CIE Jun 2013 v2 Paper 5 Q2

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Hydrated copper(II) sulfate can be represented as CuSO4.xH2O where x is the number of molecules of H2O for each CuSO4. When the compound is heated, it loses the molecules of water leaving anhydrous copper(II) sulfate. Examiners For Use A suggested equation is: CuSO4.xH2O(s)CuSO4(s) + xH2O(g) An experiment is carried out to attempt to determine the value of x.An open crucible is weighed and the mass recorded. A sample of hydrated copper(II) sulfate is added to the crucible and the new mass recorded. The crucible with hydrated copper(II) sulfate is heated strongly forve minutes and allowed to cool back to room temperature. The crucible with the contents is then reweighed and the mass recorded.(a) Calculate the relative formula masses, Mr, of CuSO4 and H2O. [Ar: H, 1.0; O, 16.0; S, 32.1; Cu, 63.5] [1] (b) The results of several of these experiments are recorded below. Process the results in the table to calculate both the number of moles of anhydrous copper(II) sulfate and the number of moles of water. Record these values in the additional columns of the table. You may use some or all of the columns. Masses should be recorded to two decimal places, while the numbers of moles should be recorded to three signi cantgures. Label the columns you use. For each column you use include units where appropriate and an expression to show how your values are calculated. You may use the column headings A to G for these expressions (e.g. AB). mass of crucible / g 15.20 15.10 14.95 15.15 15.05 14.90 14.92 15.30 15.07 15.01 mass of crucible + CuSO4.xH2O / g mass of crucible + CuSO4 / g 16.76 16.90 16.95 17.25 17.32 17.24 17.42 17.99 17.96 18.09 16.20 16.25 16.23 16.49 16.47 16.43 16.52 17.02 16.92 16.98UCLES 2013 9701/52/M/J/13 [2]<br /> (c) Plot a graph to show the relationship between the number of moles of anhydrous copper(II) sulfate, CuSO4 (x-axis), and the number of moles of water (y-axis). Draw the line of bestt. It is recommended that you do not include the origin in your choice of scaling.UCLES 2013 9701/52/M/J/13 [3] [Turn over<br /> Examiners For Use 10 (d) Circle and label on the graph any point(s) you consider to be anomalous. For each anomalous point give a different reason why it is anomalous clearly indicating which point you are describing.[3] (e) Determine the slope of the graph. You must mark clearly on the graph any construction lines and show clearly in your calculation how the intercepts were used in the calculation of the slope. [3] (f) Comment on the reliability of the data provided in (b).[1] (g) (i) Use the value of the slope of your graph calculated in (e) to suggest the correct formula for hydrated copper(II) sulfate.(ii) Explain your answer to (i).[2] [Total: 15]UCLES 2013 9701/52/M/J/13<br />

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