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CIE Nov 2013 v4 Paper 3 Q1
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![Examiners For Use FB 1 is 0.125 mol dm3 hydrochloric acid, HCl. FB 2 is an aqueous solution containing sodium hydroxide, NaOH, and sodium carbonate, Na2CO3. bromophenol blue acid-base indicator By carrying out titrations, you are to determine the percentage by mass of sodium carbonate in the mixture of sodium hydroxide and sodium carbonate in solution FB 2. (a) TitrationFill a burette with FB 1. Pipette 25.0 cm3 of FB 2 into a conical flask. Add a few drops of bromophenol blue indicator. Titrate the mixture in the flask with FB 1 until the blue-violet colour of the solution changes to yellow. Perform a rough titration and record your burette readings in the space below. The rough titre is . cm3. Carry out as many accurate titrations as you think necessary to obtain consistent results. Make certain 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 1 added in each accurate titration. 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 FB 2 requiredcm3 of FB 1 [1]UCLES 2013 9701/34/O/N/13<br />
Examiners For Use (c) Calculations When the titrations were repeated using phenolphthalein as the indicator, 25.0 cm3 of FB 2 required 23.25 cm3 of FB 1. The following explains why different results are obtained using two different indicators. When phenolphthalein is used as the indicator, the following reactions have taken place at the end-point of the titration. 1. NaOH(aq) + HCl (aq)NaCl (aq) + H2O(l) 2. Na2CO3(aq) + HCl (aq)NaCl (aq) + NaHCO3(aq) When bromophenol blue is used as the indicator in (a), the following reactions have taken place at the end-point of the titration. 1. NaOH(aq) + HCl (aq)NaCl (aq) + H2O(l) 2. Na2CO3(aq) + HCl (aq)NaCl (aq) + NaHCO3(aq) 3. NaHCO3(aq) + HCl (aq)NaCl (aq) + CO2(g) + H2O(l) Show your working and use appropriate signi cantgures in thenal answer to all steps of your calculations. (i) Calculate the number of moles of hydrochloric acid in the volume of FB 1 calculated in (b). (ii) Calculate the number of moles of hydrochloric acid in 23.25 cm3 of FB 1. moles of HCl in volume in (b) =mol (iii) Use the following formula to calculate the number of moles of hydrochloric acid that react with the Na2CO3 in the titration using phenolphthalein indicator. moles of HCl in 23.25 cm3 =mol moles HCl = answer (i)answer (ii) =molUCLES 2013 9701/34/O/N/13 [Turn over<br />
Examiners For Use II III IV VI (iv) Use your answer to (iii) to calculate the mass of sodium carbonate present in 25.0 cm3 of FB 2. [Ar : C, 12.0; O, 16.0; Na, 23.0] mass of Na2CO3 in 25.0 cm3 FB 2 =g (v) The overall equation for the reaction of Na2CO3 with HCl when bromophenol blue is used as indicator is given below. Na2CO3(aq) + 2HCl (aq)2NaCl (aq) + CO2(g) + H2O(l) Calculate the number of moles of HCl that reacted with the Na2CO3 in the above equation in 25.0 cm3 of FB 2. (vi) Use your answers to (i) and (v) to calculate the mass of sodium hydroxide in 25.0 cm3 of FB 2. [Ar : H, 1.0; O, 16.0; Na, 23.0] moles of HCl =mol (vii) Calculate the percentage by mass of sodium carbonate in the mixture of sodium hydroxide and sodium carbonate in FB 2. mass of NaOH =g FB 2 contains% by mass Na2CO3 [6] [Total: 14]UCLES 2013 9701/34/O/N/13<br />](https://learnah.org/wp-content/uploads/2018/08/November_2013_v4_QP_-_Paper_3_CIE_Chemistry_A-level_1-0.jpg)
![Page 2 Mark Scheme Syllabus Paper GCE A LEVELOctober/November 2013 9701 34 Question Sections Indicative material Mark Total (a) MMO Initial and final readings and titre value given for Collection rough titre and initial and final readings for two (or more) accurate titrations (minimum of 22 box) PDO II Appropriate headings and units for all accurate data Layout and volume FB 1 added recorded for each accurate titre. Headings should match readings. initial/start (burette) reading/volume final/end (burette) reading/volume titre or volume/FB 1 used/added (but not difference) unit: /cm or (cm ) or in cm or cm for each entry PDO III All accurate burette readings recorded to 0.05 cm Recording 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 readingmore than one final burette reading is 50.(00) any burette reading is greater than 50.(00). MMO IV Has two uncorrected accurate titres within 0.1 cm Decisions 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 />
Page 3 Mark Scheme Syllabus Paper GCE A LEVELOctober/November 2013 9701 34 Question Sections Indicative material Mark Total (a) For assessment of accuracy (Q) marks, an Examiner rounds any (cont) burette readings to the nearest 0.05 cm , checks subtractions and then selects the best titres using the hierarchy: two (or more) accurate identical titres (ignoring any that are labelled rough), then two (or more) accurate titres within 0.05 cm , then two (or more) accurate titres within 0.10 cm , etc. These best titres are used to calculate the mean titre, to nearest 0.01 cm MMO Quality Award V, VI and VII forY 0.20 cm Award V and VI for 0.20 <Y 0.30 cm Award V for 0.30 <Y 0.50 cm Spread penalty: if the two best titres used by the Examiner are [ 0.50 cm apart, cancel one Q mark. If Supervisor titre Y 15 cm then tolerances are 0.10, 0.20 and 0.30 cm [7] (b) MMO Check mean titre is correctly calculated from clearly Decisions selected values (ticks or working).Candidate must average two (or more) titres where the total spread is Y 0.20 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 eg 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; burette readings were incorrectly subtracted to obtain any of the accurate titre values; [1] all burette readings (resulting in titre values used in calculation of mean) are integers.Cambridge International Examinations 2013<br />
Page 4 Mark Scheme Syllabus Paper GCE A LEVELOctober/November 2013 9701 34 Question Sections Indicative material Mark Total 1 (c) (i) ACE (ii) Interpretation I Correctly calculates answer to in (i) (b) 0.125 1000 (iii) and 23.250.125 1000 0.002906 (0.00291) in (ii) II Correctly calculates answer to (iii) (ignore sf). If (i) < (ii) then answer must be negative. (iv) (v) PDO Display III Shows use of (iii)106 in (iv) and2 in (v). (This should be (iii)2 but allow (iv)2.) (vi) ACE Interpretation IV Correct method [(i)(v)]40 in (vi) (vii) V Correct expression:100 in (vii) (iv) [(iv) (vi)] or correct answer PDO VI All quoted answers given to 3 or 4 significant Display figures except in (iii). (Minimum of 4 answers needed.) [6] [Total 14]Cambridge International Examinations 2013<br />](https://learnah.org/wp-content/uploads/2018/08/November_2013_v4_MS_-_Paper_3_CIE_Chemistry_A-level_1-0.jpg)
