CIE Jun 2016 v2 Paper 4 Q5

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10 Cadmium ions form complexes with primary amines and with 1,2-diaminoethane. Cd2+(aq) + 4CH3NH2(aq) [Cd(CH3NH2)4]2+(aq) Kstab = 3.6106 equilibrium I Cd2+(aq) + 2H2NCH2CH2NH2(aq) [Cd(H2NCH2CH2NH2)2]2+(aq) Kstab = 4.21010 equilibrium II PMT (a) (i) Write an expression for the stability constant, Kstab, for equilibrium I, and state its units. Kstab = units[2] Cadmium ions are poisonous and need to be removed from some water supplies. This is often done by adding a complexing agent. (ii) In a sample of ground water the concentration of Cd2+(aq) is 1.00104 mol dm3. Calculate the concentration of CH3NH2(aq) needed to reduce the concentration of Cd2+(aq) in this dilute solution by a factor of one thousand. concentration of CH3NH2(aq) =mol dm3 [2]UCLES 2016 9701/42/M/J/16<br /> PMT 11 (b) Values for H o and G o for equilibria I and II, and the value of S o for equilibrium I, are given in the table below. All values are at a temperature of 298 K. equilibrium H o / kJ mol1 G o / kJ mol1 S o / J K1 mol1 I II 57.3 56.5 37.4 60.7 66.8 to be calculated (i) Suggest a reason why the H o values for the two equilibria are very similar.[1] (ii) Calculate S o for equilibrium II. S o =J K1 mol1 [1] (iii) Suggest a reason for the difference between the S o you have calculated for equilibrium II and that for equilibrium I given in the table.[1] (iv) Which of the two complexes is the more stable? Give a reason for your answer.[1] [Total: 8]UCLES 2016 9701/42/M/J/16 [Turn over<br />

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