CIE Nov 2017 v3 Paper 3 Q2

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(d) (i) Calculate the maximum percentage error in one of your accurate titres. PMT (ii) A student suggests that the experiment could be made more accurate if the volume of FA 3 was measured using a burette. maximum percentage error =% Give a reason why the student might make this suggestion.Explain why this change would not improve the accuracy of the experiment.[3] [Total: 16]UCLES 2017 9701/33/O/N/17<br /> PMT Question 2 starts on the next page.UCLES 2017 9701/33/O/N/17 [Turn over<br /> PMT In this experiment you will determine the value of y in the formula for hydrated barium chloride, BaCl 2.yH2O. You will do this by measuring the mass loss when a sample of hydrated barium chloride is heated. BaCl 2.yH2O(s) BaCl 2(s) + yH2O(g) FA 5 is hydrated barium chloride, BaCl 2.yH2O. (a) Method Before starting any practical work, read through all the instructions and prepare a table for your results in the space provided.Weigh the crucible with a lid and record the mass. Add all the FA 5 to the crucible. Reweigh the crucible with the lid and FA 5. Record the mass. Place the crucible in the pipe-clay triangle on top of a tripod. Heat the crucible gently with the lid on for about 1 minute. Remove the lid and then heat more strongly for a further 4 minutes. Replace the lid and allow the crucible to cool. While the crucible is cooling you may wish to begin work on Question 3. Once the crucible has cooled, reweigh the crucible with the lid and contents. Record the mass. Calculate and record the mass of FA 5 used, the mass of the residue and the mass of water lost. II III IV [5]UCLES 2017 9701/33/O/N/17<br /> PMT (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 barium chloride in the residue. You may assume all the water has been removed. (ii) Calculate the number of moles of water lost. moles of BaCl 2 =mol (iii) Calculate the value of y in BaCl 2.yH2O. moles of H2O lost =mol y =[3] (c) (i) For this experiment to give an accurate value for y, anhydrous barium chloride must be thermally stable. Explain fully what would happen to the value of y if BaCl 2 were to decompose slightly during heating.(ii) Starting with the same mass of hydrated barium chloride, suggest how you could modify the experiment to determine more accurately the mass of water lost.[3]UCLES 2017 9701/33/O/N/17 [Total: 11] [Turn over<br />

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