Cambridge A Level Chemistry 9701 — 2012 May/June Paper 2 · Variant 1

READ THESE INSTRUCTIONS FIRST Write your Centre number, candidate number and name on all the work you hand in. Write in dark blue or black pen. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fl uid. DO NOT WRITE IN ANY BARCODES. Answer all questions. You may lose marks if you do not show your working or if you do not use appropriate units. A Data Booklet is provided. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. CHEMISTRY 9701/21 Paper 2 Structured Questions AS Core May/June 2012 1 hour 15 minutes Candidates answer on the Question Paper. Additional Materials: Data Booklet UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS General Certifi cate of Education Advanced Subsidiary Level and Advanced Level This document consists of 11 printed pages and 1 blank page. [Turn over IB12 06_9701_21/3RP © UCLES 2012 *1182281800* For Examiner’s Use 1 2 3 4 5 Total

2 9701/21/M/J/12 © UCLES 2012 For Examiner’s Use Answer all the questions in the spaces provided. 1 Oxides are compounds which usually contain oxygen combined with one other element. Oxides are classifi ed as follows. acidic alkaline amphoteric basic (a) Using these terms only, complete the table to describe the oxides of the elements of the third period of the Periodic Table sodium to sulfur. Na2O MgO Al 2O3 SiO2 P4O10 SO2 Cl 2O7 acidic [4] (b) Give the names of two elements from sodium to chlorine which form more than one oxide. … and … [1] (c) Sodium reacts with water. (i) Describe, as fully as you can, what you would see when a piece of sodium is reacted with water. … … … (ii) Write an equation for the reaction of sodium with water. … [4]

3 9701/21/M/J/12 © UCLES 2012 [Turn over For Examiner’s Use (d) Sulfur dioxide is present in small, but signifi cant, amounts in the Earth’s atmosphere. (i) State one way by which sulfur dioxide enters the atmosphere. … (ii) Give the formula of another sulfur compound which is formed in the atmosphere from sulfur dioxide. … (iii) What are the environmental consequences of the compound you have identifi ed in (ii)? … [3] (e) Sulfur dioxide is used as a food preservative. What property of sulfur dioxide enables it to act in this way? … [1] (f) Another sulfur compound which is present in the Earth’s atmosphere is carbonyl sulfi de, OCS. The sequence of atoms in the molecule is oxygen-carbon-sulfur and the molecule is not cyclic. (i) Draw a ‘dot-and-cross’ diagram of the OCS molecule. Show outer electrons only. (ii) Suggest a value for the O – C – S bond angle. … [2] [Total: 15]

4 9701/21/M/J/12 © UCLES 2012 For Examiner’s Use 2 Ammonium sulfate, (NH4)2SO4, is widely used as a fertiliser. In order to determine its percentage purity, a sample of ammonium sulfate fertiliser was analysed by reacting a known amount with an excess of NaOH(aq) and then titrating the unreacted NaOH with dilute HCl. (a) Ammonium sulfate reacts with NaOH in a 1 : 2 ratio. Complete and balance the equation for this reaction. (NH4)2SO4 + 2NaOH → …NH3 + … + … [2] (b) A 5.00 g sample of a fertiliser containing (NH4)2SO4 was warmed with 50.0 cm3 (an excess) of 2.00 mol dm–3 NaOH. When all of the ammonia had been driven off, the solution was cooled. The remaining NaOH was then titrated with 1.00 mol dm–3 HCl and 31.2 cm3 were required for neutralisation. (i) Write a balanced equation for the reaction between NaOH and HCl. … (ii) Calculate the amount, in moles, of HCl in 31.2 cm3 of 1.00 mol dm–3 HCl. (iii) Calculate the amount, in moles, of NaOH in 50.0 cm3 of 2.00 mol dm–3 NaOH. (iv) Use your answers to (i), (ii) and (iii) to calculate the amount, in moles, of NaOH used up in the reaction with (NH4)2SO4.

