARKS *P42978A02728* 27

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77 Write your name here Surname Other names Pearson Edexcel GCE Centre Candidate Chemistry Advanced Unit 5: General Principles of Chemistry II Transition Metals and Organic Nitrogen Chemistry (including synoptic assessment) Monday 15 June 2015 Afternoon Time: 1 hour 40 minutes Paper Reference 6CH05/01 You must have: Data Booklet Total Marks Candidates may use a calculator. P45073RA 2015 Pearson Education Ltd. 6/6/6/6/1/2/ Instructions Use black ink or ball-point pen. Fill in the boxes at the top of this page with your name, centre number and candidate number. Answer all questions. Answer the questions in the spaces provided there may be more space than you need. Information The total mark for this paper is 90. The marks for each question are shown in brackets use this as a guide as to how much time to spend on each question. Questions labelled with an asterisk (*) are ones where the quality of your written communication will be assessed you should take particular care with your spelling, punctuation and grammar, as well as the clarity of expression, on these questions. A Periodic Table is printed on the back cover of this paper. Advice Read each question carefully before you start to answer it. Keep an eye on the time. Try to answer every question. Check your answers if you have time at the end. *P45073RA0128* Turn over

78 SECTION A Answer ALL the questions in this section. You should aim to spend no more than 20 minutes on this section. For each question, select one answer from A to D and put a cross in the box. If you change your mind, put a line through the box and then mark your new answer with a cross. 1 Which of the following is a redox reaction? A Cr 2 O OH 2CrO H 2 O B [Cu(H 2 O) 6 ] Cl [CuCl 4 ] 2 + 6H 2 O C 4OH + 4MnO 4 D [Fe(H 2 O) 6 ] OH 4MnO H 2 O + O 2 [Fe(H 2 O) 3 (OH) 3 ] + 3H 2 O (Total for Question 1 = 1 mark) 2 The oxidation state of nickel is not +2 in A [Ni(CO) 4 ] B [Ni(H 2 O) 4 (OH) 2 ] C [Ni(NH 3 ) 6 ] 2+ D [Ni(CN) 4 ] 2 (Total for Question 2 = 1 mark) 3 Which of the statements about a standard hydrogen electrode, for which E = 0 V, is correct? A A suitable solution for use in the electrode is hydrochloric acid with a concentration of 0.1 mol dm 3. B The pressure of the hydrogen has no effect on the value of E. C The metal used in the electrode is platinum. D The temperature is 273 K. (Total for Question 3 = 1 mark) Use this space for any rough working. Anything you write in this space will gain no credit. 2 *P45073RA0228*

79 4 The table below gives the standard electrode potentials of three half cells. System E /V H + (aq) + e ½H 2 (g) 0.00 Ag + (aq) + e Ag(s) Ag 2+ (aq) + e Ag + (aq) From these data it may be deduced that, under standard conditions, A Ag is a stronger reducing agent than H 2. B C D Ag 2+ ions are stronger oxidizing agents than H + ions. Ag + ions will disproportionate. Ag + ions will react with H + ions. (Total for Question 4 = 1 mark) 5 The value of E cell indicates whether the cell reaction is thermodynamically feasible. Which of the following is a correct statement about E cell? A E cell is directly proportional to the equilibrium constant. B E cell is directly proportional to the entropy change of the system, S system. C E cell is directly proportional to the total entropy change, S total. D The value of In E cell is directly proportional to the total entropy change, S total. (Total for Question 5 = 1 mark) 6 In a methanol fuel cell, the following half-reaction occurs CH 3 OH(l) + H 2 O(l) 6H + (aq) + CO 2 (g) + 6e The half-reaction occurring in the other half of the fuel cell is A H 2 (g) + O 2 (g) + 2e 2OH (aq) B 2H + (aq) + ½O 2 (g) + 2e H 2 O(l) C 2OH (aq) H 2 (g) + O 2 (g) + 2e D H 2 O(l) 2H + (aq) + ½O 2 (g) + 2e (Total for Question 6 = 1 mark) *P45073RA0328* 3 Turn over

80 7 Which of the following statements about fuel cells is not true? A B C D Reactants must constantly be fed into the cell when it is in use. Fuel cells are 100% efficient. Fuel cells convert chemical energy directly into electrical energy. Fuel cells produce electricity more efficiently than a diesel generator. (Total for Question 7 = 1 mark) 8 Copper(II) ions combine with three molecules of 1,2-diaminoethane, NH 2 CH 2 CH 2 NH 2, to form a complex ion. A bond angle, N Cu N, in this complex is A 120 B C 107 D 90 (Total for Question 8 = 1 mark) 9 Which of the following does not have a central metal ion having six bonds and an oxidation state of +2? A [Cu(C 2 O 4 ) 3 ] 4 B [Co(CN) 5 (H 2 O)] 3 C [Fe(CN) 6 ] 3 D [Zn(OH) 4 (H 2 O) 2 ] 2 (Total for Question 9 = 1 mark) 10 The reaction is an example of [Fe(H 2 O) 6 ] 2+ + H 2 O [Fe(H 2 O) 5 (OH)] + + H 3 O + A B C oxidation. reduction. ligand exchange. D acid-base behaviour. (Total for Question 10 = 1 mark) 4 *P45073RA0428*

81 11 Hydrated crystals of a compound have the formula CrCl 3 (H 2 O) 6. A solution containing one mole of the compound reacts with two moles of silver nitrate to form two moles of silver chloride. The complex chromium ion in the compound is most likely to be A [Cr(H 2 O) 3 Cl 3 ] 3+ B [Cr(H 2 O) 4 Cl 2 ] + C [Cr(H 2 O) 5 Cl] 2+ D [Cr(H 2 O) 6 ] 3+ (Total for Question 11 = 1 mark) 12 A heterogeneous catalyst is often preferred to a homogenous catalyst for an industrial process because A B C it is easily separated from the products. it has empty d-orbitals. it has more than one oxidation state. D it cannot be poisoned. (Total for Question 12 = 1 mark) 13 In the reaction of benzene with chloromethane, aluminium chloride is added because it reacts with A B C D benzene to produce an electrophile. benzene to produce a nucleophile. chloromethane to produce a nucleophile. chloromethane to produce an electrophile. (Total for Question 13 = 1 mark) 14 The reaction below can be catalysed by either Fe 2+ ions or Fe 3+ ions. This is because S 2 O 8 2 (aq) + 2I (aq) 2SO 4 2 (aq) + I 2 (aq) A B C both reactants can react with Fe 2+ ions. both reactants can react with Fe 3+ ions. S 2 O 8 2 ions can be oxidized by Fe 3+ ions and I ions can be reduced by Fe 2+ ions. D S 2 O 8 2 ions can be reduced by Fe 2+ ions and I ions can be oxidized by Fe 3+ ions. (Total for Question 14 = 1 mark) *P45073RA0528* 5 Turn over

82 15 The enthalpy changes of the reactions below are similar. The equilibrium constants for the two reactions are K 1 and K 2 respectively. Reaction 1 [Cu(H 2 O) 6 ] 2+ (aq) + EDTA 4 (aq) [Cu(EDTA)] 2 (aq) + 6H 2 O(l) Reaction 2 [Cu(H 2 O) 6 ] 2+ (aq) + 4Cl (aq) [CuCl 4 ] 2 (aq) + 6H 2 O(l) The value of K 1 is greater than K 2 because A S system is much more positive in Reaction 1. B S surroundings is much more positive in Reaction 1. C the EDTA 4 is more highly charged than Cl. D a lower concentration of EDTA 4 is needed than Cl. (Total for Question 15 = 1 mark) 16 Which of the following reacts with benzene under suitable conditions to form C 6 H 5 COC 6 H 5? A B C C 6 H 5 CHO C 6 H 5 COOH C 6 H 5 CH 2 OH D C 6 H 5 COCl (Total for Question 16 = 1 mark) 17 Benzene is converted to benzenesulfonic acid, C 6 H 5 SO 3 H, by reaction with A sulfuric(iv) acid, H 2 SO 3. B sulfuric(vi) acid, H 2 SO 4. C sulfur dioxide dissolved in sulfuric(iv) acid. D sulfur trioxide dissolved in sulfuric(vi) acid. (Total for Question 17 = 1 mark) Use this space for any rough working. Anything you write in this space will gain no credit. 6 *P45073RA0628*

