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CIE Jun 2014 v3 Paper 3 Q1
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![You are to determine, by titration, the change in oxidation number of a transition metal ion, M2+, when reacted with acidi ed potassium manganate(VII). PMT FA 1 is 0.0200 mol dm3 potassium manganate(VII), KMnO4. FA 2 is 0.0530 mol dm3 transition metal salt, MSO4. FA 3 is 1.0 mol dm3 sulfuric acid, H2SO4. (a) MethodFill the burette with FA 1. Pipette 25.0 cm3 of FA 2 into the conical flask. Use the measuring cylinder to add 25 cm3 of FA 3 into the conical flask. Carry out a rough titration and record your burette readings in the space below. Add FA 1 until the contents of the flask turn a permanent pale pink colour. 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 below, in a suitable form, all of your burette readings and the volume of FA 1 added in each accurate titration. II III IV VI VII [7] (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 2 requiredcm3 of FA 1. [1]UCLES 2014 9701/33/M/J/14<br />
PMT (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 of FA 1 calculated in (b). (ii) Calculate the number of moles of MSO4 in 25.0 cm3 of FA 2. moles of KMnO4 =mol (iii) Use your answers to (i) and (ii) to calculate the number of moles of MSO4 that react with 1 mole of KMnO4. moles of MSO4 in 25.0 cm3 =mol moles of MSO4 =mol (iv) Two possible equations for the reaction of acidi ed KMnO4 with MSO4 are below. equation 1 equation 2 2KMnO4 + 10MSO4 + 8H2SO4K2SO4 + 2MnSO4 + 5M2(SO4)3 + 8H2O 2KMnO4 + 5MSO4 + 8H2SO4K2SO4 + 2MnSO4 + 5M(SO4)2 + 8H2O State and explain which of these two equations is consistent with your answer to (iii).(v) Use your answer to (iv) to state the oxidation number of the transition metal M in the product of the reaction.[5] [Total: 13] II III IVUCLES 2014 9701/33/M/J/14 [Turn over<br />](https://learnah.org/wp-content/uploads/2018/08/June_2014_v3_QP_-_Paper_3_CIE_Chemistry_A-level_1-0.jpg)
![Page 2 Mark Scheme GCE AS/A LEVELMay/June 2014 Syllabus 9701 Paper 33 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) MMO Collection PDO Recording MMO Decisions II Appropriate headings and units for all accurate data. and volume FA 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/FA 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 used by the Examiner 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 33 Mark Total [1] [5] [13] 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) PDO Display 0.0200 (b) I Uses the expression 1000 (or answer correct to 3 or 4 sf) in (i) ACE Interpretation II Correctly evaluates 0.053025 1000 in (ii) (to 3 or 4 sf) III answer to (ii) answer to (i) in (iii) and correct answer to 2, 3 or 4 sf IV Equation 2 as ratio is 5:2 or 2 and reference to their answer in (iii) Allow ecf ACE Conclusion V Oxidation state = (+)4 in (v) from equation 2 Allow ecf ((+)3) Qn 1 TotalCambridge International Examinations 2014<br />](https://learnah.org/wp-content/uploads/2018/08/June_2014_v3_MS_-_Paper_3_CIE_Chemistry_A-level_1-0.jpg)
