CIE Nov 2017 v2 Paper 4 Q5

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11 (a) The arrangement of the anions around a cation is called the geometry of the cation; e.g. in [CuCl 4]2 the geometry of copper is tetrahedral and the co-ordination number of copper is 4. The geometry of a cation in an ionic compound can be predicted from the ratio of the ionic radii of the cation and anion involved. PMT cation radius anion radius 0.1550.225 0.2250.414 0.4140.732 geometry of cation trigonal planar tetrahedral octahedral Use data from the Data Booklet to predict the geometry of, and hence the co-ordination number of, the cation for sodium chloride, NaCl, geometry of Na+ =co-ordination number of Na+ =magnesium chloride, MgCl 2. geometry of Mg2+ =co-ordination number of Mg2+ =[2] (b) Magnesium(I) chloride, MgCl, is an unstable compound and readily decomposes as shown. 2MgCl (s) Mg(s) + MgCl 2(s) Use the following data to calculate the enthalpy change of this reaction. MgCl (s) = 106 kJ mol1 MgCl 2(s) =642 kJ mol1 enthalpy change =kJ mol1 [1]UCLES 2017 9701/42/O/N/17 [Turn over<br /> PMT 12 (c) (i) The equation for which H is the lattice energy for MgCl is shown. Mg+(g) + Cl (g) MgCl (s) Use the equation, the following data, and relevant data from the Data Booklet to calculate a value for the lattice energy of MgCl. You might find it helpful to construct an energy cycle. electron affinity of Cl (g) = 349 kJ mol1 enthalpy change of atomisation of Mg(s) = +147 kJ mol1 enthalpy change of formation of MgCl (s) = 106 kJ mol1 lattice energy MgCl =kJ mol1 [3] (ii) Suggest how the lattice energies of MgCl 2 and NaCl will compare to that of MgCl. Explain your answers. MgCl 2 and MgClNaCl and MgCl[3] (d) Define the term electron affinity.[2] [Total: 11]UCLES 2017 9701/42/O/N/17<br />

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