83 18 Benzene reacts with chlorine to produce 1,2,3,4,5,6-hexachlorocyclohexane, C 6 H 6 Cl 6, by A B C free radical addition. free radical substitution. electrophilic addition. D electrophilic substitution. (Total for Question 18 = 1 mark) 19 The skeletal formula of an organic compound is shown below. O N This compound is A B C an amino acid. an amide. a primary amine. D a secondary amine. (Total for Question 19 = 1 mark) 20 CH 3 H C C CH 3 CH 3 n Which is the IUPAC name for the monomer which reacts to make the polymer shown above? A B C 2-methylbut-1-ene 2-methylbut-2-ene 1,2-dimethylpropene D 1,1,2-trimethylethene (Total for Question 20 = 1 mark) TOTAL FOR SECTION A = 20 MARKS *P45073RA0728* 7 Turn over

84 SECTION B Answer ALL the questions. Write your answers in the spaces provided. 21 (a) The table below shows the first and second ionization energies of nickel, copper and zinc. Element 1st ionization energy 2nd ionization energy / kj mol 1 / kj mol 1 Ni Cu Zn (i) Complete the electronic configurations for an atom of nickel and an atom of copper. (2) Ni: 1s 2 2s 2 2p 6... Cu: 1s 2 2s 2 2p 6... *(ii) The values for the first ionization energies of copper and nickel are similar, but the values of the second ionization energies are significantly different. Explain how these data give evidence for the electronic configuration of a copper atom. (2)... 8 *P45073RA0828*

85 (iii) Suggest why you might expect the third ionization energies of the three elements to increase from nickel to zinc. (b) (i) Cu + (aq) ions are not stable in solution and undergo a disproportionation reaction. Suggest an equation for this reaction, including state symbols. (ii) Suggest in what way the appearance of CuI is similar to that of ZnI 2. Give a reason for this similarity. (2) (c) Explain why zinc is not classified as a transition element. (Total for Question 21 = 9 marks) *P45073RA0928* 9 Turn over

86 22 This question is about vanadium and its ions. (a) Consider the data below. Electrode system Standard electrode potential E /V V 2+ (aq) V(s) 1.18 V 3+ (aq), V 2+ (aq) Pt 0.26 (i) Draw a labelled diagram showing how to set up a cell, using the two electrode systems in the table above, in order to measure E cell. Include standard conditions in your labelling. (3) (ii) Write an equation for the reaction in this cell. State symbols are not required. (2) (b) (i) Complete the table below with the missing standard electrode potentials. Use the table starting on page 14 of your Data Booklet. Electrode system [VO 2+ (aq) + 2H + (aq)], [V 3+ (aq) + H 2 O(l)] Pt [VO 2+ (aq) + 2H + (aq)], [VO 2+ (aq) + H 2 O(l)] Pt Standard electrode potential E /V I 2 (aq),2i (aq) Pt [2H + (aq) + O 2 (g)], [H 2 O 2 (aq)] Pt *P45073RA01028*

87 (ii) The colours of the different oxidation states of vanadium are shown below. Oxidation state Colour +5 yellow +4 blue +3 green +2 violet For each of the following experiments, A and B, calculate the E value for the proposed reaction. Use your answers to predict whether or not a reaction occurs in each case. Give the formula of the vanadium product formed where a reaction occurs and give one observation you would make in each experiment. (6) Experiment A: Hydrogen peroxide is added to an aqueous solution containing VO 2+ ions. Experiment B: An aqueous solution of potassium iodide is added to an aqueous solution containing VO 2+ ions. *P45073RA01128* 11 Turn over

88 (c) An experiment was carried out to determine the percentage purity of a sample of ammonium vanadate(v), NH 4 VO 3. An impure sample of ammonium vanadate(v) with mass g was dissolved in dilute sulfuric acid. This produced a solution containing VO 2 + ions. Excess zinc powder was added to the solution, and this reduced the VO 2 + ions to V 2 + ions. The solution containing V 2 + ions was titrated with potassium manganate(vii) of concentration mol dm 3. The manganate(vii) ions oxidized the V 2 + back to VO 2+. The volume of potassium manganate(vii) required was cm 3. (i) The manganate(vii) ions react as shown: MnO 4 + 8H + + 5e Mn H 2 O Show, by writing the appropriate half equation or otherwise, that 5 mol V 2 + react with 3 mol MnO 4. (ii) Calculate the number of moles of manganate(vii) ions used in the titration. 12 *P45073RA01228*

89 (iii) Calculate the number of moles of VO 2+ in the original solution, and hence the percentage purity of the sample of NH 4 VO 3. Give your answer to three significant figures. Molar mass of NH 4 VO 3 = g mol 1. (3) (Total for Question 22 = 17 marks) *P45073RA01328* 13 Turn over

90 23 Benzene is sometimes represented as Structure X, shown below, called a Kekulé structure after the chemist who suggested it. Structure X (a) What structural feature of benzene shows that Structure X is not an accurate representation? (b) The enthalpy changes for the formation of cyclohexane from cyclohexene and from the actual structure of benzene are given below. + H 2 H = 118 kj mol 1 + 3H 2 H = 205 kj mol 1 (i) Use the necessary data to estimate the enthalpy change for the theoretical conversion of Structure X to cyclohexane. 14 *P45073RA01428*

91 (ii) On the enthalpy level diagram below, draw labelled horizontal lines to show the relative enthalpies of the actual structure of benzene, Structure X and cyclohexane. Add an arrow to show the enthalpy change from Structure X to benzene and calculate the value of this enthalpy change in kj mol 1. Write this value next to your arrow. (2) Enthalpy *(iii) Explain the difference in the arrangement of the electrons between benzene and Structure X. (2) *P45073RA01528* 15 Turn over

92 (c) Benzene reacts with bromine in the presence of a catalyst of iron(iii) bromide. Write a mechanism for the reaction of benzene with bromine to form bromobenzene. Include an equation to show the involvement of the catalyst. (4) 16 *P45073RA01628*

93 (d) (i) State two observations which would be made when phenol reacts with bromine water. (2) (ii) Write the equation for this reaction showing the structure of the organic product. (2) *(iii) Explain why phenol can react with either bromine or with bromine water without a catalyst. (2) (Total for Question 23 = 16 marks) *P45073RA01728* 17 Turn over

94 24 Benzene can be converted to phenylamine, C 6 H 5 NH 2, in two steps. Step 1 Step 2 C 6 H 6 C 6 H 5 NO 2 C 6 H 5 NH 2 (a) (i) Name the two reagents needed in Step 1. (ii) Suggest why the temperature should not be allowed to go above 55 C in Step 1. (iii) Identify the two reagents used to carry out the reduction in Step 2. (b) Some reactions of phenylamine are shown below. Substance A B + Organic Substance C HCl(aq) CH 3 COCl C 6 H 5 NH 2 Cu 2+ (aq) Reagents G and H Substance D C 6 H 5 N 2+ Cl Substance E C 6 H 5 N=NC 6 H 2 (CH 3 ) 2 NH 2 Substance F 18 *P45073RA01828*

95 (i) Give the formula of Substance A. (ii) Draw the displayed formula of the organic Substance C. You need not display the benzene ring. (iii) Substances D and F are both brightly coloured but for different reasons. Classify Substances D and F. (2) Substance D... Substance F... (iv) Name Substance E. (v) What two Substances, G and H, are required in the conversion of phenylamine to Substance E? (vi) Suggest the structural formula of the substance which reacts with Substance E to form Substance F. (Total for Question 24 = 10 marks) TOTAL FOR SECTION B = 52 MARKS *P45073RA01928* 19 Turn over

