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CIE Nov 2014 v5 Paper 3 Q1
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![In this experiment you are to determine x in the formula of hydrated sodium carbonate, Na2CO3.xH2O, by titration. PMT FA 1 is aqueous sodium carbonate, Na2CO3, containing 150.0 g of solid Na2CO3.xH2O in each dm3 of solution. FA 2 is 0.110 mol dm3 nitric acid, HNO3. methyl orange indicator (a) Method Diluting the solution of FA 1Pipette 25.0 cm3 of FA 1 into the 250 cm3 volumetric (graduated) 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 carbonate is FA 3. Rinse the pipette with distilled water. TitrationPipette 25.0 cm3 of FA 3 into a conical flask. Fill the burette with FA 2. Add several drops of methyl orange indicator to the conical flask. Carry out a rough titration and record your burette readings in the space below.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. The rough titre iscm3. II III IV VI VII [7]UCLES 2014 9701/35/O/N/14<br />
(b) From your accurate titration results, obtain a suitable value to be used in your calculations. Show clearly how you have obtained this value. PMT volume of FA 2 =cm3 [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 nitric acid in the volume of FA 2 calculated in (b). moles of HNO3 =mol (ii) Complete the equation below and include the missing state symbols. Na2CO3(aq) + HNO3(aq)NaNO3 + CO2 + H2O (iii) Calculate the number of moles of sodium carbonate in 25.0 cm3 of solution FA 3. (iv) Calculate the number of moles of sodium carbonate in 250.0 cm3 of solution FA 3. moles of Na2CO3 in 25.0 cm3 of FA 3 =mol moles of Na2CO3 in 250.0 cm3 of FA 3 =molUCLES 2014 9701/35/O/N/14 [Turn over<br />
(v) Use the information on page 2 and your answer to (iv) to calculate the relative formula mass, Mr, of hydrated sodium carbonate, Na2CO3.xH2O. PMT (vi) Calculate the value of x in Na2CO3.xH2O. Give your answer to the nearest whole number. [Ar: H, 1.0; C, 12.0; O, 16.0; Na, 23.0] Mr of Na2CO3.xH2O =x =[6] (d) (i) State the maximum error in any single reading of the burette. (ii) Calculate the maximum percentage error in the volume of FA 2 in yourrst accurate titre. maximum error =cm3 maximum percentage error = % [1] [Total: 15]UCLES 2014 9701/35/O/N/14<br />](https://learnah.org/wp-content/uploads/2018/08/November_2014_v5_QP_-_Paper_3_CIE_Chemistry_A-level_1-0.jpg)
![Page 2 Cambridge International AS / A LevelOctober / November 2014 Mark Scheme Syllabus Paper 9701 35 Question Indicative material Mark Total PMT (a) Initial and final readings and titre value given for rough titre and initial and final readings for two (or more) accurate titrations (minimum of 22 box) II Appropriate headings and units for accurate titration and volume FA 2 added recorded for each accurate titre. Headings should match readings.initial / start (burette) reading / volume (not V or vol)final / end (burette) reading / volumetitre or volume / FA 2 and used / added (but not difference) unit: / cm for each entry ) or in cm or (cm or cm III All accurate burette readings recorded to 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 readingmore than one final burette reading is 50.(00)any burette reading is greater than 50(.00) IV Has two uncorrected, accurate titres within 0.1 cm Do not consider the rough even if ticked. Do not award this mark if having performed two titres within 0.10 cm 0.10 cm titration, within 0.10 cm a further titration is performed which is more than from the closer of the initial two titres, unless a further of any other titration has also been carried out. Do not award the mark if any accurate burette readings (apart from initial 0) are given to zero dp. Round any burette readings to the nearest 0.05 cm Check and correct subtractions for Supervisor and candidate. Examiner then selects the best titre using the hierarchy: two (or more) identical; then two (or more) within 0.05 cm then two (or more) within 0.1 cm ; etc. Examiner compares candidate mean titre with Supervisor mean titre. V, VI and VIIY 0.40 cm Award V, VI and VII for a difference from Supervisor, 0.20 cm Award V and VI for 0.20 cm Award V only for a difference of 0.40Y 0.60 cm Spread penalty: if the best titres are0.50 cm the Q marks. apart cancel one of [7]Cambridge International Examinations 2014<br />
Page 3 Cambridge International AS / A LevelOctober / November 2014 Mark Scheme Syllabus Paper 9701 35 PMT (b) Calculation of meanCandidate must average two (or more) titres where the total spread is 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, and be correctly rounded to the nearest 0.01 cm 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 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. Note: the candidates mean will sometimes be marked as correct even if it is different from the mean calculated by the examiner for the purpose of assessing accuracy. [1] (c) (i) 0.110mean titre Correct working shown in step (i) 1000 (ii) Balanced equation with added state symbols Na2CO3(aq) + 2HNO3(aq)2NaNO3(aq) + CO2(g) + H2O(l) (iii) and (iv) Correctly calculates moles Na2CO3 (in 25 cm ) =(i) and moles Na2CO3 (in 250 cm ) = 10(iii) (v) Correctly calculates Mr = 150.0(iv) 10 or (3.75 / (iv)) Theoretical answer = 286Cambridge International Examinations 2014<br />
PMT Page 4 Cambridge International AS / A LevelOctober / November 2014 Mark Scheme Syllabus Paper 9701 35 (vi) Correctly calculates x to the nearest integer. (v) 106 x = 18 Allow ecf Answers to (i), (iii), (iv) and (v) shown to 3 or 4 sf. Minimum of 3 answers needed to qualify for the mark. All answers given must have correct sf. (d) 0.05 cm (i) and (ii) % = 0.1 100 accurate titre [6] Allow any accurate titre to be used (but not the mean). [1] (a) Correct headings and unitsmass of container and FA 4 / solidmass of container (empty / plus residue) [Total: 15]mass of FA 4 (used) initial temperature / thermometer readingmaximum / highest temperature / final / thermometer reading / temp. / T temperature rise (a) and (c) All four weighings shown to same number of dp (a) Check and correct subtractions of Supervisor and candidate. Calculate difference between (corrected) candidates and Supervisors temperature rise, . Award if1.0 C If T is6.5 C only award if0.5 C. (b) (i) Correctly calculates: energy produced = 254.2temp rise (to 24 sf) (ii) Correctly calculates moles of FA 4 = mass used 106 Answer must be expressed to 24 sf [3]Cambridge International Examinations 2014<br />](https://learnah.org/wp-content/uploads/2018/08/November_2014_v5_MS_-_Paper_3_CIE_Chemistry_A-level_1-0.jpg)
