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CIE Nov 2013 v6 Paper 3 Q1
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![Examiners For Use In this experiment you are to determine the concentration of aqueous potassium manganate(VII), FB 3, by titration. In the titration potassium manganate(VII) isrst reacted with acidi ed potassium iodide to produce iodine. The amount of iodine formed is then determined by titrating the mixture with sodium thiosulfate. FB 1 is hydrated sodium thiosulfate, Na2S2O3.5H2O. FB 2 is dilute sulfuric acid, H2SO4. FB 3 is aqueous potassium manganate(VII), KMnO4. FB 4 is aqueous potassium iodide, KI. starch indicator (a) Method Preparing a solution of FB 1Weigh the 250 cm3 beaker and record the mass in the space below. Add all the FB 1 to the beaker. Weigh the beaker with FB 1 and record the mass. Calculate the mass of FB 1 used and record this in the space below. Add approximately 100 cm3 of distilled water to the beaker. Stir until all the solid has dissolved. Transfer the solution into the 250 cm3 volumetric (graduated) flask labelled FB 5. Wash out the beaker thoroughly using distilled water and add the washings to the volumetric flask. Make the solution up to the mark using distilled water. Shake the flask thoroughly to mix the solution before using it for your titrations. This solution of sodium thiosulfate is FB 5. TitrationUse the measuring cylinder to add 20 cm3 of FB 2 to a conical flask. Use the measuring cylinder to add 10 cm3 of FB 4 to the same flask. Pipette 25.0 cm3 of FB 3 into the same flask. The colour of the mixture is caused by iodine. Fill the burette with FB 5. Begin each titration without adding the starch indicator. Add 10 drops of starch indicator when the colour of the mixture becomes (pale) yellow. The end-point is when the blue-black colour caused by the starch disappears. Perform a rough titration and record your burette readings in the space below. The rough titre iscm3.UCLES 2013 9701/36/O/N/13<br />
Carry out as many accurate titrations as you think necessary to obtain consistent results. Make sure any recorded results show the precision of your practical work. Record in a suitable form below all of your burette readings and the volume of FB 5 added in each accurate titration. Examiners For Use II III IV VI VII (b) From your accurate titration results, obtain a suitable value to be used in your calculations. Show clearly how you have obtained this value. [7] suitable value =cm3 of FB 5 [1] (c) Calculations Show your working and appropriate signi cantgures in thenal answer to each step of your calculations. (i) Calculate the number of moles of sodium thiosulfate, FB 1, that were weighed out. The relative formula mass of hydrated sodium thiosulfate is 248.2. moles of sodium thiosulfate =mol (ii) Calculate the number of moles of sodium thiosulfate that were present in the volume of FB 5 calculated in (b). moles of sodium thiosulfate =molUCLES 2013 9701/36/O/N/13 [Turn over<br />
Examiners For Use II III IV (iii) Iodine produced by the reaction in the conicalask reacts with sodium thiosulfate. Use the equation below to calculate the number of moles of iodine that reacted with sodium thiosulfate in (ii). I2 + 2Na2S2O32NaI + Na2S4O6 moles of I2 =mol (iv) The iodine is produced as a result of the oxidation of iodide ions in potassium iodide, FB 4, by potassium manganate(VII), FB 3. The ionic equation for this reaction is 2MnO4+ 16H+ + 10I2Mn2+ + 5I2 + 8H2O Calculate the number of moles of potassium manganate(VII), KMnO4, that reacted to produce the iodine in (iii). (v) Calculate the concentration of potassium manganate(VII), in g dm3, in FB 3. (Ar : O, 16.0 ; K, 39.1; Mn, 54.9) moles of KMnO4 =mol concentration of KMnO4 =g dm3 [5] (d) (i) State the maximum error in any single reading of the burette. (ii) Calculate the maximum percentage error in volume of FB 5 in yourrst accurate titre. maximum error =cm3 maximum percentage error =% [1] [Total: 14]UCLES 2013 9701/36/O/N/13<br />](https://learnah.org/wp-content/uploads/2018/08/November_2013_v6_QP_-_Paper_3_CIE_Chemistry_A-level_1-0.jpg)
![PMT Page 2 Mark Scheme Syllabus Paper GCE A LEVELOctober/November 2013 9701 36 Question Sections Indicative material Mark Total 1 (a) PDO I The following data are given layoutmass of solid used (or both weighings)volume used in rough titre (or both readings)initial and final readings for two (or more) accurate titrations PDO II Acceptable/appropriate headings for all data given in recording weighing and accurate titration tables and g and cm units.mass/weight of beaker (empty)mass of beaker + FB 1/solidmass solid/FB1initial/start/first (burette) reading/volumefinal/end/second (burette) reading/volumetitre or volume used/added/FB 5 added (but not difference or change in volume)unit:/cm or (cm ) or in cm or cm If g/cm units are not given in the heading, every entry in the table must have the correct unit. PDO recording MMO decision III All accurate burette readings are to the nearest 0.05 cm The need to record to 0.05 only applies to the burette readings, including 0.00 cm (if this was the initial reading), but it does not apply to the titre. Do not award this mark if:50(.00) is used as an initial burette readingmore than one final burette reading is 50.