Cambridge A Level Chemistry 9701 — 2016 Oct/Nov Paper 5 · Variant 3

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 an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. DO NOT WRITE IN ANY BARCODES. Answer all questions. Electronic calculators may be used. You may lose marks if you do not show your working or if you do not use appropriate units. Use of a Data Booklet is unnecessary. 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 9701/53 Paper 5 Planning, Analysis and Evaluation October/November 2016 1 hour 15 minutes Candidates answer on the Question Paper. No Additional Materials are required. This document consists of 11 printed pages and 1 blank page. [Turn over IB16 11_9701_53/FP © UCLES 2016 *9448950970* Cambridge International Examinations Cambridge International Advanced Subsidiary and Advanced Level

2 9701/53/O/N/16 © UCLES 2016 1 When hydrated barium chloride, BaCl 2.xH2O, dissolves in water, Ba2+(aq) and Cl –(aq) ions are formed. The concentration of chloride ions in solution can be determined by titration with aqueous silver nitrate of known concentration. Ag+(aq) + Cl –(aq) → AgCl (s) The indicator for the reaction is aqueous potassium chromate(VI), K2CrO4(aq). At the endpoint of the titration, it forms a red precipitate in the presence of excess silver ions. (a) The solubilities, in g dm–3, of different ionic compounds at 20 °C are given in the table below. anion cation Cl – CrO4 2– SO4 2– Ag+ 0.0019 0.022 293 Ba2+ 358 0.0028 0.00245 With reference to these data, where relevant, answer the following questions. (i) Name the red precipitate and give an equation for its formation. name: … equation: … [2] Sulfuric acid must be added to the solution to prevent the Ba2+(aq) ions from interfering with the action of the potassium chromate(VI) indicator. (ii) How would Ba2+(aq) ions interfere with the action of this indicator? … … [1] (iii) How does the addition of sulfuric acid prevent Ba2+(aq) ions from interfering with the action of this indicator? … … [1]

3 9701/53/O/N/16 © UCLES 2016 [Turn over (b) In an initial rough titration, excess silver nitrate solution is added so that the endpoint is exceeded. Draw a sketch graph to show how the mass of silver chloride varies with the volume of silver nitrate added. Label both axes. 0 [2]

4 9701/53/O/N/16 © UCLES 2016 (c) You are to plan a titration experiment to determine the value of x in BaCl 2.xH2O. You are provided with the following materials. 3.00 g of hydrated barium chloride, BaCl 2.xH2O 0.050 mol dm–3 aqueous silver nitrate 1.0 mol dm–3 potassium chromate(VI) solution 1.0 mol dm–3 sulfuric acid (i) Name three pieces of volumetric apparatus you would use, with their capacities in cm3. 1 … 2 … 3 … [2] (ii) Describe how you would make a solution of barium chloride that is suitable for use in your titration. … … … … … … [2] (iii) A known volume of barium chloride solution is transferred to a conical flask. In what order should the other three solutions then be added to the flask? first … second … third … [1] (iv) How would you ensure that your titration result is reliable? … … [1]

5 9701/53/O/N/16 © UCLES 2016 [Turn over (v) In another experiment, a student dissolved 3.13 g of hydrated barium chloride, BaCl 2.xH2O, in distilled water to give 1.00 dm3 of solution. It was calculated that the concentration of Ba2+(aq) ions was 0.0128 mol dm–3. Determine the value of x in BaCl 2.xH2O. [Ar: Ba, 137.3; Cl, 35.5; H, 1.0; O, 16.0] x = … [2] (d) The following information gives some of the hazards associated with the chemicals used in the procedure. Barium chloride Solid barium chloride is classified as toxic. Solutions equal to or more concentrated than 0.4 mol dm–3 are classified as moderate hazard and are harmful if swallowed. Solutions less concentrated than 0.4 mol dm–3 are classified as non-hazardous. Potassium chromate(VI) All solutions more concentrated than 0.9 mol dm–3 are classified as health hazard. They may cause skin, eye and respiratory irritation. Silver nitrate Solutions equal to or more concentrated than 0.18 mol dm–3 are classified as corrosive. Solutions equal to or more concentrated than 0.06 mol dm–3 but less than 0.18 mol dm–3 are classified as moderate hazard and cause skin and eye irritation. Solutions less concentrated than 0.06 mol dm–3 are classified as non-hazardous. Identify one hazard that must be considered when planning the experiment and describe a precaution, other than eye protection, that should be taken to keep risks from this hazard to a minimum. hazard: … precaution: … … [1] [Total: 15]

