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CIE Nov 2014 v4 Paper 3 Q1
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![Hydrogen peroxide, H2O2, is used in hair bleach and for skin therapies. In this experiment you will determine the concentration of a solution of hydrogen peroxide by titration with acidi ed potassium manganate(VII). PMT FB 1 is 0.0250 mol dm3 potassium manganate(VII), KMnO4. FB 2 is dilute sulfuric acid, H2SO4. FB 3 is aqueous hydrogen peroxide, H2O2. (a) Method Dilution of FB 3Pipette 25.0 cm3 of FB 3 into the volumetric (graduated) flask. Make the solution up to the mark using distilled water. Shake the flask thoroughly. This diluted solution of hydrogen peroxide is FB 4. TitrationFill the burette with FB 1. Pipette 10.0 cm3 of FB 4 into a conical flask. Use a measuring cylinder to add 25 cm3 of FB 2 into the same flask. Add FB 1 until a permanent pale pink colour is seen. 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 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 FB 1 added in each accurate titration. Keep solution FB 2 for use in Question 3 and solution FB 3 for use in Questions 2 and 3. II III IV VI VII [7]UCLES 2014 9701/34/O/N/14<br />
(b) From your accurate titration results, obtain a suitable value for the volume of FB 1 to be used in your calculations. Show clearly how you have obtained this value. PMT 10.0 cm3 of FB 4 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 potassium manganate(VII) present in the volume calculated in (b). moles of KMnO4 =mol (ii) Complete the equation below for the reaction of potassium manganate(VII) with hydrogen peroxide. State symbols are not required. KMnO4 + 5H2O2 + 3H2SO4K2SO4 + 2MnSO4 + H2O + 5O2 (iii) Use your answers to (i) and (ii) to calculate the number of moles of hydrogen peroxide used in each titration. (iv) Calculate the concentration of H2O2 in FB 4, in mol dm3. moles of H2O2 =mol (v) Calculate the concentration of H2O2 in FB 3, in mol dm3. concentration of H2O2 in FB 4 =mol dm3 concentration of H2O2 in FB 3 =mol dm3 [5]UCLES 2014 9701/34/O/N/14 [Total: 13] [Turn over<br />](https://learnah.org/wp-content/uploads/2018/08/November_2014_v4_QP_-_Paper_3_CIE_Chemistry_A-level_1-0.jpg)
![Page 2 Mark Scheme Syllabus Paper Cambridge International AS/A LevelOctober/November 2014 9701 34 Question (a) Indicative material Mark Total I The following data is showntwo burette readings for the rough titration titre for rough titration initial and final burette readings for two (or more) accurate titrations (i.e. 22 box) II Appropriate headings and units for accurate titration 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 and (burette) reading / volume final / end and (burette) reading / volume titre or volume / FB 1 and used / added III All accurate burette readings are to the nearest 0.05 cm3. The requirement to record to 0.05 applies to burette readings, including 0.00 cm3 (if this was the initial reading), but it does not apply to the titre. Do not award this mark if:more than one final burette reading is 50.(00)50(.00) is used as an initial burette reading any burette reading is greater than 50.(00) IV There are two uncorrected accurate titres within 0.10 cm3Do not include a reading if it is labelled rough.Do not award this mark if, having performed two titres within 0.10 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 0.10 cm3 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. two (or more) accurate identical titres (ignoring rough), then two (or more) accurate titres within 0.05 cm3, then two (or more) accurate titres within 0.10 cm3 etc. Examiner rounds any burette readings to the nearest 0.05 cm3 and then selects the best titres using the hierarchy:These best titres are used to calculate the mean corrected titre to the nearest 0.01 cm3. Award V, VI and VII if0.20 (cm3) Award V and VI if 0.20 <0.40 Award V, only, if 0.40 <0.80 Spread penalty: if the two best (corrected) titres used by the Examiner were0.50 cm3 apart, cancel one Q mark. 1 1 1Cambridge International Examinations 2014 [7]<br />
Page 3 Mark Scheme Syllabus Paper Cambridge International AS/A LevelOctober/November 2014 9701 34 Question Indicative material Mark Total (b)Candidate averages two (or more) titres where the total spread is 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, and be correctly rounded to nearest 0.01 cm3. Two special cases, where the mean need not be to 2 dp:Allow mean to 3 dp only for 0.025 or 0.075 (e.g. 26.325 cm3)Allow mean to 1 dp, if all accurate burette readings were given to 1 dp and the mean is exactly correct. Note: the candidates mean will sometimes be marked correct even if it was different from the mean calculated by the Examiner for the purpose of assessing accuracy. (c) (i) Number of moles of KMnO4 used = 0.0250(b) 1000 (ii) 2KMnO4 + 5H2O2 + 3H2SO4K2SO4 + 2MnSO4 + 8H2O + 5O2 (iii) + (iv) (iii) number of moles of H2O2 (in 10 cm3) = 2.5(i) (iv) number of moles of H2O2 (in 1.0 dm3) = 100(iii) Allow ecf in (iii) to incorrect equation (v) Concentration in FB 3 = (iv)10 (c) Answers to parts (i), (iii), (iv) and (v) given to 3 or 4 sf A minimum of 3 answers is needed to qualify for the mark. All answers given must have appropriate sig figs. Qn 1 [1] [5] Total [13]Cambridge International Examinations 2014<br />](https://learnah.org/wp-content/uploads/2018/08/November_2014_v4_MS_-_Paper_3_CIE_Chemistry_A-level_1-0.jpg)