(00)any burette reading is greater than 50.(00). IV There are two uncorrected accurate titres within 0.10 cm Do not include a reading if it is labelled rough. Do not award this mark if, having performed two titres within 0.1 cm more than 0.10 cm , a further titration is performed which is from the closer of the initial two titres, unless further titrations, within 0.1 cm of any other, has also been carried out. Do not award the mark if any accurate burette readings (apart from initial zero) are given as integers. MMO quality Examiner calculates mean titremass FB 1 for candidate and Supervisor. Award V, VI and VII if2 (g cm Award V and VI if 2 <3 Award V, only, if 3 <5. Spread penalty: if two best titres used by the Examiner are0.50 cm apart, cancel one Q mark.Cambridge International Examinations 2013 [7]<br />
Page 3 Mark Scheme Syllabus Paper GCE A LEVELOctober/November 2013 9701 36 (b) MMO Candidate calculates the mean correctly. decision Candidate must take the average two (or more) titres where the total spread is0.2 cm Working must be shown or ticks must be put next to the accurate titres selected. The mean should normally be quoted to 2 dp, rounded to nearest 0.01 cm rounded to 26.67 not 26.65 cm rounded to 26.68 not 26.70 cm . Example 26.667 cm must be , 26.675 cm must be Two special cases, where the mean may not be to 2 dp: Allow mean expressed to 3 dp, only for 0.025 or 0.075. Allow mean if expressed to 1 dp if all accurate burette readings were given to 1 dp (ignoring initial given as 0) and the mean is exactly correct e.g. 26.0 and 26.2 = 26.1 is correct but 26.0 and 26.1 = 26.1 is wrongshould be 26.05. Do not award this mark if:The rough titre was used to calculate the mean.The candidate did only one accurate titration.Burette readings were incorrectly subtracted to obtain any of the accurate titre values.All burette readings (resulting in titre values used in calculation of mean) are integers. Note: the candidates mean will sometimes be marked correct even if it is different from the mean calculated by the Examiner for the purpose of assessing accuracy. (c) ACE I Correctly calculates moles of Na2S2O3 weighed in (i) interpretation = mass of FB1 used 248.2 II Correct expression for moles of Na2S2O3 used in (ii) = answer (i)mean titre 250 PMT [1] III Correct calculations/expression in (iii) and (iv) (iii) : no moles of I 2 = 0.5(ii) PDO display IV Correct expression in (v) Mass = answer (iv)40 158(.0) ( 40 may be shown as1000/25) PDO display V All quoted answers are given to 3 or 4 significant figures. (minimum of three answers) [5]Cambridge International Examinations 2013<br />
Page 4 Mark Scheme Syllabus Paper GCE A LEVELOctober/November 2013 9701 36 PMT 1 (d) ACE error = 0.05 cm in (i) interpretation and 2 (a) [1] % error in volume of FB 5 =100 in vol of 5FB used 0.05 (ii) MMO collection I The masses of FB 6 used by the candidate were between 2.02.4 g (expt 1) and 2.52.9 g (expt 2). PDO II Suitable headings for a table or list, shown completely display for at least one experiment. If 2 experiments, all headings must be correct.(mass of) empty crucible(mass of) crucible + FB 6(mass of) crucible + residue/FB 6 after heatingmass (water) lost or mass anhydrous remaining and unit covering every weighing. Unit/g or (g) or in grams or g following each weighing. PDO recording MMO quality III Records all balance readings consistently to at least 1 dp A minimum of three weighings are needed. of mass hydrated salt Examiner calculates for each of mass water experiment. Award IV if the ratio in expt 1 is between 0.95 and 1.15. Award V If the ratio in expt 2 is between 0.95 and 1.15. Award VI If the ratio in both of experiments 1 and 2 is between 0.85 and 1.25. [Total: 14] [6] 2 (b) MMO (i) An appropriate choice of the more accurate quality experiment, and justification of choice. Three possibilities:Experiment 2 uses a larger mass and has a greater percentage accuracy.A reference to either experiment spitting or frothing during heating is a valid reason for nominating the other experiment. heating.Experiment 1 as smaller mass takes less ACE (ii) Correctly calculates number of moles of water interpretation = mass of water lost 18 Candidate must use the mass loss for the Ans to 24 sf choice is expressed in (i), this should be expt 2.) Allow (l) for water. experiment thought to be more accurate. (If no ACE (iii) MSO4.7H2O(s) MSO4(s) + 7H2O(g) conclusionCambridge International Examinations 2013<br />](https://learnah.org/wp-content/uploads/2018/08/November_2013_v6_MS_-_Paper_3_CIE_Chemistry_A-level_1-0.jpg)