96 SECTION C Answer ALL the questions. Write your answers in the spaces provided. 25 Read the passage below carefully and answer the questions which follow. The general formula of most naturally occurring amino acids can be written RCH(NH 2 )COOH, though in some amino acids, such as proline, the nitrogen atom is part of a five-membered ring. Amino acids are water soluble, though the extent of their solubility varies. All but one of the naturally occurring amino acids show optical activity. The formula of the R group for some naturally occurring amino acids is shown below. Amino acid serine Formula of R group CH 2 OH lysine (CH 2 ) 4 NH 2 phenylalanine CH 2 C 6 H 5 leucine CH 2 CH(CH 3 ) 2 iso-leucine CH(CH 3 )CH 2 CH 3 alanine CH 3 Mixtures of amino acids can be separated by electrophoresis. This method depends on amino acids moving different distances through paper or gel when an electric field is applied. They can also be separated by chromatography. Ninhydrin, shown below, is the chemical which is used to locate the position of the amino acids on chromatograms. O OH OH Ninhydrin detects ammonia and primary and secondary amines. When it reacts with primary amines, a deep blue or purple colour is produced in a complex series of reactions. With proline, a yellow compound forms. Ninhydrin is widely used to detect fingerprints. Sweat secretions from ridges on the finger contain dipeptides and proteins. These are left on porous surfaces such as paper, and react with ninhydrin. When ninhydrin reacts with amino acids, carbon dioxide is released from the carboxylic acid group. Archaeologists have used this reaction to release the carbon from proteins in ancient bones, and, by comparing the proportions of carbon and nitrogen in the remains, they have obtained evidence for the diets of these animals. O 20 *P45073RA02028*

97 (a) (i) At a ph of 5.68, serine exists as a zwitterion. Draw the formula of serine at this ph. *(ii) At ph 5.68, serine and lysine can be separated by electrophoresis. By considering the structures of the amino acids at this ph, suggest why this separation occurs. (2) *(b) Serine is very soluble in water, whilst phenylalanine is much less soluble. Explain the difference, disregarding any effect of zwitterion formation. (2) (c) The naturally occurring amino acid which does not show optical activity is not shown in the table. Give the formula of the R group for this acid. *P45073RA02128* 21 Turn over

98 (d) The optical activity of equimolar solutions of naturally occurring samples of leucine and iso-leucine can be measured in an experiment using plane-polarized light. (i) What measurement is made to show the optical activity of amino acids? (ii) By considering the structures of iso-leucine and leucine, explain why iso-leucine has more stereoisomers than leucine. Amino acid Formula of R group leucine CH 2 CH(CH 3 ) 2 iso-leucine CH(CH 3 )CH 2 CH 3 (e) The amino acid proline, shown below, does not contain a primary amine group, but it can still form peptide bonds. O OH NH Draw the structure of the dipeptide formed when the carboxylic acid group of alanine reacts with proline. Circle the peptide group on your drawing. (2) 22 *P45073RA02228*

99 (f) The first steps of the reaction of ninhydrin with alanine can be summarised in the equation shown below. O O OH OH + CH 3 CH(NH 2 )COOH NH 2 + CO 2 + H 2 O + Z O O Y (i) By balancing the equation, suggest the structural formula of the product Z. (ii) In the final stage, Y reacts with another molecule of ninhydrin to form a dye, Q, shown below. O O N O O What is the molecular formula of Q? *P45073RA02328* 23 Turn over

100 (iii) On combustion, g of Q produces g carbon dioxide, g water and g nitrogen. Use these data to calculate the percentage composition by mass of Q, and hence its empirical formula. Show whether your answer is consistent with the molecular formula of Q. (4) (iv) Evidence for the structure of Q is obtained from data in its mass spectrum, and the number of peaks in its low resolution nmr spectrum. Suggest one piece of evidence from each type of spectroscopy which would support the structure shown in (f)(ii). Give data where appropriate. (2) (Total for Question 25 = 18 marks) TOTAL FOR SECTION C = 18 MARKS TOTAL FOR PAPER = 90 MARKS 24 *P45073RA02428*

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105 Mark Scheme (Results) Summer 2015 GCE Chemistry (6CH01/01) The Core Principles of Chemistry

106 Edexcel and BTEC Qualifications Edexcel and BTEC qualifications come from Pearson, the world s leading learning company. We provide a wide range of qualifications including academic, vocational, occupational and specific programmes for employers. For further information, please visit our website at Our website subject pages hold useful resources, support material and live feeds from our subject advisors giving you access to a portal of information. If you have any subject specific questions about this specification that require the help of a subject specialist, you may find our Ask The Expert service helpful. Pearson: helping people progress, everywhere Our aim is to help everyone progress in their lives through education. We believe in every kind of learning, for all kinds of people, wherever they are in the world. We ve been involved in education for over 150 years, and by working across 70 countries, in 100 languages, we have built an international reputation for our commitment to high standards and raising achievement through innovation in education. Find out more about how we can help you and your students at: Summer 2015 Publications Code US041075* All the material in this publication is copyright Pearson Education Ltd 2015

107

108 General Marking Guidance All candidates must receive the same treatment. Examiners must mark the first candidate in exactly the same way as they mark the last. Mark schemes should be applied positively. Candidates must be rewarded for what they have shown they can do rather than penalised for omissions. Examiners should mark according to the mark scheme not according to their perception of where the grade boundaries may lie. There is no ceiling on achievement. All marks on the mark scheme should be used appropriately. All the marks on the mark scheme are designed to be awarded. Examiners should always award full marks if deserved, i.e. if the answer matches the mark scheme. Examiners should also be prepared to award zero marks if the candidate s response is not worthy of credit according to the mark scheme. Where some judgement is required, mark schemes will provide the principles by which marks will be awarded and exemplification may be limited. When examiners are in doubt regarding the application of the mark scheme to a candidate s response, the team leader must be consulted. Crossed out work should be marked UNLESS the candidate has replaced it with an alternative response. Mark schemes will indicate within the table where, and which strands of QWC, are being assessed. The strands are as follows: i) ensure that text is legible and that spelling, punctuation and grammar are accurate so that meaning is clear ii) select and use a form and style of writing appropriate to purpose and to complex subject matter iii) organise information clearly and coherently, using specialist vocabulary when appropriate

109 Section A (multiple choice) Question Correct Answer Reject Mark 1 B 1 Question Correct Answer Reject Mark 2 C 1 Question Correct Answer Reject Mark 3 D 1 Question Correct Answer Reject Mark 4 C 1 Question Correct Answer Reject Mark 5 B 1 Question Correct Answer Reject Mark 6(a) C 1 Question Correct Answer Reject Mark 6(b) A 1 Question Correct Answer Reject Mark 6(c) A 1 Question Correct Answer Reject Mark 7(a) C 1 Question Correct Answer Reject Mark 7(b) B 1 Question Correct Answer Reject Mark 8 D 1 Question Correct Answer Reject Mark 9 D 1

110 Question Correct Answer Reject Mark 10 B 1 Question Correct Answer Reject Mark 11 A 1 Question Correct Answer Reject Mark 12 D 1 Question Correct Answer Reject Mark 13 B 1 Question Correct Answer Reject Mark 14(a) D 1 Question Correct Answer Reject Mark 14(b) B 1 Question Correct Answer Reject Mark 15 A 1 Question Correct Answer Reject Mark 16 A 1 TOTAL FOR SECTION A = 20 MARKS

111 Section B Question 17(a) Acceptable Answers Reject Mark (Atoms/elements/isotopes with) the same number of protons (and electrons) and different numbers of neutrons 1 ALLOW answers in terms of bromine isotopes, 35 protons and 44 or 46 neutrons. IGNORE different number of nucleons IGNORE same atomic number but different mass number Question 17(b)(i) Acceptable Answers Reject Mark (High energy) electrons are fired at/ Electrons bombard/use of an electron gun Magnetic field (0) 2 (result in) loss of electron/electrons (thus forming an ion) This can be shown in an equation X + e X + + 2e OR X X + + e Forms an anion Stand alone marks Question Acceptable Answers Reject Mark 17(b)(ii) Magnet/Magnetic field/electromagnet Electric field Magnetic shield Magnetic radiation 1 Question Acceptable Answers Reject Mark 17(b)(iii) Particles (of gas/air) will interfere with the movement of the ions/collide with the ions/deflect ions Atoms for ions 1 OR Additional peaks will be detected/peaks at incorrect m/e IGNORE references to chemical reactions

