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CIE Jun 2016 v1 Paper 3 Q2
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![In this experiment you will determine the concentration of the hydrochloric acid, FA 2, used in Question 1. You will first dilute the reaction mixture that you prepared in Question 1 and then titrate this diluted solution against sodium hydroxide, NaOH. PMT HCl (aq) + NaOH(aq)NaCl (aq) + H2O(l) FA 3 is 0.0400 mol dm3 sodium hydroxide, NaOH. methyl orange indicator (a) Method DilutionTransfer all the reaction mixture that you prepared in 1(a) from the 250 cm3 beaker to the 250 cm3 volumetric flask. Rinse the beaker with a little distilled water and add these washings to the volumetric flask. Fill the volumetric flask to the line with distilled water. Stopper the flask and shake it to ensure thorough mixing. Label this solution FA 4. TitrationFill the burette with FA 4. Use a pipette to transfer 25.0 cm3 of FA 3 into a conical flask. Add a few drops of methyl orange. Perform 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 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 4 added in each accurate titration. The rough titre iscm3. II III IV [4]UCLES 2016 9701/31/M/J/16<br />
(b) From your accurate titration results, obtain a suitable value for the volume of FA 4 to be used in your calculations. Show clearly how you obtained this value. PMT 25.0 cm3 of FA 3 requiredcm3 of FA 4. [1] (c) Calculations Show your working and appropriate significant figures in the final answer to each step of your calculations. (i) Calculate the number of moles of sodium hydroxide, NaOH, present in 25.0 cm3 of FA 3. (ii) Calculate the number of moles of hydrochloric acid, HCl, present in 250 cm3 of FA 4. moles of NaOH =mol (iii) Use your answers to 1(b)(i) and 1(b)(ii) to calculate the number of moles of HCl that reacted with FA 1 in the experiment you carried out in Question 1. moles of HCl in 250 cm3 of FA 4 =mol (iv) Use your answers to 2(c)(ii) and 2(c)(iii) to calculate the concentration of FA 2. moles of HCl that reacted with FA 1 =mol concentration of FA 2 =mol dm3 [5]UCLES 2016 9701/31/M/J/16 [Turn over<br />
PMT (d) (i) One of the sources of error in determining the concentration of FA 2 involves measuring volumes of solutions in both Questions 1 and 2. State which volume of solution that you have measured has the greatest percentage error. How could you have reduced this error?(ii) A student suggested that a greater mass of XCO3 should be used so that the average titre calculated in 2(b) would be a greater volume. Explain whether you agree with the student that this would lead to a greater volume for the average titre.[2] [Total: 12]UCLES 2016 9701/31/M/J/16<br />](https://learnah.org/wp-content/uploads/2018/08/June_2016_v1_QP_-_Paper_3_CIE_Chemistry_A-level_2-0.jpg)
![Page 3 Question (iii) Question 1 (a) Cambridge International AS/A LevelMay/June 2016 9701 31 Mark Scheme Syllabus Paper Indicative material Mark Total Any 1 fromAdd slowly / add a little at a timeUse a taller beaker (accept larger beaker) / use a conical [3] flaskUse less solidUse less concentrated acidUse lumps of solidUse cotton wool plugUse a lower temperature Initial and final readings and titre value for rough titre I and initial and final reading for two (or more) accurate titrations II Titre values recorded for accurate titrations and Appropriate headings for the accurate titration table and cm3 units.unit: / cm3 or (cm3) or in cm3 or cm3 (for each heading) initial / start burette reading / volume / value final / end burette and reading / volume / value titre or volume / FA4 and used / added III All accurate burette readings are recorded to nearest 0.05 cm3 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)there is only one accurate titration IV There are two uncorrected, accurate titres within 0.10 cm3Do 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 two initial titres, unless a further titration, within 0.10 cm3 of any other, has also been carried out.Do not award the mark if any accurate burette readings (apart from initial 0 cm3) are given to zero dp [15] [4]Cambridge International Examinations 2016<br />
Page 4 Question (b) Cambridge International AS/A LevelMay/June 2016 9701 31 Mark Scheme Syllabus Paper Indicative material Mark Total Candidate must take the average of two (or more) titres that are within a total spread of not more than 0.20 cm3. Working must be shown or ticks must be put next to the two (or more) accurate readings selected. The mean should 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 expressed to 3 dp only for 0.025 or 0.075 (e.g. 26.325)Allow mean if expressed 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 allowed) (e.g. 26.0 and 26.1 = 26.1 is incorrectshould be 26.05.) 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] [5] [2] [12] (c) (i) I Correctly calculates n(NaOH) = 0.001 (ii) II Shows use of 250 ( )( ) c i ) (iii) III Correctly calculates 21(b)(i) (iv) IV Shows use of 2(c)(ii) + 2(c)(iii) either as expression or correct calculation V Shows use of / 0.025(0) or40 or1000 / 25 (d) (i) States that the measuring cylinder / volume of FA2 has the greatest error and should be replaced by burette or pipette (ii) Student is correct / greater volume HCl used and greater mass would react with more HCl / would leave less HCl unreacted Question 2Cambridge International Examinations 2016<br />
Page 5 Question Cambridge International AS/A LevelMay/June 2016 9701 31 Mark Scheme Syllabus Paper Indicative material Mark Total FA5 is MnSO4 and NH4Cl; FA6 is propanone; FA7 is propanal; [2] [8] [1] [2] [13] (a) (i) Red litmus turns blue (then red) Condensation or sublimation / white smoke / white fumes (a) (ii) and (b) (i) / ammonium in 3(a)(ii) and Mn2+ + / manganese(II) in NH4 3(b)(i). (b) (i) Selects NaOH and NH3 Off-white / beige / light brown precipitate with both NaOH and NH3 Both precipitates turns brown / darkens (ii) white precipitate and insoluble in acid (iii) Selects AgNO3 / silver nitrate and NH3 / ammonia (c) (d) White precipitate and insoluble / partially soluble in ammonia Cannot see if precipitate dissolves in ammonia / Mn2+ causes (off-white) precipitate (so cannot be used to distinguish between halides). 2 and (NH4)2SO4 MnCl or MnSO4 and NH4Cl Both observations required FA6 no reaction / solution turns pink and FA7 turns colourless / decolourises the KMnO4 FA6 is either 2-methylpropan-2-ol or propanone as they cannot be oxidised (only 1 needed) and FA7 is propanal as it can be oxidised. Question 3Cambridge International Examinations 2016<br />](https://learnah.org/wp-content/uploads/2018/08/June_2016_v1_MS_-_Paper_3_CIE_Chemistry_A-level_2-0.jpg)
