Paper Reference. Paper Reference(s) 6256/01 Edexcel GCE Chemistry (Nuffield) Advanced Level Unit Test 6 (Synoptic)

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1 Centre No. Candidate No. Paper Reference(s) 6256/01 Edexcel GCE Chemistry (Nuffield) Advanced Level Unit Test 6 (Synoptic) Thursday 19 June 2008 Morning Time: 2 hours Materials required for examination Nil Paper Reference Surname Signature Items included with question papers Nil Initial(s) Examiner s use only Team Leader s use only Question Number Blank A calculator may be used. Centre to provide Nuffield Students Book (fourth edition) Nuffield Advanced Science Book of Data Instructions to Candidates In the boxes above, write your centre number, candidate number, your surname, initial(s) and your signature. Answer ALL questions. Write your answers in the spaces provided in this question paper. Final answers to calculations should be given to an appropriate number of significant figures. Information for Candidates The marks for individual questions and the parts of questions are shown in round brackets: e.g.. The total mark for this paper is 60. There are 16 pages in this paper. All pages are indicated. Advice to Candidates You may use the Nuffield Students Book and the Book of Data in answering this paper. The time allowed to answer this paper means that you do not have time to look up all the information you may wish to refer to in your answers. You should plan to restrict your use of the Students Book to relevant passages of background reading or for confirmation of data or equations. You will be assessed on your ability to organise and present information, ideas, descriptions and arguments clearly and logically, taking account of your use of grammar, punctuation and spelling. Your Quality of Written Communication will be assessed in this paper. To gain full marks you must explain your ideas clearly using equations and diagrams where appropriate. You are advised to show all the steps in any calculations. This publication may be reproduced only in accordance with Edexcel Limited copyright policy Edexcel Limited. Printer s Log. No. N31028A W850/R6256/ /7/7/3/4100 *N31028A0116* Total Turn over

2 Answer ALL the questions. Write your answers in the spaces provided. 1. (a) Draw a fully labelled diagram of the Born-Haber cycle that can be used to calculate the lattice energy of calcium hydride, CaH 2. Calculate the lattice energy of calcium hydride using your Born-Haber cycle. Give your answer to four significant figures. (5) 2 *N31028A0216*

3 (b) Aluminium also forms a hydride, AlH 3. Predict, with a reason, whether the theoretical and experimental values for lattice energy will be closer for aluminium hydride or for calcium hydride. (c) Suggest why the melting point of calcium hydride is greater than the melting point of both potassium hydride, KH, and hydrogen bromide, HBr. (d) (i) Calcium hydride reacts violently with water producing calcium hydroxide and hydrogen. Write an equation for the reaction of the hydride ion with water. State symbols are not required. (ii) The water in this reaction is acting in two different ways. State, giving your reasons, the two types of reaction brought about by the water. Q1 (Total 12 marks) *N31028A0316* 3 Turn over

4 2. Mixtures of amino acids can be separated by paper chromatography, and the chromatograms assist in the identification of the amino acids. Refer to the table on page 436 of the Students Book for data on amino acids. (a) Chromatography was carried out on a mixture of glycine and serine to confirm the presence of each amino acid. The solvent used was butan-1-ol/ethanoic acid/water. The results of the chromatogram were inconclusive. (i) Predict, with a reason, the appearance of this chromatogram after development with a suitable locating agent. (ii) Suggest ONE way in which the chromatography technique could be modified to give more conclusive results. (b) Other methods can be used to distinguish between samples of naturally-occurring glycine and serine. For the tests below, state the observations you would expect with each amino acid and explain your reasoning. (i) Warm each amino acid with a mixture of potassium dichromate(vi) solution and sulphuric acid. 4 *N31028A0416*

5 (ii) Place a solution of each amino acid in a polarimeter and view the polarised light. (iii) Count the number of peaks which would be produced by each amino acid in a low-resolution nmr spectrum. Explain the reason for any difference. (3) (c) Glycine and serine can be combined to form two different dipeptides. Draw a formula of ONE of these dipeptides, displaying the bonds in the link between the two amino acids. (Total 11 marks) Q2 *N31028A0516* 5 Turn over

6 3. The drug ibuprofen can be synthesised from benzene by the route shown below. H C H C H C H C CH 2 CH 2 Step A Step B Step C CH 2 CO/Pd catalyst CH 2 C=O H C OH H C CO 2 H Ibuprofen (a) Name the type and mechanism of the reaction in Step A, and suggest a suitable reagent and catalyst. Type and mechanism... Name of the reagent for Step A... Catalyst... (3) (b) Step C is a reduction. Give ONE reason why lithium tetrahydridoaluminate, LiAlH 4, is preferred to hydrogen as a reducing agent in this reaction. 6 *N31028A0616*

