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CIE Nov 2016 v3 Paper 3 Q1
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![Hydrogen peroxide, H2O2, can be oxidised to give oxygen, O2. This reaction happens rapidly in the presence of acidified potassium manganate(VII), KMnO4. PMT 2MnO4 (aq) + 5H2O2(aq) + 6H+(aq)2Mn2+(aq) + 5O2(g) + 8H2O(l) You will determine the concentration of a solution of hydrogen peroxide. You will first dilute the solution and then carry out a titration using acidified potassium manganate(VII), KMnO4. FA 1 is aqueous hydrogen peroxide, H2O2. FA 2 is 0.0200 mol dm3 potassium manganate(VII), KMnO4. FA 3 is 1.0 mol dm3 sulfuric acid, H2SO4. (a) Method DilutionPipette 25.0 cm3 of FA 1 into the 250 cm3 volumetric flask. Add distilled water to make 250 cm3 of solution and shake the flask thoroughly. Label this diluted solution of hydrogen peroxide FA 4. TitrationFill the burette with FA 2. Rinse the pipette thoroughly with distilled water and then with a little FA 4. Pipette 25.0 cm3 of FA 4 into a conical flask. Use the measuring cylinder to add 25 cm3 of FA 3 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 FA 2 added in each accurate titration. Keep FA 3 and FA 4 for use in Question 2. II III IV VI VII [7]UCLES 2016 9701/33/O/N/16<br />
(b) From your accurate titration results, obtain a suitable value for the volume of FA 2 to be used in your calculations. Show clearly how you obtained this value. PMT 25.0 cm3 of FA 4 requiredcm3 of FA 2. [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 potassium manganate(VII) present in the volume of FA 2 calculated in (b). (ii) Use your answer to (i) and the equation at the top of page 2 to calculate the number of moles of hydrogen peroxide present in 25.0 cm3 of FA 4. moles of KMnO4 =mol (iii) Calculate the concentration, in mol dm3, of H2O2 in FA 4. moles of H2O2 =mol (iv) Calculate the concentration, in mol dm3, of H2O2 in FA 1. concentration of H2O2 in FA 4 =mol dm3 concentration of H2O2 in FA 1 =mol dm3 [4]UCLES 2016 9701/33/O/N/16 [Total: 12] [Turn over<br />](https://learnah.org/wp-content/uploads/2018/08/November_2016_v3_QP_-_Paper_3_CIE_Chemistry_A-level_1-0.jpg)
![PMT Page 2 Cambridge International AS/A LevelOctober/November 2016 Mark Scheme Syllabus 9701 Paper 33 Question 1(a) Answer Marks Initial and final readings and titre value for rough and initial and final reading for two (or more) accurate titrations Appropriate headings and units and the volume of FA 2 added is recorded for each accurate titration. Headings must match readings Initial/start (burette) and reading/volume Final/end (burette) and reading/volume Titre or volume/vol/FA 2 and used/added (not difference, total, V) Units: /cm3 or (cm3) or in cm3 or cm3 for each volume. All accurate burette readings (initial and final) recorded to nearest 0.05 cm3 Do not award this mark if: 50(.00) is used as an initial burette reading; more than one final burette reading is 50.(00); any burette reading is greater than 50.(00) Final uncorrected titre is within 0.10 cm3 of any previous uncorrected accurate titre. Examiner rounds any accurate burette readings to the nearest 0.05 cm3, checks subtractions and then selects the best accurate titres using the hierarchy: identical titres; titres within 0.05 cm3; titres within 0.1 cm3; etc., to calculate mean correct to 0.01 cm3. Examiner compares candidates titre value with that of the Supervisor. 1 1 1 V, VI and VII Award V, VI and VII for0.30 cm3 Award V and VI for 0.30 <0.50 cm3 Award V only for 0.50 <0.80 cm3UCLES 2016<br />
Page 3 Cambridge International AS/A LevelOctober/November 2016 Mark Scheme Syllabus 9701 Paper 33 PMT Answer Marks Question 1(b) Calculation of the mean Check mean titre is correctly calculated from clearly selected values (ticks or working)Candidate must average two (or more) titres where the total spread is0.20 cm3.Working must be shown or ticks must be put next to the two (or more) accurateThe mean should normally be quoted to 2 dp rounded to the nearest 0.01. [e.g. readings selected. 26.667 must be rounded to 26.67.] 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 (ignoring initial given as 0) 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.] Do not award this mark if:the rough titre was used to calculate the mean; the candidate carried out only 1 accurate titration; burette readings were incorrectly subtracted to obtain any of the accurate titre values; all burette readings (resulting in titre values used in the calculation of the mean) are integers. 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) b I Correctly calculates: ( ) 1000 0.0200 1(c)(ii) and 1(c)(iii) 1(c)(iv) II Correctly uses: (i)5/2 and (ii)/0.025 or (ii)1000/25 Correctly calculates: (iii)10 or (ii)1000/25 10UCLES 2016<br />
Answer 3 or 4 significant figures in final answers to all parts (minimum 3 parts attempted) Answer Examiner to calculate 10% and 20% of Supervisors time and round this to nearest second. Candidates time compared with supervisors time. Award 2 marks if time within 10% of supervisor Award 1 mark if time within 20% of supervisor Marks 4 12 Total: Marks Cambridge International AS/A LevelOctober/November 2016 Mark Scheme Syllabus 9701 Paper 33 PMT Page 4 Question Question 2(a) 2(b)(i) Correctly calculates: 2.61105reaction time from (a)UCLES 2016<br />](https://learnah.org/wp-content/uploads/2018/08/November_2016_v3_MS_-_Paper_3_CIE_Chemistry_A-level_1-0.jpg)
