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CIE Nov 2016 v1 Paper 3 Q2
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![PMT (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 the volume of FA 3 you calculated in (b). (ii) Use your answer to (i) and the equation on page 4 to determine the number of moles of hydrochloric acid, HCl, present in the 25.0 cm3 of FA 4 pipetted in (a). moles of NaOH =mol (iii) Use your answer to (ii) to calculate the number of moles of hydrochloric acid, HCl, remaining in flask X after the reaction in 1(a). moles of HCl =mol (iv) Use the relevant information on page 2 to calculate the number of moles of hydrochloric acid, HCl, pipetted into flask X in 1(a). moles of HCl remaining =mol moles of HCl pipetted into flask X =mol (v) Use your answers to (iii) and (iv) to calculate the number of moles of hydrochloric acid, HCl, which reacted with the marble chips in flask X. moles of HCl which reacted in flask X =molUCLES 2016 9701/31/O/N/16 [Turn over<br />
(vi) Use your answer to (v), the equation in Question 1 and the Periodic Table on page 12 to calculate the mass of pure calcium carbonate, CaCO3, in the sample of industrial grade calcium carbonate, FA 1. PMT (vii) Use your answer to (vi) and the mass of marble chips recorded in 1(a) to calculate the percentage purity of FA 1. mass of CaCO3 =g percentage purity of FA 1 =% [5] (d) You have carried out two different methods to find the percentage purity of industrial grade calcium carbonate. A source of error in Question 1 is that some carbon dioxide escapes before the bung can be inserted. How would this affect the percentage purity of FA 1 calculated in the two questions? Explain your answers. Question 1Question 2[3] [Total: 16]UCLES 2016 9701/31/O/N/16<br />](https://learnah.org/wp-content/uploads/2018/08/November_2016_v1_QP_-_Paper_3_CIE_Chemistry_A-level_2-0.jpg)
![PMT Question 2(a) Page 3 Cambridge International AS/A LevelOctober/November 2016 Mark Scheme Syllabus 9701 Paper 31 Answer Marks I Initial and final burette readings and volume added recorded for rough titre and accurate titre details tabulated. [minimum 22 boxes with relevant information] II Initial and final burette readings recorded and volume of FA 3 added recorded for each accurate titration. Headings and units correct for accurate titrations Headings: initial / final (burette) reading / volume or reading / volume at start / finish and volume / FA 3 added / used or titre [not difference/total] allow vol but not V and Units: (cm3) or / cm3 or in cm3 [or cm3 by every entry] III All accurate burette readings are recorded to the 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(.0) IV Final uncorrected titre is within 0.10 cm3 of any previous uncorrected accurate titre. Do not include a reading if it is labelled rough. Do not award the mark if any accurate burette readings (apart from the initial zero) are given as integers.UCLES 2016<br />
Question Page 4 Cambridge International AS/A LevelOctober/November 2016 Mark Scheme Syllabus 9701 Paper 31 Answer Marks V, VI and VII 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 uses the best titre to calculate the ratio of acid remaining after reaction with calcium carbonate in Question 1 to this best titre from Question 2 for Supervisor and each candidate. The ratio of this value for the candidate is compared to the ratio of this value for the Supervisor and marks awarded as follows. Award V, VI and VII for 0.951.05 Award V and VI for 0.901.10 Award V for 0.801.20 PMTUCLES 2016<br />
Question 2(b) 2(c)(i) and (ii) 2(c)(iii) and 2(c)(iv) 2(c)(v) 2(c)(vi) Page 5 Cambridge International AS/A LevelOctober/November 2016 Mark Scheme Syllabus 9701 Paper 31Candidate must average two (or more) titres where the total spread is0.20 cm3. Check mean titre is correctly calculated from clearly selected values (ticks or working). Answer The mean should normally be quoted to 2 dp rounded to the nearest 0.01.Working must be shown or ticks must be put next to the two (or more) accurate readings selected.[e.g. 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 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: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. the rough titre was used to calculate the mean; 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 calculation of mean) are integers. 0.140 (1000 Correctly calculates and same answer in (ii) and both answers to 3 or 4 sf Correctly uses (ii)10 and Answer = 5.(00)102 Correctly calculates (iv)(iii) Correctly uses [(v)100.1]/2UCLES 2016 PMT Marks<br />
Page 6 Cambridge International AS/A LevelOctober/November 2016 Mark Scheme Syllabus 9701 Paper 31 PMT Correctly uses [(vi)100)/(mass in (a)] to a minimum of 2 sf Answer Question 1: % purity lower as loss of gas means fewer moles / less mass CaCO3 Question 2: no change / % same as same amount of acid reacts / (amount) acid left is same Answer FA 5 is NaNO3(s); FA 6 is CuCO3(s); FA 7 is NaBr(aq) FA 5 FA 6 (goes to) colourless or yellow liquid/ solution gas relights glowing splint (green) powder / solid (turns) black / black residue or gas turns limewater milky / cloudy white / chalky / forms white ppt gas (turns) brown / brown gas or solution turns blue (pale) blue solution / liquid formedUCLES 2016 1 1 1 1 Marks 4 max 3 16 Total Marks 1+1 1 1+1 Question 2(c)(vii) 2(d) Question 3(a)(i)<br />](https://learnah.org/wp-content/uploads/2018/08/November_2016_v1_MS_-_Paper_3_CIE_Chemistry_A-level_2-0.jpg)
