Cambridge A Level Physical Science 8780 — 2012 Oct/Nov Paper 4 · Variant 1

This document consists of 11 printed pages and 5 blank pages. DC (NH/JG) 50319/4 © UCLES 2012 [Turn over UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS General Certificate of Education Advanced Subsidiary Level * 8 9 1 9 4 7 5 8 1 1 * PHYSICAL SCIENCE 8780/04 Paper 4 Advanced Practical Skills October/November 2012 1 hour 30 minutes Candidates answer on the Question Paper. Additional Materials: As listed in the Confidential Instructions READ THESE INSTRUCTIONS FIRST Write your Centre number, candidate number and name on all the work you hand in. Give details of the practical session and laboratory where appropriate, in the boxes provided. Write in dark blue or black pen. You may use a pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. DO NOT WRITE IN ANY BARCODES. Answer both questions. You will be allowed to work with the apparatus for a maximum of 45 minutes for each question. You are advised to show all working in calculations. Use of a Data Booklet is unnecessary. Qualitative Analysis Notes are printed on pages 12 and 13. 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. For Examiner’s Use 1 2 Total Session Laboratory

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3 8780/04/O/N/12 © UCLES 2012 [Turn over For Examiner’s Use 1 You are going to investigate the potential difference across a resistor using the circuit shown in Fig. 1.1. (a) Set up the circuit as shown in Fig. 1.1. The switch S may be an integral part of the power supply. mA Ÿ P S moveable contact C power supply metre rule crocodile clip crocodile clip resistance wire l + – Fig. 1.1 Ask your Supervisor if you need help to set up the circuit. You may lose one mark. (b) (i) Press the moveable contact C on the resistance wire and adjust the position so that l is approximately 0.25 m. Close switch S and record your value of l and the current I through the ammeter. Open switch S as soon as you have taken your reading. l = … m I = … mA (ii) Calculate the potential difference V across the 68 Ω resistor using the equation V = IR, where R = 68 Ω. V = … V

4 8780/04/O/N/12 © UCLES 2012 For Examiner’s Use (c) You are going to measure I at five further values of l between 0.10 m and 0.90 m. You will need to choose appropriate values. (i) Construct a table in which to record all six sets of measurements of l and I. Include an extra column for V. (ii) Record in the table your values of l and I and V from part (b). (iii) Adjust the position of the contact C. Close switch S. Measure and record the new values of l and I. Repeat until all six sets of readings are completed. Open switch S. (iv) For each value of l, calculate the potential difference V across the 68 Ω resistor. Use the equation V = IR, where R = 68 Ω. Record these values in your table. (d) (i) On the grid provided, plot your values of V on the y-axis against l on the x-axis. Draw the straight line of best fit. (ii) Calculate the gradient of the graph. Show your working. gradient = … (iii) Determine the y-intercept. y-intercept = …

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6 8780/04/O/N/12 © UCLES 2012 For Examiner’s Use (e) It is suggested that the relationship between V and l is V = 0.76rl + 0.76R where r is the resistance per metre of the resistance wire and R is the resistance of the resistor P. Use the results from (d)(ii) and (iii) to calculate the value of (i) r, r = … Ω m–1 (ii) R. R = … Ω (f) Identify one significant source of experimental uncertainty or limitation of the procedure in this experiment. … … … [Total: 15]

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8 8780/04/O/N/12 © UCLES 2012 For Examiner’s Use 2 (a) You are to carry out a titration to determine the concentration of hydrochloric acid in solution X. You are provided with the following: solution X, dilute hydrochloric acid of unknown concentration, solution Y, 0.100 mol dm–3 sodium hydroxide, phenolphthalein indicator. Titration (i) Fill the burette with solution Y, 0.100 mol dm–3 sodium hydroxide. Use the pipette to transfer 25.0 cm3 of solution X, dilute hydrochloric acid, into the conical flask and add 2 to 3 drops of phenolphthalein indicator. Titrate the acid in the flask with solution Y until the first permanent pale pink colour. Perform a rough (trial) titration and sufficient further titrations to obtain accurate results. Record your titration results in a suitable table in the space below. Make certain that your recorded results show the precision of your working. (ii) From your titration results obtain a volume of solution Y to be used in your calculations. Show clearly how you obtained this volume. volume of Y = … cm3

