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CIE Nov 2013 v6 Paper 3 Q2
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![Examiners For Use In this experiment you will heat two separate samples of a hydrated salt to drive off the water of crystallisation. You will then calculate the relative atomic mass of the metal in the salt. FB 6 is the hydrated salt. The formula of FB 6 is MSO4.7H2O, where M is the metal. (a) Method Record all weighings, in an appropriate form, in the space below.Record the mass of the empty crucible without its lid. Add between 2.0 and 2.4 g of FB 6 into the crucible. Record the mass of the crucible and its contents. Use a pipe-clay triangle to support the crucible and contents on a tripod. Heat the crucible and its contents gently and carefully for about two minutes, with the lid off. Then heat very strongly for a further three minutes. Put the lid on the crucible and leave it to cool for approximately 10 minutes. While you are waiting for the crucible to cool, start work on Question 3.When the crucible is cool, remove the lid, and weigh the crucible with the residue. Record the mass of anhydrous MSO4 remaining in the crucible after heating and therefore calculate the mass of water lost. To prepare for the second experiment, use a spatula to remove the solid residue from the crucible into the beaker labelled waste. Reweigh the empty crucible without its lid. Carry out the experiment again. This time use between 2.5 and 2.9 g of FB 6. II III IV VI [6]UCLES 2013 9701/36/O/N/13 [Turn over<br />
Examiners For Use (b) Calculation Show your working and give your answers to three signi cantgures. (i) State and explain which of your two experiments in (a) is likely to be the more accurate.(ii) Calculate the number of moles of water removed from the hydrated salt in the more accurate experiment. (Ar : H, 1.0; O, 16.0) moles of H2O =mol (iii) Complete the equation for the removal of water from hydrated FB 6. Include state symbols. MSO4.7H2O ()() + () (iv) Using your answer to (ii), calculate the number of moles of anhydrous MSO4 produced in the more accurate experiment. (v) Use the mass of anhydrous MSO4 produced in the more accurate experiment to calculate the relative formula mass of MSO4. moles of MSO4 =mol relative formula mass of MSO4 =UCLES 2013 9701/36/O/N/13<br />
Examiners For Use (vi) Calculate the relative atomic mass of M. (Ar : O, 16.0; S, 32.1) (If you were unable to calculate the relative formula mass of anhydrous MSO4 you may assume that it was 126.3. This is not the correct value.) Ar of M =(vii) The relative atomic masses of some of the cations on page 11 are given below. (Ar : Mg, 24.3; Ca, 40.0; Fe, 55.8; Cu, 63.5; Mn, 54.9; Zn, 65.4) M is a cation of one of the elements listed above. Suggest the identity of M and justify your answer.(viii) Suggest why it was not necessary to include the cations aluminium and chromium from page 11 in the list of relative atomic masses in (vii).[8] (c) The crucible was cooled with the lid on to prevent absorption of water vapour from the air. Suggest a better way of preventing water vapour being absorbed during cooling.[1] [Total: 15]UCLES 2013 9701/36/O/N/13 [Turn over<br />](https://learnah.org/wp-content/uploads/2018/08/November_2013_v6_QP_-_Paper_3_CIE_Chemistry_A-level_2-0.jpg)
![Page 4 Mark Scheme Syllabus Paper GCE A LEVELOctober/November 2013 9701 36 PMT 1 (d) ACE error = 0.05 cm in (i) interpretation and 2 (a) [1] % error in volume of FB 5 =100 in vol of 5FB used 0.05 (ii) MMO collection I The masses of FB 6 used by the candidate were between 2.02.4 g (expt 1) and 2.52.9 g (expt 2). PDO II Suitable headings for a table or list, shown completely display for at least one experiment. If 2 experiments, all headings must be correct.(mass of) empty crucible(mass of) crucible + FB 6(mass of) crucible + residue/FB 6 after heatingmass (water) lost or mass anhydrous remaining and unit covering every weighing. Unit/g or (g) or in grams or g following each weighing. PDO recording MMO quality III Records all balance readings consistently to at least 1 dp A minimum of three weighings are needed. of mass hydrated salt Examiner calculates for each of mass water experiment. Award IV if the ratio in expt 1 is between 0.95 and 1.15. Award V If the ratio in expt 2 is between 0.95 and 1.15. Award VI If the ratio in both of experiments 1 and 2 is between 0.85 and 1.25. [Total: 14] [6] 2 (b) MMO (i) An appropriate choice of the more accurate quality experiment, and justification of choice. Three possibilities:Experiment 2 uses a larger mass and has a greater percentage accuracy.A reference to either experiment spitting or frothing during heating is a valid reason for nominating the other experiment. heating.Experiment 1 as smaller mass takes less ACE (ii) Correctly calculates number of moles of water interpretation = mass of water lost 18 Candidate must use the mass loss for the Ans to 24 sf choice is expressed in (i), this should be expt 2.) Allow (l) for water. experiment thought to be more accurate. (If no ACE (iii) MSO4.7H2O(s) MSO4(s) + 7H2O(g) conclusionCambridge International Examinations 2013<br />
Page 5 Mark Scheme Syllabus Paper GCE A LEVELOctober/November 2013 9701 36 PMT ACE (iv) Correct answer calculated interpretation n(MSO4) = n(water) i.e. answer (ii) divided by 7 Ans to 24 sf ACE (v) Method mark showing the numbers for the interpretation expression Relative formula mass = mass of residue no of moles Mass of residue from same expt as mass of water Ans to 24 sf ACE (vi) Correct answer calculated interpretation Ar = Mr96.1 . Candidates are allowed to use 126.3 as the Mr. In this case, the Ar = 30.2. Ans 24 sf Penalise sf once only within (b) ACE (vii) Correct identification of M as magnesium conclusion and explanation that this Ar is closest to value calculated. Allow alternative identity of metal as ecf from Ar value. ACE (viii) (M is divalent but) Al and Cr are both trivalent conclusion or (M forms 2+ ion whereas) Al and Cr are 3+ or sulfates of Cr/Al are not CrSO4 and AlSO4 (ora) ref to both needed 2 (c) ACE Cool in a desiccator Improvement or cool in closed container with a (named) drying agent [8] [1] [Total: 15]Cambridge International Examinations 2013<br />](https://learnah.org/wp-content/uploads/2018/08/November_2013_v6_MS_-_Paper_3_CIE_Chemistry_A-level_2-0.jpg)