5 9701/21/M/J/12 © UCLES 2012 [Turn over For Examiner’s Use (v) Use your answer to (iv) and the equation in (a) to calculate the amount, in moles, of (NH4)2SO4 that reacted with NaOH. (vi) Use your answer to (v) to calculate the mass of (NH4)2SO4 that reacted with NaOH. (vii) Hence, calculate the percentage purity of the ammonium sulfate fertiliser. [7] [Total: 9]

6 9701/21/M/J/12 © UCLES 2012 For Examiner’s Use 3 Methanol, CH3OH, is considered to be a possible alternative to fossil fuels, particularly for use in vehicles. Methanol can be produced from fossil fuels and from agricultural waste. It can also be synthesised from carbon dioxide and hydrogen. (a) Defi ne, with the aid of an equation which includes state symbols, the standard enthalpy change of formation of carbon dioxide. equation … defi nition … … … [3] (b) Relevant values for the reaction that synthesises methanol are given in the table. compound CO2(g) –394 CH3OH(g) –201 H2O(g) –242 (i) Use these values to calculate for this synthesis of methanol. Include a sign in your answer. CO2(g) + 3H2(g) CH3OH(g) + H2O(g) = …kJ mol–1 (ii) Suggest one possible environmental advantage of this reaction. Explain your answer. … … [5]

7 9701/21/M/J/12 © UCLES 2012 [Turn over For Examiner’s Use (c) The synthesis of methanol is carried out at about 500 K with a pressure of between 40 and 100 atmospheres (between 4 × 106 Pa and 10 × 107 Pa) and using a catalyst. The use of such conditions will affect both the rate of reaction and the equilibrium yield. In the spaces below, explain the effects of higher temperature, higher pressure, and the use of a catalyst on the equilibrium yield of methanol. higher temperature effect … explanation … … higher pressure effect … explanation … … use of catalyst effect … explanation … … [6] [Total: 14]

8 9701/21/M/J/12 © UCLES 2012 For Examiner’s Use 4 One method of preparing ethene in a school or college laboratory is from ethanol by using the apparatus shown below. mineral wool and ethanol pumice water ethene strong heat (a) (i) Write a balanced equation for this reaction. … (ii) What type of reaction is this? … (iii) Give the chemical name of a reagent other than pumice that could be used to carry out this reaction. It is not necessary to use the same apparatus. … [3] (b) Ethene is bubbled into two separate test-tubes, one containing aqueous hydrogen bromide and the other containing cold, dilute acidifi ed potassium manganate(VII). In each case, describe any colour changes you would see and give the structural formula of the organic product. aqueous hydrogen bromide cold, dilute acidifi ed potassium manganate(VII) colour at start colour after reaction structural formula of organic product [4]

9 9701/21/M/J/12 © UCLES 2012 [Turn over For Examiner’s Use (c) Cyclohexene has the following structural formula. (i) What is the molecular formula of cyclohexene? … (ii) Draw the structural formula of the compound formed when cyclohexene is reacted with bromine. (iii) State as fully as you can what type of reaction this is. … (iv) Draw the structural formula of the compound formed when cyclohexene is reacted with hot concentrated acidifi ed potassium manganate(VII). [5] [Total: 12]

10 9701/21/M/J/12 © UCLES 2012 For Examiner’s Use 5 Organic compounds which contain oxygen may contain alcohol, aldehyde, carboxylic acid, ester or ketone functional groups. The functional groups may be identifi ed by their reactions with specifi c reagents. Compound X has the empirical formula CH2O and Mr of 90. (a) There is no reaction when X is treated with NaHCO3. What functional group does this test show to be not present in X? … [1] (b) When 0.600 g of X is reacted with an excess of Na, 160 cm3 of H2, measured at room temperature and pressure, is produced. (i) What functional group does this reaction show to be present in X? … (ii) Use the data to calculate the amount, in moles, of hydrogen atoms produced from 0.600 g of X. (iii) Hence, show that each molecule of X contains two of the functional groups you have given in (i). [4]