9 8780/04/O/N/12 © UCLES 2012 [Turn over For Examiner’s Use Calculation Show your working and appropriate significant figures in all of your calculations. NaOH + HCl NaCl + H2O (iii) Calculate the concentration of hydrochloric acid in solution X. concentration of hydrochloric acid in X = … mol dm–3 (iv) This experiment could have been carried out using 10.0 cm3 of dilute hydrochloric acid rather than 25.0 cm3. Explain why using 25.0 cm3 is likely to give a more accurate value for the hydrochloric acid concentration. … … … … …

10 8780/04/O/N/12 © UCLES 2012 For Examiner’s Use (b) P is an aqueous solution of a metal nitrate. The cation is unknown. Carry out the specified tests to enable you to identify the unknown cation. At each stage of any test you are to record details of the following: • colour changes seen • the formation of any precipitate • the solubility of such precipitates in an excess of the reagent added. You should indicate clearly at what stage in a test a change occurs. Record all of your observations in the table below. test observations (i) To 0.5 cm depth of solution in a test-tube, add a few drops of 2.0 mol dm–3 aqueous sodium hydroxide. Continue adding aqueous sodium hydroxide until there is no further change. (ii) To 0.5 cm depth of solution in a test-tube, add a few drops of aqueous ammonia. Continue adding aqueous ammonia until there is no further change.

11 8780/04/O/N/12 © UCLES 2012 [Turn over For Examiner’s Use (iii) Conclusions Use the Qualitative Analysis Notes on page 12 to identify the unknown cation, giving supporting evidence from your observations. The unknown cation is … . evidence … … … … [Total: 15]

12 8780/04/O/N/12 © UCLES 2012 Qualitative Analysis Notes Key: [ppt. = precipitate] 1 Reactions of aqueous cations ion reaction with NaOH(aq) NH3(aq) aluminium, Al3+(aq) white ppt. soluble in excess white ppt. insoluble in excess ammonium, NH4 +(aq) no ppt. ammonia produced on heating barium, Ba2+(aq) no ppt. (if reagents are pure) no ppt. calcium, Ca2+(aq) white ppt. with high [Ca2+(aq)] no ppt. chromium(III), Cr3+(aq) grey-green ppt. soluble in excess giving dark green solution grey-green ppt. insoluble in excess copper(II), Cu2+(aq) pale blue ppt. insoluble in excess blue ppt. soluble in excess giving dark blue solution iron(II), Fe2+(aq) green ppt. turning brown on contact with air insoluble in excess green ppt. turning brown on contact with air insoluble in excess iron(III), Fe3+(aq) red-brown ppt. insoluble in excess red-brown ppt. insoluble in excess lead(II), Pb2+(aq) white ppt. soluble in excess white ppt. insoluble in excess magnesium, Mg2+(aq) white ppt. insoluble in excess white ppt. insoluble in excess manganese(II), Mn2+(aq) off-white ppt. rapidly turning brown on contact with air insoluble in excess off-white ppt. rapidly turning brown on contact with air insoluble in excess zinc, Zn2+(aq) white ppt. soluble in excess white ppt. soluble in excess [Lead(II) ions can be distinguished from aluminium ions by the insolubility of lead(II) chloride.]

13 8780/04/O/N/12 © UCLES 2012 2 Reactions of anions ion reaction carbonate, CO3 2– CO2 liberated by dilute acids chromate(VI), CrO4 2– (aq) yellow solution turns orange with H+(aq); gives yellow ppt. with Ba2+(aq); gives bright yellow ppt. with Pb2+(aq) chloride, Cl– (aq) gives white ppt. with Ag+(aq) (soluble in NH3(aq)); gives white ppt. with Pb2+(aq) bromide, Br– (aq) gives pale cream ppt. with Ag+(aq) (partially soluble in NH3(aq)); gives white ppt. with Pb2+(aq) iodide, I– (aq) gives yellow ppt. with Ag+(aq) (insoluble In NH3(aq)); gives yellow ppt. with Pb2+(aq) nitrate, NO3 – (aq) NH3 liberated on heating with OH–(aq) and Al foil nitrite, NO2 – (aq) NH3 liberated on heating with OH–(aq) and Al foil, NO liberated by dilute acids (colourless NO → (pale) brown NO2 in air) sulfate, SO4 2– (aq) gives white ppt. with Ba2+(aq) or with Pb2+ (insoluble in excess dilute strong acid) sulfite, SO3 2– (aq) SO2 liberated with dilute acids; gives white ppt. with Ba2+(aq) (soluble in excess dilute strong acid) 3 Tests for gases gas test and test result ammonia, NH3 turns damp red litmus paper blue carbon dioxide, CO2 gives a white ppt. with limewater (ppt. dissolves with excess CO2) chlorine, Cl2 bleaches damp litmus paper hydrogen, H2 “pops” with a lighted splint oxygen, O2 relights a glowing splint sulfur dioxide, SO2 turns acidified aqueous potassium dichromate(VI) from orange to green