112 Question Acceptable Answers Reject Mark 17(c) Marking point 1 Twin peaks of about the same height at 79 4 and 81 Marking point 2 Twin peaks of about the same height at 158 and 162 Marking point 3 Peak at 160 Marking point 4 Peak at 160 approximately twice the height of the peaks at 158 and 162 IGNORE Small peak at 80 which could be due to Br 2 2+ (79-81) In MPs 1 and 2 penalise height difference once only Question Acceptable Answers Reject Mark 17(d) ( (47 x 79) + (53x81) ) = (answer =) 80.1 Correct final answer without working scores (2) Incorrect units of mass/% No TE on incorrect expression Question Acceptable Answers Reject Mark 17(e) The (m/e) value would be halved Peak half as high 1

113 Question 17(f)(i) Acceptable Answers Reject Mark Any two from: Sample kept sealed/ tamper-proof References to medication being taken 2 Sample stored and labelled clearly Sample stored in preservative/sample tested immediately after being taken Sample kept under temperature control Monitor sample is being taken from named competitor Check that other non-banned substances do not give similar mass spectrometry result Analysis repeated (to confirm result)/ Multiple samples taken/ Sample divided into two and tested at different times/ locations Container/equipment sterile/cleaned Run a control sample/ compare to a sample without drugs Just no contamination Sampling to take place immediately after event Precautions need to be actions/activities that are carried out and not just a statement that something must or must not happen but how this is ensured or prevented There will likely be other suggestions in addition to those given above which can be given credit if they are reasonable actions

114 Question 17(f)(ii) Acceptable Answers Reject Mark Health concerns/depression/bursts of anger/ acts of violence/heart attack/strokes/liver damage/masculine features in women/ harmful side effects Just Fear of being banned/prosecuted Just side effects 1 Allow any suitable health concern Question 17(g) Acceptable Answers Reject Mark Any suitable use such as: Alcohol testing 1 RAM/RMM calculations/relative isotopic mass calculations/space probes/ Pharmaceutical purity/testing of new pharmaceuticals/age of rocks from Helium content/ Identification of unknown substances/ Carbon dating/radioactive dating C-12 dating TOTAL FOR QUESTION 17 = 16 MARKS

115 Question 18(a) Question 18(b) Acceptable Answers Reject Mark C n H 2n ALLOW any letter for n C 2 H 2n C n H 2n+2 Acceptable Answers Reject Mark Either one of the following options: 1 3 CH 2 CH 2 + Br 2 CH 2 BrCH 2 Br 1,2-dibromoethane OR CH 3 CHCH 2 + Br 2 CH 3 CHBrCH 2 Br 1,2-dibromopropane Marking Point 1 Correct reactant ethene or propene Marking Point 2 Correct product from the number of carbon atoms in the reactant Marking Point 3 Correct name from the number of carbon atoms in the reactant IGNORE punctuation on product ALLOW displayed/ skeletal formulae Penalise molecular formula of product only No TE on name if product incorrect

116 Question 18(c)(i) Acceptable Answers Reject Mark (Error 1) the dipole on the chlorine molecule should be the other way round 3 (Error 2) the arrow should be going from the double bond (to the chlorine)/electrons move from the double bond to the chlorine (Error 3) the chlorine should have a negative charge (and a lone pair) Chlorine molecule Question 18(c)(ii) Acceptable Answers Reject Mark Because tertiary carbocation is more stable (than a primary carbocation) Just Secondary carbocation 1 OR the positive carbon has more positivelyinductive/ electron-releasing alkyl groups (to help stabilization than the other carbon of the double bond) IGNORE references to carbon only having three bonds or being electron deficient Question 18(d) Acceptable Answers Reject Mark 2 OR

117 Question 18(e) Acceptable Answers Reject Mark Same molecular formula/same number of atoms/same amount of each element 1 but different (Structural) arrangement (of atoms)/ structure/ structural formulae/ displayed formulae/ skeletal formulae in space Question Acceptable Answers Reject Mark 18(f)(i) Ultraviolet (radiation)/ UV (radiation) / (Sun) light High temperature 1 Question 18(f)(ii) Acceptable Answers Reject Mark Cl-Cl 2Cl OR Cl-Cl Cl + Cl 2 Correct use of curly half / fish-hook arrows Curly half arrows can start from anywhere on the bond and extend beyond the Cl The half arrows can be above or below the bond or a combination of the two.

118 Question 18(f)(iii) Acceptable Answers Reject Mark (First propagation step) C 4 H 8 + Cl HCl + C 4 H 7 (Second propagation step) C 4 H 7 + Cl 2 C 4 H 7 Cl + Cl The position of is not essential Reference to H/ H scores (0) 2 Penalise lack of once only Question 18(f)(iv) Acceptable Answers Reject Mark Homolytic/ homolytic fission/ homolytic bond fission 1 Question Acceptable Answers Reject Mark 18(f)(v) Marking point 1 Two free radicals are combining/reacting with 2 each other/suitable termination equation Marking point 2 The product is a stable species/no free radicals produced/ The product is not a free radical/ Concentration of free radicals decreases / lowers the number of radicals Question 18(g) Acceptable Answers Reject Mark Further substitution/polysubstitution can occur 1 OR Other products such as C 4 H 6 Cl 2 / C 4 H 5 Cl 3 COMMENT: ALLOW Forms C 4 Cl 8 (TOTAL FOR QUESTION 18 =20 MARKS)

119 Question 19(a) Acceptable Answers Reject Mark 1 Drawing must have at least 1 circle around each chlorine atom OR Random dots to indicate electron density around both chlorine atoms and a concentrated area between the atoms Question 19(b) Acceptable Answers Reject Mark (Electrostatic) attraction between oppositely charged ions 1 IGNORE comments on the formation of ions

120 Question Acceptable Answers Reject Mark 19(c) Marking point 1 Either 3 Diagram of U-tube / beaker with electrodes and sodium chloride solution Sodium electrode OR Diagram of microscope slide with electrodes attached and either filter paper soaked in sodium chloride solution or dampened/wet filter paper on the top of the slide with the sample added (in the centre) Marking point 2 Suitable circuit If electrodes labelled ± or named they must be consistent with the cell For example the following would not score this marking point: Marking point 3 Ammeter/ light bulb showing conductivity OR Chlorine (gas) evolved/ Test for chlorine/hydrogen (gas) evolved/test for hydrogen Sodium formed ALLOW any other reasonable electrolysis apparatus that would work to show ionic bonding. For MP3 if the electrode at which the gas is

121 evolved is stated then it must have the correct sign or charge, although it is not necessary to name or give a sign for the electrode, ie chlorine at the electrode with a positive sign and hydrogen at the electrode with a negative sign. Use of other ionic compounds can only score MP2 Question 19(d)(i) Acceptable Answers Reject Mark Correct dot and cross diagram with charge 1 Example XX XX Cl X XX ALLOW all dots or all crosses IGNORE any sodium dot and cross diagram Question Acceptable Answers Reject Mark 19(d)(ii) (Isoelectronic example) S 2- /S -2 /P 3- /P -3 Si 4- /K + /Ca 2+ /Ar 1 Question Acceptable Answers Reject Mark 19(e) Marking point 1 Sodium conducts when solid (and Sodium in solution/dissolved 3 liquid/molten) Marking point 2 Sodium chloride conducts when molten (and in solution but not as a solid) Marking point 3 Charge carriers in sodium are (delocalised) electrons but ions in sodium chloride OR Conductivity in sodium due to the movement of (delocalised) electrons but the movement of ions in sodium chloride (TOTAL FOR QUESTION 19 = 10 MARKS)

122 Question 20(a) Acceptable Answers Reject Mark (50 x 4.18 x 15.5 =) (J) 1 IGNORE any sign given ALLOW kj (units are essential for this answer) Question Acceptable Answers Reject Mark 20(b) ( =) (mol) 2 ( H = = ) 124 kj mol -1 + sign OR ( =) (mol) ( H = = ) 125 kj mol -1 ALLOW the use of CaO = 56 = ( kj mol -1 ) 124 kj mol -1 ALLOW TE from answer to (a)

