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CIE Jun 2014 v2 Paper 3 Q1
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![Carbon dioxide in the atmosphere dissolves in rain water making it acidic. When this water passes through limestone containing calcium carbonate, it forms solutions of calcium hydrogen carbonate. PMT In this experiment, you will determine the concentration of hydrogen carbonate ions in a solution by titration with hydrochloric acid. FB 1 is 0.100 mol dm3 hydrochloric acid, HCl. FB 2 contains an unknown concentration of hydrogen carbonate ions, HCO3 methyl orange indicator . (a) MethodFill the burette with FB 1. Pipette 25.0 cm3 of FB 2 into a conical flask. Add a few drops of methyl orange indicator to the conical flask. Perform a rough titration and record your burette readings in the space below. The rough titre iscm3.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]UCLES 2014 9701/32/M/J/14<br />
(b) From your accurate titration results obtain a suitable value to be used in your calculations. Show clearly how you obtained this value. PMT 25.0 cm3 of FB 2 requiredcm3 of FB 1. [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 hydrochloric acid present in the volume of FB 1 calculated in (b). moles of HCl =mol (ii) Write the ionic equation for the reaction of FB 1 with FB 2.(iii) Calculate the concentration, in mol dm3, of hydrogen carbonate ions in FB 2. II concentration of HCO3in FB 2 =mol dm3 [2] [Total: 10]UCLES 2014 9701/32/M/J/14 [Turn over<br />](https://learnah.org/wp-content/uploads/2018/08/June_2014_v2_QP_-_Paper_3_CIE_Chemistry_A-level_1-0.jpg)
![Page 2 Mark Scheme GCE AS/A LEVELMay/June 2014 Syllabus 9701 Paper 32 Question Sections Indicative material Mark Total (a) PDO Layout I 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) PDO Recording MMO Decisions II Appropriate headings and units for all accurate data. and volume FB 1 added recorded for each accurate titre. Headings should match readings.unit: /cm3 or (cm3) or in cm3 or cm3 for each entry initial/start (burette) reading/volume final/end (burette) reading/volume titre or volume/FB 1 used/added (not difference) III All accurate burette readings recorded to 0.05 cm3. 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:more than one final burette reading is 50.(00)any burette reading is greater than 50.(00). 50(.00) is used as an initial burette reading IV Has two uncorrected, accurate titres within 0.1 cm3. Do not include a reading labelled rough. Do not award this mark if, having performed two titres within 0.1 cm3, a further titration is performed that is more than 0.1 cm3 from the closer of the two initial titres unless further titrations within 0.1 cm3 of any other have also been carried out. Do not award the mark if any accurate burette readings (apart from initial 0) are given to zero dp. All burette readings should be rounded to the nearest 0.05 cm3. Subtractions should be checked. The best titres should be selected using the hierarchy: two (or more) identical, then two (or more) within 0.05 cm3 , then two (or more) within 0.1 cm3, etc. Examiner compares candidate mean titre with Supervisor mean titre. (a) MMO Quality V, VI and VII Award V, VI and VII for a difference from Supervisor,0.20 cm3 Award V and VI for 0.20 <0.30 cm3 Award V only for 0.30 <0.50 cm3 Spread penalty: if the two best titres are0.50 cm3 apart cancel one of the Q marks. [7]Cambridge International Examinations 2014<br />
Page 3 Mark Scheme GCE AS/A LEVELMay/June 2014 Syllabus 9701 Paper 32 Question Sections Indicative material Mark Total (b) MMO Decisions Candidate must average two (or more) titres that are within 0.20 cm3. Working 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. 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. (c) ACE Interpretation I Correctly calculates (b) 0.100 1000 in (i) and gives ans (i)40 in (iii) (both answers to 3 or 4 sf) PDO Display II Gives correct equation in (ii) H+ + HCO3H2O + CO2 (allow H2CO3) Qn 1 Total [1] [2] 10Cambridge International Examinations 2014<br />](https://learnah.org/wp-content/uploads/2018/08/June_2014_v2_MS_-_Paper_3_CIE_Chemistry_A-level_1-0.jpg)