6 9701/53/O/N/16 © UCLES 2016 BLANK PAGE

7 9701/53/O/N/16 © UCLES 2016 [Turn over 2 Sucrose, C12H22O11, is a naturally occurring sugar found in sugarcane and many fruits. It can be hydrolysed in acidic solution to give glucose and fructose. All three molecules are chiral and will rotate the plane of polarised light. The degree of rotation is known as the optical rotation, α. CH2OH HO OH OH OH + + H2O O glucose CH2OH CH2OH HO OH OH O O sucrose CH2OH OH HO OH O CH2OH CH2OH HO OH O fructose H+ catalyst In the presence of excess water, the reaction can be considered to be first order with respect to sucrose concentration. The progress of the reaction can be monitored using a polarimeter, which measures the optical rotation, α, of the solution. The more concentrated the solution, the greater the optical rotation of the solution. The concentration of sucrose at time t can be represented as (α – αfinal), where αfinal is the optical rotation of the solution after 6 hours. The mathematical relationship is given by the following equation. log10(α – αfinal) = A – 2.30 kt A is a constant. k is the rate constant.

8 9701/53/O/N/16 © UCLES 2016 (a) The experimentally determined values of optical rotation during the hydrolysis of sucrose at 298 K are recorded below. Process the results to allow you to plot a graph of log10(α – αfinal) against time, t. Calculate (α – αfinal) and record it to 1 decimal place. Calculate log10(α – αfinal) and record it to 2 decimal places. time / s optical rotation, α (α – αfinal) log10(α – αfinal) 0 39.9 300 29.1 600 21.3 900 15.5 1200 10.6 1500 6.2 1800 2.4 2100 –0.3 2400 –2.5 2700 –4.5 αfinal –12.0 [2] (b) (i) Plot a graph on the grid on page 9 to show how log10(α – αfinal) varies with time, t. Use a cross (×) to plot each data point. Draw the line of best fit. [2] (ii) State and explain whether the results and your graph confirm the relationship log10(α – αfinal) = A – 2.30 kt . … … … [1]

9 9701/53/O/N/16 © UCLES 2016 [Turn over log10( – ) α α final time / s 2000 3000 1000 1500 2500 500 0 1.8 1.7 1.6 1.5 1.4 1.3 1.2 1.1 1.0 0.9 0.8 0.7 0.6

10 9701/53/O/N/16 © UCLES 2016 (c) (i) Determine the gradient of the graph. State the co-ordinates of both points you used for your calculation. Record the value of the gradient to three significant figures. co-ordinates 1 … co-ordinates 2 … gradient = … s–1 [2] (ii) Use the gradient value to calculate a value for k in the expression shown. log10(α – αfinal) = A – 2.30 kt [2]

11 9701/53/O/N/16 © UCLES 2016 [Turn over (d) The graph below shows the results obtained from a second hydrolysis of sucrose reaction performed at a different temperature. – α αfinal time / s 45.0 40.0 35.0 30.0 25.0 20.0 15.0 10.0 5.0 0.0 0 400 800 1200 1600 2000 2400 2800 (i) The point at time = 2000 s is considered to be anomalous. Suggest what caused the anomaly. … … … [1]

12 9701/53/O/N/16 © UCLES 2016 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. To avoid the issue of disclosure of answer-related information to candidates, all copyright acknowledgements are reproduced online in the Cambridge International Examinations Copyright Acknowledgements Booklet. This is produced for each series of examinations and is freely available to download at www.cie.org.uk after the live examination series. 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. (ii) Use the graph to determine the half-life, t½, of this reaction. State the co-ordinates of both points you used in your calculation. co-ordinates 1 … co-ordinates 2 … half-life = … s [2] (iii) For a first-order reaction, the following relationship exists. half-life, t½ = 0.693 k' Use this relationship and your answer to (ii) to determine k', the rate constant for this second hydrolysis reaction. If you have been unable to determine the half-life of the reaction in (ii), you may use the value t½ = 500 s, though this is not the correct answer. k' = … s–1 [1] (iv) State whether the temperature of the second reaction was higher or lower than that of the first. Explain your answer with reference to the answers you obtained in (c)(ii) and (d)(iii). If you have been unable to calculate a value for k in (c)(ii), you may use the value k = 8.00 × 10–4, though this is not the correct answer. … … … [1] (v) Would the value of the half-life change if the reaction were repeated with twice the initial concentration of sucrose? Give a reason for your answer. … … … [1] [Total: 15]

® IGCSE is the registered trademark of Cambridge International Examinations. This document consists of 7 printed pages. © UCLES 2016 [Turn over Cambridge International Examinations Cambridge International Advanced Subsidiary and Advanced Level CHEMISTRY 9701/53 Paper 5 Planning, Analysis and Evaluation October/November 2016 MARK SCHEME Maximum Mark: 30 Published 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 should be read in conjunction with the question paper and the Principal Examiner Report for Teachers. Cambridge will not enter into discussions about these mark schemes. Cambridge is publishing the mark schemes for the October/November 2016 series for most Cambridge IGCSE®, Cambridge International A and AS Level components and some Cambridge O Level components.