123 Question 20(c)(i) Acceptable Answers Reject Mark Any three reasons from: Incomplete reaction 3 Heat/energy loss (to the surroundings / to the apparatus)/ Lack of lid/no lid/ heat capacity of the cup not taken into account/heat capacity of the cup is not zero Just heat lost to the thermometer Inaccuracy of thermometer/temperature readings Impure CaO/Absorbed moisture from the air Heat capacity is not 4.18/ the mass of solution is not 50 g/ density of solution is not 1 g cm -3 IGNORE non-standard conditions/ stirring/human error/incomplete transfer of solid Question Acceptable Answers Reject Mark 20(c)(ii) Marking point 1 3 (Q=(250 x 4.18 x 25) = 26125(J) OR ( =) (kj) Marking point 2 (n = =) (mol) Marking point 3 Mass = ( x 56.1 =) = 7.45 (g) 7.5 ALLOW ( x 56 =) = 7.43 (g) Correct answer alone scores 3 marks

124 Question Acceptable Answers Reject Mark 20(d)(i) Marking point 1 Arrow downwards from CaCO 3 to the box, with 4 2HCl((aq)) alongside Marking point 2 Correct entities and states in box CaCl 2 (aq) + H 2 O(l) + CO 2 (g) Marking point 3 Correct use of Hess Law ( H = H CaCO3 - H CaO ) e.g = Marking point 4 H = +178( kj mol -1 ) Question Acceptable Answers Reject Mark 20(d)(ii) Products on line below CaCO 3 (s) with both 1 arrows going down from CaCO 3 and CaO Example ALLOW the word products for formulae (Total for Question 20 = 14 marks) TOTAL FOR SECTION B = 60 MARKS TOTAL FOR PAPER = 80 MARKS

125 Pearson Education Limited. Registered company number with its registered office at 80 Strand, London, WC2R 0RL, United Kingdom

126 Mark Scheme (Results) Summer 2015 GCE Chemistry (6CH02/01)

127 Edexcel and BTEC Qualifications Edexcel and BTEC qualifications come from Pearson, the world s leading learning company. We provide a wide range of qualifications including academic, vocational, occupational and specific programmes for employers. For further information, please visit our website at Our website subject pages hold useful resources, support material and live feeds from our subject advisors giving you access to a portal of information. If you have any subject specific questions about this specification that require the help of a subject specialist, you may find our Ask The Expert service helpful. Pearson: helping people progress, everywhere Our aim is to help everyone progress in their lives through education. We believe in every kind of learning, for all kinds of people, wherever they are in the world. We ve been involved in education for over 150 years, and by working across 70 countries, in 100 languages, we have built an international reputation for our commitment to high standards and raising achievement through innovation in education. Find out more about how we can help you and your students at: Summer 2015 Publications Code US041078* All the material in this publication is copyright Pearson Education Ltd 2015

128 General Marking Guidance All candidates must receive the same treatment. Examiners must mark the first candidate in exactly the same way as they mark the last. Mark schemes should be applied positively. Candidates must be rewarded for what they have shown they can do rather than penalised for omissions. Examiners should mark according to the mark scheme not according to their perception of where the grade boundaries may lie. There is no ceiling on achievement. All marks on the mark scheme should be used appropriately. All the marks on the mark scheme are designed to be awarded. Examiners should always award full marks if deserved, i.e. if the answer matches the mark scheme. Examiners should also be prepared to award zero marks if the candidate s response is not worthy of credit according to the mark scheme. Where some judgement is required, mark schemes will provide the principles by which marks will be awarded and exemplification may be limited. When examiners are in doubt regarding the application of the mark scheme to a candidate s response, the team leader must be consulted. Crossed out work should be marked UNLESS the candidate has replaced it with an alternative response. Mark schemes will indicate within the table where, and which strands of QWC, are being assessed. The strands are as follows: i) ensure that text is legible and that spelling, punctuation and grammar are accurate so that meaning is clear ii) select and use a form and style of writing appropriate to purpose and to complex subject matter iii) organise information clearly and coherently, using specialist vocabulary when appropriate

129 Using the Mark Scheme Examiners should look for qualities to reward rather than faults to penalise. This does NOT mean giving credit for incorrect or inadequate answers, but it does mean allowing candidates to be rewarded for answers showing correct application of principles and knowledge. Examiners should therefore read carefully and consider every response: even if it is not what is expected it may be worthy of credit. The mark scheme gives examiners: an idea of the types of response expected how individual marks are to be awarded the total mark for each question examples of responses that should NOT receive credit. / means that the responses are alternatives and either answer should receive full credit. ( ) means that a phrase/word is not essential for the award of the mark, but helps the examiner to get the sense of the expected answer. Phrases/words in bold indicate that the meaning of the phrase or the actual word is essential to the answer. ecf/te/cq (error carried forward) means that a wrong answer given in an earlier part of a question is used correctly in answer to a later part of the same question. Candidates must make their meaning clear to the examiner to gain the mark. Make sure that the answer makes sense. Do not give credit for correct words/phrases which are put together in a meaningless manner. Answers must be in the correct context. Quality of Written Communication Questions which involve the writing of continuous prose will expect candidates to: write legibly, with accurate use of spelling, grammar and punctuation in order to make the meaning clear select and use a form and style of writing appropriate to purpose and to complex subject matter organise information clearly and coherently, using specialist vocabulary when appropriate. Full marks will be awarded if the candidate has demonstrated the above abilities. Questions where QWC is likely to be particularly important are indicated (QWC) in the mark scheme, but this does not preclude others.

130 Section A (multiple choice) Question Correct Answer Mark 1 D 1 Question Correct Answer Mark 2 B 1 Question Correct Answer Mark 3 C 1 Question Correct Answer Mark 4 C 1 Question Correct Answer Mark 5 B 1 Question Correct Answer Mark 6 D 1 Question Correct Answer Mark 7 D 1 Question Correct Answer Mark 8 A 1 Question Correct Answer Mark 9 B 1 Question Correct Answer Mark 10(a) B 1 (b) D 1 (c) A 1 (d) D 1 Question Correct Answer Mark 11 D 1 Question Correct Answer Mark 12 A 1

131 Question Correct Answer Mark 13 C 1 Question Correct Answer Mark 14 C 1 Question Correct Answer Mark 15 D 1 Question Correct Answer Mark 16 A 1 Question Correct Answer Mark 17 C 1

132 Section B Question Acceptable Answers Reject Mark 18 (a)(i) Ethanol dissolves silver nitrate / silver ions and halogenoalkanes OR Ethanol (molecule) is polar and non-polar (solvent) OR Ethanol dissolves ionic and covalent compounds Ethanol is nonpolar Just ethanol dissolves halogenoalkanes Just water does 1 not dissolve halogenoalkanes ALLOW Ethanol dissolves ionic and nonpolar compounds Ethanol dissolves both types (of compound) So that the reactants can mix miscible for dissolves IGNORE Any references to rate Just they dissolve in ethanol Question 18(a)(ii) Acceptable Answers Reject Mark To allow the temperature (of all the liquids) to equilibrate / to reach 50 C OR So that all the substances are at the same temperature ALLOW So that the temperature is constant 1 Question Acceptable Answers Reject Mark 18(a)(iii) Silver bromide 2 IGNORE Formula even if incorrect Ag + + Br AgBr TE on incorrect silver halide Non-ionic equations ALLOW Ionic equations with uncancelled ions Ag + Br as product IGNORE state symbols even if incorrect

133 Question Acceptable Answers Reject Mark 18(a)(iv) Order: iodo, bromo, chloro 2 ALLOW AgI, AgBr, AgCl OR I, Br, Cl OR Iodine, bromine, chlorine I 2, Br 2, Cl 2 C I is the weakest bond OR I is best leaving group Rate depends on the reactivity of X / X ALLOW (if MP1 awarded) Rate depends on the strength of the C X bond IGNORE Explanations of the bond strengths, even if incorrect. References to bond length and atomic radius/size ALLOW Reverse argument for MP2 Question Acceptable Answers Reject Mark 18(b)(i) nucleophilic 2 substitution Stand alone marks S N 2 alone scores one mark S N 1

134 Question Acceptable Answers Reject Mark 18(b)(ii) Some comparison is required. 1 Hydroxide ion /OH is a stronger nucleophile (than water) ALLOW OH is a better electron pair donor (than water) Concentration of hydroxide ion / OH is higher OR Hydroxide ion / OH is charged More hydroxide ion / OH in NaOH (than water) Use of NaOH/OH for OH Just NaOH/alkali forms OH more readily IGNORE OH is more basic / alkaline Alkali is a stronger nucleophile OH is more reactive ALLOW Reverse argument

