CIE Jun 2017 v2 Paper 4 Q5

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(a) 1,2-diaminoethane, en, H2NCH2CH2NH2, is a bidentate ligand. 12 PMT (i) What is meant by the terms bidentate and ligand? bidentateligand[2] (ii) There are three isomeric complex ions with the formula [Cr(en)2Cl 2]+. Complete the three-dimensional diagrams of the isomers in the boxes. You may use N N to represent en. Cr Cr Cr (b) Copper forms complexes with NH3 and en according to equlibria 1 and 2. equilibrium 1 Cu2+(aq) + 4NH3(aq) [Cu(NH3)4]2+(aq) equilibrium 2 Cu2+(aq) + 2en(aq) [Cu(en)2]2+(aq) (i) Write the expressions for the stability constants, Kstab1 and Kstab2, for equilibria 1 and 2. Include units in your answers. [3] Kstab1 = Kstab2 = units =units =[3]UCLES 2017 9701/42/M/J/17<br /> PMT 13 (ii) An equilibrium is set up when both en and NH3 ligands are added to a solution containing Cu2+(aq) as shown in equilibrium 3. equilibrium 3 [Cu(NH3)4]2+(aq) + 2en(aq) [Cu(en)2]2+(aq) + 4NH3(aq) Write an expression for the equilibrium constant, Keq3, in terms of Kstab1 and Kstab2. Keq3 =[1] (iii) The numerical values for these stability constants are shown. Kstab1 = 1.21013 Kstab2 = 5.31019 Calculate the value of Keq3 stating its units. Keq3 =unit =[2] (c) S o values for equilibria 1 and 2 differ greatly, as can be seen in the table. All values are at a temperature of 298 K. equilibrium H o / kJ mol1 S o / J K1 mol1 G o / kJ mol1 1 2 92 100 60 +40 74 (i) Explain why is so different from[1] (ii) Calculate at 298 K. =kJ mol1 [2] (iii) What conclusion can be made about the relative feasibility of equilibria 1 and 2? Explain your answer.[1] (iv) Using data from the table, suggest a value of H o for equilibrium 3.[1] (v) State the type of reaction that is occurring in equilibrium 2.[1]UCLES 2017 9701/42/M/J/17 [Total: 17] [Turn over<br />

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