11 9701/21/M/J/12 © UCLES 2012 [Turn over For Examiner’s Use (c) When X is warmed with Fehling’s reagent, a brick red precipitate is formed. Treatment of X with 2,4-dinitrophenylhydrazine reagent produces an orange solid. (i) What functional group do these reactions show to be present in X? Draw the displayed formula of this functional group. (ii) Use your answers to (b)(i), (b)(ii) and (c)(i) to deduce the structural formula of X. (iii) What is the structural formula of the organic product of the reaction of X with Fehling’s reagent? [3] (d) Compound X can be both oxidised and reduced. (i) Give the structural formula of the compound formed when X is reacted with NaBH4 under suitable conditions. (ii) Give the structural formula of the compound formed when X is heated under refl ux with acidifi ed K2Cr2O7. [2] [Total: 10]

12 Permission to reproduce items where third-party owned material protected by copyright is included has been sought and cleared where possible. Every reasonable effort has been made by the publisher (UCLES) to trace copyright holders, but if any items requiring clearance have unwittingly been included the publisher will be pleased to make amends at the earliest possible opportunity. University of Cambridge International Examinations is part of the Cambridge Assessment Group. Cambridge Assessment is the brand name of University of Cambridge Local Examinations Syndicate (UCLES), which is itself a department of the University of Cambridge. 9701/21/M/J/12 © UCLES 2012 BLANK PAGE

UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS GCE Advanced Subsidiary Level and GCE Advanced Level MARK SCHEME for the May/June 2012 question paper for the guidance of teachers 9701 CHEMISTRY 9701/21 Paper 2 (AS Structured Questions), maximum raw mark 60 This mark scheme is published as an aid to teachers and candidates, to indicate the requirements of the examination. It shows the basis on which Examiners were instructed to award marks. It does not indicate the details of the discussions that took place at an Examiners’ meeting before marking began, which would have considered the acceptability of alternative answers. Mark schemes must be read in conjunction with the question papers and the report on the examination. • Cambridge will not enter into discussions or correspondence in connection with these mark schemes. Cambridge is publishing the mark schemes for the May/June 2012 question papers for most IGCSE, GCE Advanced Level and Advanced Subsidiary Level syllabuses and some Ordinary Level syllabuses.

Page 2 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2012 9701 21 © University of Cambridge International Examinations 2012 1 (a) Na2O MgO Al2O3 SiO2 P4O10 SO2 Cl2O7 alkaline basic amphoteric acidic acidic acidic acidic Na2O is alkaline – allow basic (1) MgO is basic – allow alkaline (1) Al2O3 is amphoteric (1) SiO2, P4O10, and SO2 are all acidic (1) [4] (b) any two from: sodium, phosphorus, sulfur and chlorine two names required (1) [1] (c) (i) any three from: floats vigorous/violent reaction occurs melts/forms a sphere moves disappears – allow dissolves effervescence/gas produced (any 3) (ii) Na + H2O → NaOH + ½H2 or 2Na + 2H2O → 2NaOH + H2 (1) [4] (d) (i) combustion of fossil fuels – e.g. from car engines from car exhausts or during the extraction of metals from sulfide ores or volcanic eruptions/burning sulfur from volcanoes or burning biomass (1) (ii) H2SO4 or SO3 allow H2SO3 formula required (1) (iii) acid rain or its consequences e.g. damage to buildings, damage to crops, plants, marine life deforestation or SO3 is toxic (1) [3] (e) it is a reducing agent/antioxidant or it kills bacteria (1) [1]