135 Question 18 (b)(iii) Acceptable Answers Reject Mark Penalise omission of charge on hydroxide ion once only (in MP2) 3 First mark C 3 H 7 C 3 H 7 Both curly arrows First curly arrow from any part of the hydroxide ion (or the charge) to the carbon atom Second curly arrow from the C Br bond to the bromine atom or just beyond Second mark Lone pair on oxygen of OH {HO:} Third mark Partial charge on C Br bond { C δ+ Br δ } OH with no / partial charge C + Br ALLOW Correct S N 1 mechanism for full marks Curly arrow from hydroxide group from any part of the group including the charge. IGNORE transition state (even if incorrect) products (even if incorrect)

136 Question Acceptable Answers Reject Mark 18(b)(iv) PCl 5 : misty /steamy /white fumes/gas IGNORE Tests on product (e.g. turns blue smoke Just fumes / effervescence 3 litmus red) K 2 Cr 2 O 7 : orange solution turns green ALLOW Orange to blue K 2 Cr 2 O 7 preferred because PCl 5 reacts with water (as well as alcohols) ALLOW K 2 Cr 2 O 7 preferred because PCl 5 reacts with alkali / OH /OH PCl 5 reacts with carboxylic acids IGNORE References to primary, secondary and tertiary alcohols Question Acceptable Answers Reject Mark 18(c) Skeletal formula Classification 3 Just the classificat Primary/1 o ions Secondary/2 o Tertiary/3 o Look at the structural formulae first: three structures correct scores 2 marks. two structures correct scores 1 If all three structures correct (any format), then all three classifications correct scores 1 Penalise displayed, partially displayed or structural formulae once only IGNORE Bond angles and names Total for Question 18 = 18 marks

137 Question Acceptable Answers Reject Mark 19(a)(i) Add hydrochloric acid / HCl(aq) / nitric acid / HNO 3 (aq) Just acid OR heating the 2 ALLOW Just acid only if a suitable acid is given in equation one Sulfuric acid / H 2 SO 4 ((aq)) or HCl carbonate IGNORE conc Gas / carbon dioxide / CO 2 evolved turns lime water milky / cloudy / produces a white precipitate MP2 is a stand alone mark but there must be some indication that a gas is being tested Question 19(a)(ii) Acceptable Answers Reject Mark ALLOW H 2 CO 3 (aq) for H 2 O(l) + CO 2 (g) 3 BaCO 3 (s) + 2HCl(aq) BaCl 2 (aq) + H 2 O(l) + CO 2 (g) OR BaCO 3 (s) + 2HNO 3 (aq) Ba(NO 3 ) 2 (aq) + H 2 O(l) + CO 2 (g) OR CO 2 3 (s) + 2H + (aq) H 2 O(l) + CO 2 (g) ALLOW BaCO 3 (s) + H 2 SO 4 (aq) BaSO 4 (s/aq) + H 2 O(l) + CO 2 (g) OR BaCO 3 (s) BaO(s) + CO 2 (g) Ca(OH) 2 (aq) + CO 2 (g) CaCO 3 (s) + H 2 O(l) All state symbols in both equations correct ALLOW State symbols mark if first equation not balanced but ALL species are correct. No TE on other equations

138 Question 19(b)(i) Acceptable Answers Reject Mark MP1 and MP2 Dip (clean) nichrome / platinum wire ALLOW loop / rod for wire OR Silica rod Nickel / chrome / chromium spatula 3 in hydrochloric acid / HCl(aq) ALLOW any mention of HCl(aq) e.g. cleaning or mixing solid and acid HCl for HCl(aq) Other acids ALLOW (for MP1 and MP2) (Wooden) splint Soaked in distilled / deionised water MP3 then dipped in solid and placed in (hot / roaring / blue-cone) (Bunsen) flame ALLOW On / over / under / above for in just water IGNORE inoculating / flame-test (wire) Question Acceptable Answers Reject Mark 19(b)(ii) A = Mg 2+ 2 B = Ca 2+ Penalise omission of 2+ only once Correct ions with correct charge but the wrong way round scores 1 mark Correct ions with incorrect / no charge scores 1 IGNORE Names / compounds

139 Question Acceptable Answers Reject Mark 19(b)*(iii) Read the whole answer before 3 awarding marks. If no mention of electrons only MP3 may be awarded. Electrons promoted to higher energy level (by thermal energy / heat from (Bunsen) flame) (Promoted) electrons fall / drop / relax to lower energy level / orbital / shell / subshell OR Electrons return to ground state Emitting radiation / light / photons (in the visible region) Just electrons promoted/ excited Just energy lost Just energy given out IGNORE Colour Question Acceptable Answers Reject Mark 19(b)(iv) Emitted radiation is not in the visible 1 region (of the spectrum) ALLOW Emitted radiation is in IR / UV

140 Question 19(c) Acceptable Answers Reject Mark As group is descended... 3 First mark (metal ion size) (Metal) ion radius increases / has more (electron) shells (but charge remains the same) OR Charge density of metal ion decreases ALLOW (Metal) atomic radius increases / has more (electron) shells Second mark (polarizing species) Polarizing (ALLOW distorting) power of cation / metal ion decreases Third mark (polarized species) Polarization / distortion of (electron cloud of) carbonate ion /anion decreases Just metal Just ion Just ion or bond ALLOW C O / C O for carbonate ion (so carbonate more stable to heat) ALLOW reverse argument for ascent of the group. Total for Question 19 = 17 marks

141 Question 20(a) Acceptable Answers Reject Mark Methane undergoes more complete combustion / produces less CO OR Burning methane emits no (allow less) soot / carbon particles / particulates OR Burning methane emits no (allow less) sulfur / sulfur oxides OR Sulfur compounds are much more easily removed from methane OR Methane produces less CO 2 per unit of energy than coal 1 ALLOW Any of these points reversed for coal IGNORE less CO 2 / greenhouse gases carbon footprint and emissions Question 20(b) Acceptable Answers Reject Mark Any mention of the ozone layer scores zero 2 (A greenhouse gas) absorbs & reemits / absorbs / traps / reflects IR (radiation) / heat (re-radiating) from the Earth UV absorbed etc Absorbs from the sun ALLOW Back to the Earth

142 Question 20(c) Acceptable Answers Reject Mark Methane (molecule) absorbs IR radiation more effectively (because it has more IR active vibrations) OR Methane has a longer life in the atmosphere C H more polar than C=O 1 ALLOW Methane (molecule) absorbs more (IR) radiation OR Methane has more (vibrating polar) bonds OR Methane has 4 (polar) bonds (rather than 2) Total for Question 20 = 4 marks Total for Section B = 39 marks

143 Section C Question Acceptable Answers Reject Mark 21(a) Chlorine / Cl 2 / same species / element / atom is oxidized and reduced (in the 3 same reaction) Chlorine oxidized from 0 to +1 in HOCl /OCl /chlorate(i) Chlorine reduced from 0 to 1 in HCl / Cl / chloride If oxidized and /or reduced omitted or the wrong way round, max 1 (out of final 2 marks) Question 21(b)(i) Acceptable Answers Reject Mark X X 2 X H O O Cl X X Two bonding pairs Five non-bonding electron pairs IGNORE Lines representing bonds X X ALLOW Bonding pairs on the same horizontal line Different symbols for electrons max 1

144 Question 21(b)*(ii) Acceptable Answers Reject Mark No TE on incorrect structure in b(i) Penalise omission of pairs once only 5 First mark Bond angle = ALLOW Second mark 2 bond pairs and 2 lone pairs (of electrons in valence shell of the oxygen atom) Third & fourth marks (stand alone) (valence) electron pairs at minimum repulsion ALLOW maximum separation / distance apart Bonds for electron pairs lone pair repulsion > bond pair repulsion Fifth mark So tetrahedral bond angle reduced ALLOW 109 / / (angle) reduced

