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CIE Jun 2016 v1 Paper 3 Q1
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![In this experiment you will determine the identity of the Group 2 metal, X, in the carbonate, XCO3. To do this you will react a known mass of XCO3 with excess hydrochloric acid, HCl, and measure the mass of carbon dioxide that is given off. PMT FA 1 is XCO3. FA 2 is hydrochloric acid, HCl. (a) MethodWeigh the stoppered tube containing FA 1 and record its mass. Use the measuring cylinder to transfer 25 cm3 of FA 2 into the 250 cm3 beaker. Weigh the beaker containing the acid and record the mass. Carefully add all the sample of FA 1 to the acid in the beaker. Stir the mixture until there is no further reaction. Reweigh the beaker and its contents and record the mass. KEEP THE CONTENTS OF THE BEAKER FOR USE IN QUESTION 2. Reweigh the stoppered tube containing any residual FA 1 and record its mass. Calculate the mass of FA 1 added to the acid and record this value. Calculate the mass of carbon dioxide given off and record this value. II III IV VI VII [7] (b) 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 carbon dioxide given off when XCO3 reacted with the acid. Use the data in the Periodic Table on page 16. (ii) Write the equation for the reaction of FA 1, XCO3, with hydrochloric acid, HCl. Include state symbols.moles of CO2 =molUCLES 2016 9701/31/M/J/16<br />
(iii) Use your answers to (i) and (ii) to calculate the number of moles of XCO3 that were added to the acid. PMT (iv) Use your answer to (iii) to calculate the relative atomic mass, Ar, of X. Identify X. moles of XCO3 =mol II III IV Ar of X =X is. [5] (c) One of the sources of error in this experiment is that it is very difficult to reduce acid spraying out of the beaker when the metal carbonate is added to the acid. (i) Explain what effect this acid spray would have on the value you calculated for the relative atomic mass, Ar, of X.(ii) Why is a small amount of acid spray not likely to cause an error in the identification of X?(iii) How could you minimise acid spraying out of the beaker?[3]UCLES 2016 9701/31/M/J/16 [Total: 15] [Turn over<br />](https://learnah.org/wp-content/uploads/2018/08/June_2016_v1_QP_-_Paper_3_CIE_Chemistry_A-level_1-0.jpg)
![Page 2 Question Cambridge International AS/A LevelMay/June 2016 9701 31 Mark Scheme Syllabus Paper Indicative material Mark Total [7] [5] (a) I Six identifiable masses recorded II All recorded masses have unambiguous headings and unit: / g or (g) or g (for each heading) by each entry. III Four measured masses all recorded to the same number of decimal places minimum 1 decimal place IV Correctly calculates mass of FA1 added and mass of CO2 evolved. V, VI and VII Examiner compares corrected mass of FA1 / corrected mass of CO2 with supervisor value. Accuracy marks are awarded as shown. Award V, VI and VII if0.10 Award V and VI if 0.10 <0.20 Award V if 0.20 <0.40 (b) (i) I Correctly calculates n(CO2) (mass CO2 / 44) (ii) (iii) (iv) (iv) (c) (i) (ii) II Correct equation and all state symbols XCO3(s) + 2HCl(aq)XCl 2(aq) + H2O(I) + CO2(g) III (iii) = (i) and Expression mass of FA1 / (iii) shown in (iv) IV Correctly uses 60 and the Mr to calculate Ar of X (mass of FA1 / (iii)60) Identifies X as Group 2 metal or ion with nearest Ar value (must have some working for Ar used). Be 9.0, Mg 24.3, Ca 40.1, Sr 87.6, Ba 137.3 Apparently more moles of CO2 (lost) so Ar of X is smaller. or Apparently more moles of XCO3 (used) so Ar of X is smaller. Any 2 from:Small loss in massnot much difference to Ar so does not cause confusion in identity / still closest to identity of XCambridge International Examinations 2016<br />
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 />](https://learnah.org/wp-content/uploads/2018/08/June_2016_v1_MS_-_Paper_3_CIE_Chemistry_A-level_1-0.jpg)
