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CIE Jun 2014 v5 Paper 3 Q1
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![PMT Limewater is a saturated solution of calcium hydroxide. A sample of limewater was diluted to produce solution FA 1. You are to determine the concentration of calcium hydroxide, Ca(OH)2, in FA 1 by titration with hydrochloric acid, HCl, which you willrst dilute. The equation for the reaction between calcium hydroxide and hydrochloric acid is given below. Ca(OH)2(aq) + 2HCl (aq)CaCl 2(aq) + 2H2O(l) FA 1 is aqueous calcium hydroxide, Ca(OH)2. FA 2 is 0.500 mol dm3 hydrochloric acid, HCl. methyl orange indicator (a) Method Read through the method before starting any practical work. (i) DilutionFill the burette with FA 2. Run between 24.00 and 26.00 cm3 of FA 2 into the 250 cm3 volumetric flask. Record your burette readings and the volume used in the space below. Make up the solution to 250 cm3 with distilled water and shake the flask to ensure thorough mixing. This solution is FA 3. volume of 0.500 mol dm3 HCl used =cm3 (ii) TitrationEmpty and rinse the burette. Fill the burette with FA 3. Pipette 25.0 cm3 of FA 1 into a conical flask. Add a few drops of methyl orange indicator. Perform a rough titration and record your burette readings in the space below. The rough titre iscm3.UCLES 2014 9701/35/M/J/14<br />
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 FA 3 added in each accurate titration. PMT II III IV VI VII VIII [8] (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 1 requiredcm3 of FA 3. [1]UCLES 2014 9701/35/M/J/14 [Turn over<br />
(c) Calculations Show your working and appropriate signi cantgures in thenal answer to each step of your calculations. (i) Use your volume of FA 2 from (a)(i) to calculate the concentration of FA 3. PMT (ii) Use your answer to (c)(i) and the value calculated in (b) to calculate the number of moles of hydrochloric acid used to neutralise 25.0 cm3 of FA 1. concentration of FA 3 =mol dm3 (iii) Use your answer to (c)(ii) to calculate the number of moles of calcium hydroxide in 25.0 cm3 of FA 1. moles of HCl =mol (iv) Use your answer to (c)(iii) to calculate the concentration, in mol dm3, of calcium hydroxide in FA 1. moles of Ca(OH)2 =mol II III IV concentration of Ca(OH)2 =mol dm3 [5]UCLES 2014 9701/35/M/J/14<br />
PMT (d) (i) The maximum error in a single burette reading is 0.05 cm3. When making up the diluted acid, FA 3, a student recorded that 24.80 cm3 of FA 2 was used. What are the smallest and largest possible volumes of acid that were run into the volumetricask? smallest volume used =cm3 largest volume used =cm3 (ii) If the actual volume of acid added had been less than 24.80 cm3, how would the value the student calculated for the concentration of Ca(OH)2 in (c)(iv) compare to the true value? Explain your answer.[2] (e) If a sample of limewater is left open to the air, the concentration of calcium hydroxide decreases. Explain why.[1] [Total: 17]UCLES 2014 9701/35/M/J/14 [Turn over<br />](https://learnah.org/wp-content/uploads/2018/08/June_2014_v5_QP_-_Paper_3_CIE_Chemistry_A-level_1-0.jpg)
![Page 2 Mark Scheme GCE AS/A LEVELMay/June 2014 Syllabus 9701 Paper 35 Question Sections Indicative material Mark Total (a) MMO Collection I Burette readings and correct volume given for dilution and volume between 24.00 and 26.00 cm3 PDO Layout PDO Recording MMO Decisions II 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) III Appropriate headings and units for accurate titration. and volume FA 3 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/FA 1 used/added (but not difference) IV 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) 50(.00) is used as an initial burette reading V Has two uncorrected, accurate titres within 0.1 cm3 Do not consider the rough even if ticked. Do not award this mark if having performed two titres within 0.1 cm3 a further titration is performed which is more than 0.10 cm3 from the closer of the initial two titres, unless a further titration, within 0.1 cm3 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 cm3. Check and correct subtractions in the dilution and titre tables. Examiner then selects the best titre using the hierarchy: two identical; titres within 0.05 cm3; titres within 0.1 cm3; etc. Candidate scaled titre = Cand vol dilutedCand mean titre/Sup vol diluted Examiner compares candidate scaled titre with Supervisors titre. (a) MMO Quality VI, VII and VIII Award VI, VII and VIII for0.20 cm3 Award VI and VII for 0.20 cm3 <0.40 cm3 Award VI only for a difference of 0.40 <0.60 cm3 If the best titres are0.50 cm3 apart cancel one of the Q marks. [8]Cambridge International Examinations 2014<br />
Page 3 Mark Scheme GCE AS/A LEVELMay/June 2014 Syllabus 9701 Paper 35 Question Sections Indicative material (b) ACE Interpretation Candidate must average two (or more) titres that are all 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 evaluates 0.500vol diluted in (i) II Correctly calculates (i)250 (b) 1000 in (ii) III Correctly calculates (ii)2 in (iii) IV Correctly calculates (iii)1000 25 in (iv) Mark Total 1 1 [1] [5] [2] [1] PDO Display V All answers given to 3 or 4 sf minimum 3 steps attempted to access this mark ACE Interpretation Conclusion (i) smallest = 24.70, largest = 24.90 (ii) lower conc FA 3 leads to greater titre therefore greater conc. of Ca(OH)2 ACE Conclusion limewater reacts with carbon dioxide in air (d) (e) Qn 1 Total [17]Cambridge International Examinations 2014<br />](https://learnah.org/wp-content/uploads/2018/08/June_2014_v5_MS_-_Paper_3_CIE_Chemistry_A-level_1-0.jpg)