145 Question Acceptable Answers Reject Mark 21c(i) Amount of S 2 O 2 3 = 9.65 x * 3 (= x 10 5 mol) Amount of Cl 2 ( in 1 dm 3 ) = 0.5 x * = 0.5 x 9.65 x ** (= x 10 5 mol) Mass of Cl 2 (in 1 dm 3 ) = 71 x 1000 x ** = (mg dm 3 ) (so within limits) Incorrect units ALLOW x10-3 g dm -3 and so within limits An answer lower than 1 or higher than 2 mg dm 3 only scores a TE mark if there is a comment relating to the limits Correct answer with no working scores 1 Ignore SF except 1 SF Note If 0.5 omitted in MP2 and 35.5 used in MP3 then final answer is numerically correct; this scores only MP1 Question 21c(ii) Acceptable Answers Reject Mark Concentration of chlorine might be different in different parts of the pool / at different times OR Sample size small in relation to pool volume 1 IGNORE Just sample size is small References to experimental uncertainty Question Acceptable Answers Reject Mark 21d(i) 2HOCl 2HCl + O 2 OR HOCl HCl + ½O 2 OR Other multiples 1 ALLOW HClO or H + + ClO for HOCl

146 Question Acceptable Answers Reject Mark 21d(ii) London forces / dispersion forces / induced dipole- induced dipole attractions (ALLOW van der Waals / vdw forces) dipole-dipole forces 2 Stronger because bromine (molecule) has more electrons / electron shells ALLOW greater surface area more for stronger Question 21e(i) Acceptable Answers Reject Mark All three marks are stand alone 3 Lowering ph increases [H + ] OR Increasing ph reduces [H + ] ALLOW More/less H + IGNORE More acidic/alkaline Just repeating information from the table Lowering ph / increased [H + ] shifts equilibrium to the left (so [HOBr] increases) Increasing ph / reduced [H + ] shifts equilibrium to the right (so [OBr ] increases) Explanations must refer to equilibrium, but this may be implied Question 21e(ii) Acceptable Answers Reject Mark Alkaline solutions are irritant (to the eyes) ALLOW caustic / corrosive saponifies / burns skin / chemical burns stings eyes toxic 1 IGNORE Harmful Total for Question 21 = 21 marks Total for Section C = 21 marks

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148 Mark Scheme (Results) Summer 2015 GCE Chemistry (6CH04/01)

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150 General Marking Guidance All candidates must receive the same treatment. Examiners must mark the first candidate in exactly the same way as they mark the last. Mark schemes should be applied positively. Candidates must be rewarded for what they have shown they can do rather than penalised for omissions. Examiners should mark according to the mark scheme not according to their perception of where the grade boundaries may lie. There is no ceiling on achievement. All marks on the mark scheme should be used appropriately. All the marks on the mark scheme are designed to be awarded. Examiners should always award full marks if deserved, i.e. if the answer matches the mark scheme. Examiners should also be prepared to award zero marks if the candidate s response is not worthy of credit according to the mark scheme. Where some judgement is required, mark schemes will provide the principles by which marks will be awarded and exemplification may be limited. When examiners are in doubt regarding the application of the mark scheme to a candidate s response, the team leader must be consulted. Crossed out work should be marked UNLESS the candidate has replaced it with an alternative response. Mark schemes will indicate within the table where, and which strands of QWC, are being assessed. The strands are as follows: i) ensure that text is legible and that spelling, punctuation and grammar are accurate so that meaning is clear ii) select and use a form and style of writing appropriate to purpose and to complex subject matter iii) organise information clearly and coherently, using specialist vocabulary when appropriate

151 Section A (multiple choice) Question Correct Answer Reject Mark 1 D 1 Question Correct Answer Reject Mark 2 B 1 Question Correct Answer Reject Mark 3 C 1 Question Correct Answer Reject Mark 4 C 1 Question Correct Answer Reject Mark 5 C 1 Question Correct Answer Reject Mark 6 (a) D 1 Question Correct Answer Reject Mark 6 (b) A 1 Question Correct Answer Reject Mark 7 D 1 Question Correct Answer Reject Mark 8(a) D 1 Question Correct Answer Reject Mark 8(b) A 1 Question Correct Answer Reject Mark 9 C 1 Question Correct Answer Reject Mark 10(a) D 1

152 Question Correct Answer Reject Mark 10(b) B 1 Question Correct Answer Reject Mark 10(c) C 1 Question Correct Answer Reject Mark 11(a) D 1 Question Correct Answer Reject Mark 11(b) A 1 Question Correct Answer Reject Mark 11(c) C 1 Question Correct Answer Reject Mark 12(a) B 1 Question Correct Answer Reject Mark 12(b) A 1 Question Correct Answer Reject Mark 12(c) B 1 Total for Section A = 20 marks

153 Section B Q13 (a) PENALISE USE OF CH 3 COOH / ethanoic acid [instead of propanoic acid] once only. ALLOW NaOH for KOH, however. Question 13 (a)(i) Correct Answer Reject Mark Q13 (a) PENALISE USE OF CH 3 COOH / ethanoic acid [instead of propanoic acid] once only. ALLOW NaOH for KOH, however. 3 1st mark: Identification of buffer Any mention of buffer / buffering (region) IGNORE references to shape / gradient of graph 2nd mark: Identification of species present responsible for buffering action (Both) propanoic acid and propanoate (ions) present OR (Both) propanoic acid and potassium propanoate present OR (Both) a weak acid and its salt/conjugate base are present OR (Both) CH 3 CH 2 COOH and CH 3 CH 2 COO present OR (Both) HA and A are present Can be awarded from an equation

154 3rd mark: Two routes for this mark: 1st route: For how these species were formed OR alternatively 2nd route: For mention of how this buffer works, on small additions of OH 1st ROUTE to 3rd mark CH 3 CH 2 COOH + OH H 2 O + CH 3 CH 2 COO OR In words, excess CH 3 CH 2 COOH is left / some CH 3 CH 2 COOH has reacted with potassium hydroxide / KOH / OH (forming propanoate ions) 2nd ROUTE buffering action On addition of OH (in small quantities) H + ions react with (the added) OH and (the equilibrium) CH 3 CH 2 COOH CH 3 CH 2 COO + H + shifts to the right OR (the reservoir of undissociated) CH 3 CH 2 COOH molecules react with (the added) OH NOTE: For the 2nd route OR mark here, this statement/equation must be in the context of buffering action IGNORE References to buffering action on addition of H + ions (not relevant here)

155 Question 13 (a) (ii) Correct Answer Reject Mark 1st scoring point: Propanoate ions present (at equivalence point) OR Potassium propanoate present (at equivalence point) 3 2nd scoring point: Propanoate (ions) react with water / propanoate (ions) are hydrolysed by water / CH 3 CH 2 COO ions react with water ALLOW propanoate ions react with H + (from water) / the salt reacts with water (molecules) 3rd scoring point consequential on 2 nd scoring point being awarded: Forming hydroxide ions/ leaves excess of hydroxide ions / produces OH / forming OH / forming KOH / [OH ] > [H + ] NOTE the equation: CH 3 CH 2 COO + H 2 O OH + CH 3 CH 2 COOH OR CH 3 CH 2 COOK + H 2 O KOH + CH 3 CH 2 COOH scores ALL THREE MARKS NOTE Just weak acid strong base titration scores only

156 Question 13 (a) (iii) Correct Answer Reject Mark [FIRST, CHECK THE FINAL ANSWER IF ANSWER ph = 12(.02), award 5 marks] Moles of acid used = 25/1000 x OR moles of acid used = 6 x 10 4 (mol) 5 and Moles of alkali added = 40/1000 x OR Moles of alkali added = 1.28 x 10 3 (mol) Moles of excess alkali = 1.28 x x 10 4 OR Moles of excess alkali = 6.8 x 10 4 (mol) [OH ] = 6.8 x 10 4 /(65/1000) = (mol dm 3 ) Allow TE from incorrect moles of acid or alkali, provided the alkali moles are in excess [H + ] = 1 x / = 9.56 x (mol dm 3 ) Allow TE from incorrect moles of excess alkali or the candidate s value of [OH ]. Must use K w value here to get [H + ] ph = log 9.56 x = 12(.02) Can get M4 and M5 using ph + poh = 14 Allow TE from incorrect [H + ] for M5, but their CQ ph must > 7 IGNORE S.F. EXCEPT 1 SF

157 NOTE If fail to by dm 3, then ph = 10.8 scores 4 marks. Other answers to look for if M1 and M2 have been awarded, but division by an incorrect value for the total volume of the mixture, then each of the following would score 4 overall as shown. If by dm 3, no M3 ph = 12(.43) scores 4 marks. If by dm 3, no M3 ph = 12(.23) scores 4 marks. If by dm 3, no M3 ph = 12(.66) scores 4 marks.