7 (c) A sample of the final product was analysed by combustion g was burnt in oxygen. It produced 2.78 g carbon dioxide and g water. State the molecular formula of ibuprofen and show that these results are consistent with it. (4) *N31028A0716* 7 Turn over

8 (d) Ibuprofen can be analysed by instrumental methods. The infrared spectra of ibuprofen and two other drugs, aspirin and paracetamol, not necessarily in that order, are shown opposite. H C CH 2 Ibuprofen has the formula H C CO 2 H Aspirin has the formula CO 2 H O C O OH Paracetamol has the formula H N C O (i) Explain, referring to the structure of each molecule, why infrared spectroscopy is not a good technique to distinguish aspirin from ibuprofen. QUESTION 3 CONTINUES ON PAGE 10 8 *N31028A0816*

9 Spectrum X 100 Transmittance (%) 50 Spectrum Y Wavenumber/cm Transmittance (%) 50 Spectrum Z Wavenumber/cm Transmittance (%) Wavenumber/cm 1 *N31028A0916* 9 Turn over

10 (ii) Deduce which of X, Y or Z is the infrared spectrum of paracetamol, giving a piece of evidence from the spectrum you select. (iii) Ibuprofen and aspirin can be distinguished using their mass spectra. A line at mass/charge ratio 57 occurs only in the mass spectrum of ibuprofen. Give the formula of the ion which produces this line. Suggest the mass/charge ratio of one line which occurs in the mass spectrum of aspirin but not ibuprofen, and the formula of the species which produces it. (3) Q3 (Total 14 marks) 10 *N31028A01016*

11 4. This question is about ethanedioate ions, (CO 2 ) 2. The structure of ethanedioic acid is shown below. HO O C C OH O (a) (i) The bonds between carbon and oxygen in the ethanedioate ion are all the same length. Suggest a reason for this. (ii) The value of the OCO bond angle in the ethanedioate ion is 122. Explain how this arises. (b) (i) How do ethanedioate ions act as bidentate ligands? You may include a diagram if you wish. (ii) The ethanedioate ions form an octahedral complex with Cr 3+ ions. Deduce the formula of the complex ion. *N31028A01116* 11 Turn over

12 (c) (i) Ethanedioate ions can be oxidised to carbon dioxide. The electrode potential for this oxidation can be measured using a hydrogen electrode. Complete the cell diagram for this procedure. Pt[H 2 (g)] 2H + (aq)... (ii) Ethanedioate ions reduce manganate(vii) ions to Mn 2+ ions in acid conditions, but do not reduce zinc ions. Use this information and the Book of Data to deduce maximum and minimum values for the standard electrode potential of the half-cell in which ethanedioate ions are oxidised to carbon dioxide. Maximum... Minimum... (d) A solution contained g of iron(ii) ethanedioate, FeC 2 O 4. This solution was acidified and reacted with cm 3 of a solution of mol dm 3 potassium manganate(vii), KMnO 4, in a titration. The manganate(vii) ion reacts as shown: MnO 4 (aq) + 8H + (aq) + 5e Mn 2+ (aq) + 4H 2 O(l) (i) Write half equations for the two oxidation reactions which occur in the titration. 12 *N31028A01216*

13 (ii) Calculate the number of moles of iron(ii) ethanedioate and manganate(vii) ions which react, and use the half equations to explain the ratio in which they react. (4) (iii) The reaction which occurs in the titration is autocatalysed. Describe how autocatalysis affects what you would observe as the titration is carried out. Q4 (Total 16 marks) *N31028A01316* 13 Turn over

14 5. This question is about polymerisation reactions. (a) The polymer ( CH 2 CHCl ) n is made in an addition reaction. Draw the displayed formula of the monomer used to make it, and suggest why this polymer is more rigid than polythene. (b) A polymer can be made from 2-hydroxypropanoic acid, CH(OH)CO 2 H. Draw a section of the polymer showing two monomer units. State the type of polymerisation which occurs and name the type of link between the monomers. (3) 14 *N31028A01416*

15 (c) Epoxyethane is an unstable compound made from ethene and oxygen. (i) The ring in epoxyethane is unstable and breaks open easily. Suggest a reason for this. (ii) Epoxyethane takes part in addition polymerisation. Draw a section of the polymer showing two monomer units. O H 2 C CH 2 Q5 (Total 7 marks) TOTAL FOR PAPER: 60 MARKS END *N31028A01516* 15

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