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16 8780/04/O/N/12 © UCLES 2012 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. BLANK PAGE

CAMBRIDGE INTERNATIONAL EXAMINATIONS GCE Advanced Subsidiary Level MARK SCHEME for the October/November 2012 series 8780 PHYSICAL SCIENCE 8780/04 Paper 4 (Advanced Practical Skills), maximum raw mark 30 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 2012 series for most IGCSE, GCE Advanced Level and Advanced Subsidiary Level components and some Ordinary Level components.

Page 2 Mark Scheme Syllabus Paper GCE AS LEVEL – October/November 2012 8780 04 © Cambridge International Examinations 2012 1 (a) Apparatus connected up correctly, check sensible figure for I given in mA [1] (b) 6 sets of sensible readings [1] Range: at least from 0.15 – 0.85 m, no gaps greater than 0.2 m [1] Quality V increases consistently as l increases (check from graph) [1] (c) All columns headed: l/m, I/A, V/V (accept “l in m”, but NOT “l m” etc) [1] All raw data in a column to the same precision [1] The calculated column correct and V to same number (or 1 more) significant figures as I [1] (d) (i) Axes labelled, sensible scales chosen (at least half graph paper used and no awkward scales: false origin will almost certainly need to be used) [1] Points plotted correctly (minimum 5 to within ½ square) [1] Best-fit line ignoring any anomalous points [1] (ii) Attempt to measure gradient using at least half drawn scale and correct substitution of figures into calculation [1] (Do not allow use of figures from table) (iii) Intercept correctly read from graph or calculated [1] (e) (i) Use of gradient to find r [1] (ii) Use of intercept to find R [1] (iii) Parallax when reading l, thickness of crocodile clip C, wire bends, or other [1] [TOTAL: 15]

Page 3 Mark Scheme Syllabus Paper GCE AS LEVEL – October/November 2012 8780 04 © Cambridge International Examinations 2012 Question 2 Supervisor’s Report Check all subtractions in (a). Use the titres, corrected where necessary, to select the “best average” titre to be used as an accuracy standard using the following hierarchy: • value of 2 identical titres • average of titres within 0.05 cm3 • average of titres within 0.10 cm3, etc. Candidate scripts Check and correct all subtractions as above for accuracy and concordancy marks. 2 (a) (i) Tabulates initial and final burette readings(not volume) and volume added in table [1] Table has correct labels and units (cm3) Tabulation may be vertical or horizontal Do NOT award this mark if 50 is used as the initial burette reading Burette readings for all accurate readings and titres in the titration table recorded to the nearest 0.05 cm3 [1] Has at least two uncorrected titres within 0.1 cm3 [1] Titre labelled ‘rough’ may be included Accuracy – ranges [2] Give 2 marks if two titres within 0.30 cm3 of supervisor average Give only 1 mark if one titre within 0.30 cm3 of supervisor average (ii) Working must be shown in this section or the selected titres ticked in the titration table Candidate selects/calculates appropriate “average” from any titre values within 0.20 cm3 [1] Candidate is permitted to use a titre labelled “rough” or “trial” Where all titres are given to 1 decimal place the average should be calculated correct to 1 or 2 decimal places Where any titre is recorded to 2 decimal places, the average should be calculated to 2 decimal places or rounded to the nearest 0.05 cm3 (iii) 25 titre 1 1× × Award 1 mark for the correct calculation, with marking [1] Award 1 mark for the answer given to 3 or 4 significant figures in each answer in calculation [1] (iv) ±0.1 in 10 cm3 is a larger % in uncertainty (than ±0.1 in 25 cm3) / % uncertainty in 25 cm3 pipette less than that of 10 cm3 pipette Award 1 mark for a qualitative argument [1] Award 1 mark for uncertainty in end point (1 drop) is less significant with larger pipette [1]

Page 4 Mark Scheme Syllabus Paper GCE AS LEVEL – October/November 2012 8780 04 © Cambridge International Examinations 2012 (b) (i) White precipitate formed addition of NaOH [1] (ii) White precipitate formed addition of NH3 [1] soluble in excess in BOTH [1] (iii) Zinc/Zn2+ [1] White precipitate with BOTH NaOH and NH3 and soluble in excess of BOTH [1] [TOTAL: 15]