Page 3 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2012 9701 21 © University of Cambridge International Examinations 2012 (f) (i) (1) (ii) 180° (1) [2] [Total: 15] 2 (a) (NH4)2SO4 + 2NaOH → 2NH3 + Na2SO4 + 2H2O correct products (1) correctly balanced equation (1) [2] (b) (i) NaOH + HCl → NaCl + H2O (1) (ii) n(HCl) = 1000 31.2 × 1.00 = 0.0312 = 0.03 (1) (iii) n(NaOH) = 1000 50.0 × 2.00 = 0.10 (1) (iv) n(NaOH) used up = 0.10 – 0.0312 = 0.0688 = 0.07 (1) (v) n[(NH4)2SO4] = 2 0.0688 = 0.0344 = 0.03 (1) (vi) mass of (NH4)2SO4 = 0.0344 × 132 = 4.5408 = 4.54 (1) (vii) percentage purity = 5.00 100 4.5408× = 90.816 = 90.8 (1) [7] [Total: 9]

Page 4 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2012 9701 21 © University of Cambridge International Examinations 2012 3 (a) C(s) + O2(g) → CO2(g) (1) the enthalpy change/energy change/heat change when one mole of a compound/CO2 (1) is formed from its elements in their standard states (1) [3] (b) (i) CO2(g) + 3H2(g) CH3OH(g) + H2O(g) ∆Ho f/kJ mol–1 –394 0 –201 –242 ∆Ho reaction = –201 + (–242) – (–394) (1) –49 kJ mol–1 (1) correct sign (1) (ii) removal of CO2 from the atmosphere (1) CO2 is a greenhouse gas/causes global warming (1) [5] (c) In this part, in each case, the ‘effect’ must be correctly stated in order to gain the explanation mark. higher temperature yield is reduced/equilibrium goes to LHS (1) because forward reaction is exothermic/reverse reaction is endothermic (1) higher pressure yield is increased or equilibrium goes to RHS (1) fewer moles/molecules on RHS or more moles/molecules on LHS (1) use of catalyst yield does not change (1) forward and backward rates speeded up by same amount (1) [6] [Total: 14]

Page 5 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2012 9701 21 © University of Cambridge International Examinations 2012 4 (a) (i) C2H5OH → C2H4 + H2O (1) (ii) elimination or dehydration (1) (iii) phosphoric acid or concentrated sulfuric acid sulfuric acid must be ‘concentrated’ allow aluminium oxide (1) [3] (b) with HBr with MnO4 – colour at start colourless purple or pink colour after reaction colourless colourless or decolourised structural formula of product CH3CH2Br HOCH2CH2OH with hydrogen bromide from colourless to colourless both colours required do not allow ‘clear’ instead of colourless (1) CH3CH2Br (1) with potassium manganate(VII) from purple/pink to colourless/decolourised both colours required (1) HOCH2CH2OH (1) [4] (c) (i) C6H10 (1) (ii) accept answers which have –CH2– in the ring (1) (iii) electrophilic (1) addition (1) (iv) CO2H CO2H or HO2C(CH2)4CO2H or HO2CCH2CH2CH2CH2CO2H (1) accept answers which have –CH2– in the ring [5] [Total: 12]

Page 6 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2012 9701 21 © University of Cambridge International Examinations 2012 5 (a) carboxylic acid or –CO2H or –COOH (1) [1] (b) (i) alcohol (1) (ii) n(H2) = 24000 160 = 6.67 × 10–3 mol (1) n(H atoms) = 2 × 6.67 × 10–3 mol = 1.33 × 10–2 mol (1) (iii) n(X) = 90 0.600 = 6.67 × 10–3 mol n(X) : n(H atoms) = 6.67 × 10–3 : 1.33 × 10–2 = 1 : 2 since each –OH group produces one H atom there are two –OH groups (1) [4] (c) (i) or (1) (ii) HOCH2CH(OH)CHO as the minimum allow the gem diols (HO)2CHCH2CHO or CH3C(OH)2CHO (1) (iii) HOCH2CH(OH)CO2H or HOCH2CH(OH)CO2 – (1) [3] (d) (i) HOCH2CH(OH)CH2OH (1) (ii) HO2CCOCO2H (1) [2] [Total: 10]