CIE Nov 2016 v6 Paper 3 Q2 (with explained solutions) |

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CIE Nov 2016 v6 Paper 3 Q2

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Solid hydrated copper(II) sulfate has the formula CuSO4.xH2O where x is the number of moles of water of crystallisation present in 1 mole of compound. PMT You will determine the equation for the reaction that occurs when hydrated copper(II) sulfate is heated to remove the water of crystallisation producing anhydrous copper(II) sulfate. FB 3 is hydrated copper(II) sulfate CuSO4.xH2O. (a) Method Record all masses in the space below.Weigh the crucible and add 2.22.4 g of FB 3. Weigh the crucible plus FB 3. Place the crucible on the pipe-clay triangle and heat it gently for approximately 4 minutes. Leave the crucible to cool and reweigh the crucible plus residue. Keep the crucible and residue for test (c). II III IV [4] (b) Calculations Show your working and appropriate significant figures in the final answer to each step of your calculations. (i) Calculate the mass of anhydrous copper(II) sulfate, CuSO4, produced after heating. (ii) Calculate the mass of water lost by heating. mass of CuSO4 =g mass of water =gUCLES 2016 9701/36/O/N/16 [Turn over<br />
(iii) Use your answers to (i) and (ii) and the Periodic Table on page 12 to deduce the value of x in the formula CuSO4.xH2O. PMT (iv) Use your answer to (iii) to complete the equation for the reaction that occurs when hydrated copper(II) sulfate is heated. You should include state symbols. CuSO4H2O()CuSO4() + H2O() [4] x is(c) Place the cooled crucible, with the residue, on a heatproof mat and carefully add a few drops of water. (i) Note your observations.(ii) Explain your observations in (i) in terms of the reaction occurring.[3] (d) Two students carried out the experiment in (a) and obtained values for x that did not agree with the accepted value. One student calculated a value that was less than the accepted value and the other student calculated a value that was more than the accepted value. In each case, suggest a reason for the error and an improvement that could be made to minimise it. You can assume that the calculations were correctly carried out. Value less than accepted value errorimprovementValue more than accepted value errorimprovement[2] [Total: 13]UCLES 2016 9701/36/O/N/16<br />

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Page 5 Cambridge International AS/A LevelOctober/November 2016 Mark Scheme Syllabus 9701 Paper 36 Answer Marks Question 2(a) 2(b)(i) and (ii) 2(b)(iii) Mass of solid used between 2.20 and 2.40 g Table with correct headings / unitsmass of cruciblemass of crucible + FB 3mass of crucible + residue / FB 3 after heating Award III if % mass loss is30 but42 Award III and IV if % mass loss is33 but39 Units: / g, (g), in g, in gram(me)s Correctly calculates mass of anhydrous salt AND mass of water lost. Shows expression: mass water mass anhydrous Correctly calculates, including showing working, value of x from (iii) and gives as integer 159.6 18 2(b)(iv) Equation completed with x from (iii) and state symbols 2(c)(i) (Solid) turns blue and steam / water vapour given off / temperature rises / heat released / hissing / sizzling (owtte) 2(c)(ii) Anhydrous salt returns to hydrated or original formula quoted Reaction is exothermicUCLES 2016 1 1 1 1 1 1<br />
Page 6 Cambridge International AS/A LevelOctober/November 2016 Mark Scheme Syllabus 9701 Paper 36 Question 2(d) Answer Marks Value less than accepted value: not all water removed and heat to constant mass Value more than accepted value: (anhydrous) salt decomposes and practical method of limiting temperature / heat very gently / thermostatically controlled oven 1 1 Total: 13UCLES 2016<br />

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