Questio 1(a)(i 1(a)(ii 1(a)(ii 1(b) 1(c)(i Page 2 on ) silver chro 2Ag+ + CrO OR 2Ag+ + OR 2AgN i) insoluble / i) insoluble / correctly l straight lin ) Volumetri pipette (g burette Cambridge Inte omate(VI) / silver O4 2– → Ag2CrO4 + K2CrO4 → Ag2C O3 + K2CrO4 → A / solid barium ch / solid barium su abelled axes ne through origin c/graduated flas raduated) Mark ernational AS/A r chromate CrO4 + 2K+ Ag2CrO4 + 2KNO hromate(VI) / bar ulfate is formed n AND reaches sk 250 cm3 25 cm3 50 cm3 k Scheme A Level – Octob © UCLES 2016 Answer O3 rium chromate w a plateau ber/November 2 would form Syllabus 2016 9701 s Paper 53 Mark 1 1 2 1 1 1 1 1 1 2 2

Page 3 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2016 9701 53 © UCLES 2016 Question Answer Mark 1(c)(ii) Dissolve / stir / mix known mass / all of hydrated salt in (a container with) (distilled water) (Transfer / add to a) volumetric flask, make to mark (with distilled water) or to the volume of the stated volumetric flask (in 1(c)(i) or 1(c)(ii)) NOTE: Water must be mentioned at least once for one mark to be awarded. Distilled/deionised/purified water must be mentioned for 2 marks to be awarded. 1 1 2 1(c)(iii) first = sulfuric acid second = potassium chromate(VI) third = silver nitrate 1 1 1(c)(iv) experiment / titration is repeated to get concordant titre 1 1 1(c)(v) 0.0128 × 208.3 = 2.67 g of BaCl2 AND 3.13 – 2.67 = 0.46 g of H2O x = (0.46 / 18.0) ÷ 0.0128 = 2 1 1 2

Page 4 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2016 9701 53 © UCLES 2016 Question Answer Mark 1(d) Potassium chromate (solution) – (health hazard in context of) respiratory irritation AND fume cupboard / face / nose / mouth mask … OR Potassium chromate – (health hazard in context of) skin irritation AND (chemical resistant) gloves ……………………………………………………………… OR barium chloride (solid) as toxic AND (chemical resistant) gloves / large dilution on disposal ……………………………………………………………… OR Sulfuric acid as irritant / skin irritant AND (chemical resistant) gloves 1 1 Total: 15

Page 5 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2016 9701 53 © UCLES 2016 Question Answer Mark 2(a) Column C data correct Column D data correct and given to 2 dp C D (ߙ– ߙஶ) log10(ߙ– ߙஶ) time 51.9 1.72 0 41.1 1.61 300 33.3 1.52 600 27.5 1.44 900 22.6 1.35 1200 18.2 1.26 1500 14.4 1.16 1800 11.7 1.07 2100 9.5 0.98 2400 7.5 0.88 2700 1 1 2

Page 6 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2016 9701 53 © UCLES 2016 Question Answer Mark 2(b)(i) All ten points plotted correctly Best-fit straight line drawn 1 1 2 2(b)(ii) (Yes) most of the points are on the line OR only a few points are not on the line 1 1 2(c)(i) Co-ordinates read and recorded correctly Correctly calculated value of the gradient given to 3sf and using the candidate’s co-ordinates correctly 1 1 2 2(c)(ii) k = candidate’s gradient × (– 2.30) Correct answer 1 1 2 2(d)(i) Reading / value of α was read / taken / recorded too early 1 1 2(d)(ii) Two co-ordinates on line correctly read and stated AND One y value must be half the other t½ correctly determined from candidate's co-ordinates values provided y1 = y2 / 2 1 1 2 2(d)(iii) Correctly calculated value for k’ = 1 2 0.693 t 1 1

Page 7 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2016 9701 53 © UCLES 2016 Question Answer Mark 2(d)(iv) Second reaction took place at higher temperature AND because k’ (second k value) is larger 1 1 2(d)(v) No OR the half-life would not change AND half-life is independent of cencentration OR the reaction is first order (with respect to sucrose) 1 1 Total: 15