158 Question Correct Answer Reject Mark 13 (b) No, as T increases eqm moves to RHS / K w increases / favours RHS / S total increases 3 So [H + ] ions increases / more H + ions [H + ] > 1 x 10 7 Hence ph < 7 / ph decreases OR reverse argument for a decrease in temperature NOTE If answer given is Yes (i.e. candidate thinks that the ph of pure water is always 7.0), then max for stating that equilibrium shifts to the right when temperature increases (since reaction is endothermic in the forward direction) NOTE If says K w decreases as T increases, then max for a completely logical CQ argument mentioning the effect on [H + ] (decreasing) and ph (increasing) (TOTAL FOR QUESTION 13 = 14 marks)

159 Question Correct Answer Reject Mark 14 (a) 1st mark: Take samples (of reaction mixture) at various times OR Using of different mixtures (e.g. in separate conical flasks) THEN: EITHER Quench (with ice) / remove the catalyst NaHCO 3 3 Titrate with acid of known concentration/standard (using a suitable indicator) OR Quench with acid NaHCO 3 Titrate with alkali of known concentration (using a suitable indicator) If no quenching, M3 can only be awarded if titrate with acid of known concentration Question 14 (b) (i) Correct Answer Reject Mark (As) rate is (directly) proportional to concentration / as [A] doubles so does rate / rate concentration / rate [A] 1 ALLOW Just straight line through origin/(0,0) IGNORE References just to a constant gradient References to just it is a straight line References to positive correlation

160 Question 14 (b) (ii) Correct Answer Reject Mark 1st mark: Rate higher than expected / rate unusually high / higher rate (for the anomalous points on the graph) 3 2nd mark: Reaction is exothermic / (heat) energy is released during the reaction 3rd mark: EITHER (So) there are more particles/collisions with energy > E a ALLOW Higher proportion of successful collisions / just more successful collisions IGNORE Just more collisions / more frequent collisions OR At higher concentrations of A, the effect of the reaction being exothermic is greater

161 Question 14 (c) (i) Correct Answer Reject Mark Increases reliability / improves validity (of the data obtained) / confirms the initial results / to check for anomalous results IGNORE References to average / precision / accuracy 1 OR To determine order w.r.t. B and X / to see the effect of B and X (on the rate) / enables order of other reagents to be determined / to determine order w.r.t. B / find overall order / determine rate equation / to calculate k Question 14 (c) (ii) Correct Answer Reject Mark 0 order w.r.t. B 5 1st order w.r.t. X Rate =k [A][X] OR Rate = k [A][X][B] 0 ALLOW TE for CQ correct rate equation on incorrect order(s) Correct reasoning using data from table to deduce the CORRECT order w.r.t. B NOTE that there must be reference to TWO relevant concentrations changing Eg (Expt 1 & 3) [A] triples, so does rate AND [B] doubles so order w.r.t. B is 0 (Expt 2 & 3) [A] x 1.5, rate x 1.5 AND [B] doubles so order w.r.t. B is 0 This mark can only be awarded if the reasoning shows that order w.r.t B is zero. Not enough just to say as [B] doubles, rate unchanged Correct reasoning using data from table to

162 deduce the CORRECT order w.r.t. X NOTE that there must be reference to TWO relevant concentrations changing E.g. (Expt 1 & 4) [A] x 4 (and [B] x 2) AND [X] 2 rate doubles so order w.r.t. X is 1 (Expt 2 & 4) [A] x 2 (and [B] x 2) AND [X] 2 rate stays the same so order w.r.t. X is 1 (Expt 3 & 4) [A] x 4/3 (and [B] stays the same) AND [X] 2 rate decreases by 2/3, so order w.r.t. X is 1 This mark can only be awarded if the reasoning shows that order w.r.t X is one. Not enough just to say as [X] doubles, rate doubles IGNORE Any justification not concluded from data in the table Working to confirm order w.r.t. A = 1 (already given in question) NOTE Correct rate equation alone scores M1, M2 and M3

163 Question 14 (c) (iii) Correct Answer Reject Mark k = rate / [A][X] = 4.2 x 10 3 (0.08 x 0.25) 2 = 0.21 dm 3 mol 1 s 1 / mol 1 dm 3 s 1 ALLOW units in any order Comment Unit mark is independent of the value Allow use of data from experiments 1, 2 & 3 Allow TE from an incorrect rate equation given in answer to Q14(c)(ii) or a new rate equation given at the start of answer to Q14(c)(iii), if of the form rate = k

164 Question Correct Answer Reject Mark 14 (d) Correct feature 3 ANY one of: First step does involve carbocation formation / carbocation is correct / two electrons taken by Br atom in C Br bond / C Br bond breaks (heterolytically) (Second step does involve) attack of hydroxide ion First order wrt the halogenoalkane / 1st order wrt 2-bromomethylpropane (S N 1) is a two-step process Curly arrows are correct Incorrect features ANY two of: Should be S N 1 (not S N 2) First step is slow Second step is fast (It is not) S N 2 C δ+ Br δ- not shown / dipole on C Br bond not shown (2) TOTAL FOR QUESTION 14 = 18 marks)

165 Question Correct Answer Reject Mark 15 (a) EITHER (consideration of kinetics) 2 Rate of reaction increases As collisions are more frequent / increases frequency of collisions / more collisions per second IGNORE Just more collisions or just more successful collisions OR (if assumes an equilibrium reaction) Yield increases / eq m shifts to RHS Since fewer moles of gas / no moles of gas / fewer molecules of gas (on RHS) MUST AWARD MARKS BY ONLY CONSIDERING ONE OF THE ROUTES CANNOT score full marks via one mark from each route if MIX UP KINETICS AND EQUILIBRIUM ARGUMENTS Eg Rate increases, so yield of product increases scores

166 Question Correct Answer 15 (b) [FIRST, CHECK THE FINAL ANSWER IF ANSWER = 3.1 (tonnes), award 3 marks] EITHER 1 tonne C 6 H 5 ONa : 180/116 tonnes C 6 H 4 (OH)(CO 2 H) 2.5 tonnes C 6 H 5 ONa : (180/116) x 2.5 (tonnes) C 6 H 4 (OH)(CO 2 H) at 100% yield (= tonnes) So actual yield = (180/116) x 2.5 x 79/100 Rejec t g Mark 3 (3.06) = 3.1 (tonnes) OR Moles C 6 H 5 ONa (= 2.5 x ) = (mol) Moles C 6 H 5 ONa (79% yield) (= x 0.79) = (mol) Mass C 6 H 5 ONa (= x 180 = g = 3.06 tonnes) = 3.1 (tonnes) to 2SF Correct answer TO 2 SF, no working (3) Can work in g (instead of tonnes) until final answer So final answer of 3.06 (tonnes) scores M1 and M2 only Award only mark for 3.07 (tonnes) without working

167 Question Correct Answer Reject Mark 15 (c) Esterification / acylation / ethanoylation ALLOW acetylation 2 OR (nucleophilic) addition-elimination BOTH words (addition and elimination) are needed for this option IGNORE Condensation CH 3 COCl / ethanoyl chloride OR (CH 3 CO) 2 O / ethanoic anhydride ALLOW CH 3 COOH / ethanoic acid (in presence of H 2 SO 4 ) Correct displayed / skeletal formulae IGNORE JUST acid anhydride / acid chloride (TOTAL FOR QUESTION 15 = 7 marks)

168 Question 16 (a) (i) Correct Answer Reject Mark 1st mark: 2 Filter (off solid) / centrifuge 2nd mark: (Fractionally) distil / evaporate ALLOW recrystallise for 2nd mark Just heat / steam distillation for 2nd mark IGNORE Any other practical steps (e.g. separating funnel) Mark the two scoring points independently, but award if filter is first mentioned after distil / evaporate / heat / steam distillation Question 16 (a) (ii) Correct Answer Reject Mark 2 First mark for all three esters Second mark for structure of propane 1,2,3-triol IGNORE Formulae written such as C 3 H 5 (OH) 3 or C 3 H 8 O 3 ALLOW CO 2 or OCO for COO for ester linkage H 3 COOCR / CH 3 OOCR Mark independently