CIE Nov 2017 v1 Paper 3 Q2

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Zinc carbonate occurs in a basic form, which means that zinc hydroxide is also present. The chemical formula of basic zinc carbonate can be written as ZnCO3.yZn(OH)2, where y may not be an integer. In this experiment you will heat basic zinc carbonate to decompose it and use your results to determine the value of y. PMT When basic zinc carbonate is heated, it decomposes as shown. ZnCO3.yZn(OH)2(s) (1 + y)ZnO(s) + CO2(g) + yH2O(g) FA 5 is basic zinc carbonate, ZnCO3.yZn(OH)2. (a) Method Read through the method before starting any practical work. Prepare a table for all your results from Experiments 1 and 2 in the space on page 5. Experiment 1Weigh a crucible with its lid and record the mass. Add 2.12.5 g of FA 5 to the crucible. Weigh the crucible and lid with FA 5 and record the mass. Place the crucible in the pipe-clay triangle on top of the tripod. Heat the crucible and contents gently for 1 minute with the lid on. Remove the lid. Heat the crucible and contents strongly, with the lid off, for approximately 4 minutes. Replace the lid and leave the crucible and residue to cool for at least 5 minutes, before re-weighing it with the lid on. Record the mass. While the crucible is cooling, you may wish to begin work on Question 3. Calculate, and record in your table, the mass of FA 5 used and the mass of residue obtained. (i) State the observation(s) you made while you were heating FA 5.(ii) State the observation(s) you made once the residue had cooled down.Experiment 2Repeat the procedure used in Experiment 1, using 1.51.9 g of FA 5 and using the other crucible and lid. Record the three balance readings made during the experiment. Calculate and record the mass of FA 5 used and the mass of residue obtained.UCLES 2017 9701/31/O/N/17<br /> Results PMT II III IV VI [6] (b) Calculations Show your working and appropriate significant figures in the final answer to each step of your calculations. (i) Calculate the relative formula mass, Mr, of zinc hydroxide, Zn(OH)2. (ii) Using your answer to (i), write down an expression, in terms of y, for the relative formula mass, Mr, of basic zinc carbonate, ZnCO3.yZn(OH)2. Mr of Zn(OH)2 =Mr of ZnCO3.yZn(OH)2 =(iii) Using the mass of ZnCO3.yZn(OH)2 from Experiment 1 and your answer to (ii), write down an expression, in terms of y, for the number of moles of ZnCO3.yZn(OH)2 that you heated in Experiment 1. moles of ZnCO3.yZn(OH)2 =molUCLES 2017 9701/31/O/N/17 [Turn over<br /> (iv) Using your answer to (iii) and the equation below, write an expression, in terms of y, for the number of moles of zinc oxide produced in Experiment 1. ZnCO3.yZn(OH)2(s) (1 + y)ZnO(s) + CO2(g) + yH2O(g) PMT moles of ZnO produced =mol (v) Use your results from Experiment 1 to calculate the number of moles of zinc oxide, ZnO, obtained in the residue. You may assume complete decomposition has occurred. (vi) Using your answers to (iv) and (v), calculate the value of y to one decimal place. moles of ZnO =mol y =[6] (c) (i) Apart from altering the balance or the masses of FA 5 used, state one improvement you could make to the experimental procedure to improve its accuracy.(ii) Which experiment should be more accurate, Experiment 1 or Experiment 2? Explain your answer.[2] [Total: 14]UCLES 2017 9701/31/O/N/17<br />

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