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CIE Nov 2013 v3 Paper 3 Q1
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![Examiners For Use In this experiment you are to determine the relative formula mass of an iron(II) salt by titration with potassium manganate(VII). FA 1 is the iron(II) salt. FA 2 is 0.0200 mol dm3 potassium manganate(VII), KMnO4. FA 3 is dilute sulfuric acid, H2SO4. (a) Method Preparing a solution of FA 1Weigh the 250 cm3 beaker and record the mass in the space below. Add all the FA 1 provided to the beaker. Weigh the beaker with FA 1 and record the mass. Calculate the mass of FA 1 used and record this in the space below. Use a measuring cylinder to add approximately 100 cm3 of FA 3 to the beaker. Stir until all the solid has dissolved. Transfer the solution into the 250 cm3 volumetric (graduated) flask labelled FA 4. 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 the iron(II) salt is FA 4. TitrationPipette 25.0 cm3 of FA 4 into a conical flask.Use a measuring cylinder to add 20 cm3 of FA 3 to the flask.Fill the burette with FA 2.Titrate FA 4 with FA 2 until the solution changes to a permanent pink colour.Perform a rough titration and record your burette readings in the space below. The rough titre iscm3.UCLES 2013 9701/33/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 FA 2 added in each accurate titration. Examiners For Use II III IV VI VII [7] (b) From your accurate titration results, obtain a suitable value to be used in your calculations. Show clearly how you have obtained this value. 25.0 cm3 of FA 4 requiredcm3 of FA 2 [1]UCLES 2013 9701/33/O/N/13 [Turn over<br />
(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 potassium manganate(VII) present in the volume of FA 2 calculated in (b). moles of KMnO4 =mol (ii) The half-equation for the reduction of a manganate(VII) ion is: MnO4+ 8H+ + 5eMn2+ + 4H2O Give the half-equation for the oxidation of an iron(II) ion to an iron(III) ion.Therefore, 1 mole of manganate(VII) ions reacts with 5 moles of iron(II) ions. (iii) Calculate the number of moles of iron(II) ions present in 25.0 cm3 of solution FA 4. (iv) Calculate the number of moles of iron(II) ions present in 250 cm3 of solution FA 4. moles of Fe2+ in 25.0 cm3 of FA 4 =mol moles of Fe2+ in 250 cm3 of FA 4 =mol (v) In 1 mole of the iron(II) salt, FA 1, there is 1 mole of iron(II) ions. Use the mass of FA 1 you weighed out to calculate the relative formula mass of the iron(II) salt. relative formula mass =[5]UCLES 2013 9701/33/O/N/13 Examiners For Use II III IV<br />
Examiners For Use (d) (i) A 25 cm3 pipette is accurate to 0.06 cm3. Calculate the maximum percentage error when the pipette was used to measure solution FA 4. (ii) State the maximum error in the mass of the 250 cm3 beaker that you recorded in (a). percentage error in measuring FA 4 =% maximum error =g (iii) Calculate the maximum percentage error in the mass of FA 1 used in (a). maximum percentage error =% [2] [Total: 15]UCLES 2013 9701/33/O/N/13 [Turn over<br />](https://learnah.org/wp-content/uploads/2018/08/November_2013_v3_QP_-_Paper_3_CIE_Chemistry_A-level_1-0.jpg)
![Page 2 Mark Scheme Syllabus Paper GCE A LEVELOctober/November 2013 9701 33 Question Sections Indicative material Mark Total PMT (a) PDO The following data must be given Layoutmass of solid used (or both weighings) volume for rough titre (or both readings) initial and final readings for two (or more) accurate titrations. PDO II Appropriate headings for all data given in Recording weighing and accurate titration tables and g and cm units.mass/weight (of) beaker (empty)mass/weight (of) beaker + FA 1/solid initial/start (burette) reading/volume final/end (burette) reading/volume titre or volume/FA 2 used/added unit: /cm or (cm ) or in cm or cm for each volume If g and/or cm units are not given in the heading, every entry in the table must have the correct unit. PDO III All accurate burette readings (including 0.00) Recording are to the nearest 0.05 cm The need to record to 0.05 applies only to the burette readings and not to the recorded titres. Do not award this mark if: 50(.00) is used as an initial burette reading ormore than one final burette reading is 50.(00) or any burette reading is greater than 50.(00). MMO IV There are two uncorrected accurate titres within Decision 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 , a further titration is performed which is more than 0.10 cm from the closer of the initial two titres, unless a further titration, 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 0) are given to zero dp.Cambridge International Examinations 2013<br />
