CIE Jun 2014 v5 Paper 3 Q2

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You are to determine the percentage by mass of zinc carbonate in a sample of powdered zinc carbonate ore by means of thermal decomposition. You may assume that none of the other components of the ore is affected by heating. The equation for the reaction occurring is given below. ZnCO3(s)ZnO(s) + CO2(g) PMT FA 4 is zinc carbonate ore. (a) Method Read through the method before starting any practical work and prepare a table for your results in the space below.Weigh the empty crucible and record the mass in your table. Transfer all the FA 4 into the crucible. Weigh the crucible with FA 4 and record the mass. Place the crucible on the pipe-clay triangle. Heat the crucible gently for about one minute and then strongly for four minutes. Remove the Bunsen burner and allow the crucible to cool. While the crucible is cooling start working on another question. Reweigh the cooled crucible with contents and record the mass. Record the mass of FA 4 used and the mass of solid remaining after heating. Beneath your table, record any observations you have made while the solid was heated and cooled. II III IV [4]UCLES 2014 9701/35/M/J/14<br /> (b) Calculations Show your working and appropriate signi cantgures in thenal answer to each step of your calculations. (i) From your results in (a), calculate the mass of carbon dioxide lost on heating FA 4. PMT (ii) Use your answer to (i) to calculate the mass of zinc carbonate present in the sample of FA 4 that was heated. [Ar: C, 12.0; O, 16.0; Zn, 65.4] mass of CO2 lost =g (iii) Calculate the percentage by mass of zinc carbonate in the zinc carbonate ore. mass of ZnCO3 =g percentage of ZnCO3 =% [4] (c) Suggest how a student, using all the same apparatus, could alter the method to be more con dent that the percentage of zinc carbonate is correct. Explain your answer.[2] [Total: 10] II III IVUCLES 2014 9701/35/M/J/14 [Turn over<br />

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