PMT Page 3 Mark Scheme Syllabus Paper GCE A LEVELOctober/November 2013 9701 33 Question Sections Indicative material Mark Total (a) MMO Award V, VI and VII if0.03 (cm ) i.e. three Q (cont) Quality marks. Award V and VI if 0.03 <0.06 i.e. two Q marks. Award V, only, if 0.06 <0.10 i.e. one Q mark. Spread penalty: if the two best (corrected) titres used by the Examiner were0.50 cm apart, cancel one Q mark. [7] (b) MMO Check mean titre is correctly calculated from clearly Decision selected values (ticks or working).Candidate must average two (or more) titres where the total spread is0.20 cmWorking must be shown or ticks must be put next to the two (or more) accurate readings selected.The mean should normally be quoted to 2 dp rounded to the nearest 0.01. [e.g. 26.667 must be rounded to 26.67] Two special cases where the mean may not be to 2 dp: allow mean to 3 dp only for 0.025 or 0.075 e.g. 26.325; allow mean 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 incorrect.] Do not award this mark if: the rough titre was used to calculate the mean; candidate carried out only 1 accurate titration; [1] 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. (c) (i) ACE I Correctly calculates Interpretation No. of moles of KMnO4 = 0.0200 x (b) /1000 (ii) ACE II Fe Fe + e / 5Fe 5Fe + 5e 2+ 3+ 2+ 3+ Conclusion (iii) PDO III Correct working shown in (iii) and (iv). + (iv) Display The answer to (i) should be multiplied by 5 to give (iii). The answer to (iii) should be multiplied by 10 to give (iv). (v) ACE IV Correct calculation of relative formula mass. Interpretation Mr = correct mass of FA 1 used /answer to (iv)Cambridge International Examinations 2013<br />
PMT Page 4 Mark Scheme Syllabus Paper GCE A LEVELOctober/November 2013 9701 33 Question Sections Indicative material Mark Total (v) PDO V All answers are quoted to 3 or 4 significant (cont) Display figures. A minimum of three answers is needed to qualify. (d) (i) ACE % error for pipette = /25100 = 0.24% (or 0.06 Interpretation 0.240%) (ii) ACE + (iii) Interpretation If balance displays to 1 decimal place: error in balance reading is 0.05 g or 0.1(0) g. If balance displays to 2 decimal places: error in balance reading is 0.005 g or 0.01 g. If balance displays to 3 decimal places: error in balance reading is 0.0005 g or 0.001 g. % error = 2 balance error (above) /mass of FA 1 used100 Correct answer is not required, but if the100 [5] factor was omitted, a correctly calculated % error [2] answer scores the mark. [Total: 15] (a) MMO Collection The masses of FA 5 used by the candidate were between 2.02.4 g (expt 1) and 1.51.9 g (expt 2). PDO II Suitable headings for a table or list, shown Display completely for at least one experiment carried out. If 2 experiments, all headings must be correct. (mass of) empty crucible (mass of) crucible + FA 5 (mass of) crucible + residue / FA 5 after heating (mass of) residue (owtte) mass lost or (mass of) water lost. and unit was given covering every weighing; Unit: /g or (g) or in grams or g following each weighing PDO III Records all weighings consistently to at least Recording 1 dp. A minimum of three weighings are needed. Accuracy (Q) marks for gravimetric experiment3 marks available Examiner checks working for mass of residue and mass of water and expresses the mass of hydrated solid ratio /mass of water to 2 dp for each experiment. The expected ratio = /36 = 6.78. 244Cambridge International Examinations 2013<br />](https://learnah.org/wp-content/uploads/2018/08/November_2013_v3_MS_-_Paper_3_CIE_Chemistry_A-level_1-0.jpg)
