(a) Solutions of Group 2 hydrogencarbonates, M(HCO3)2, decompose on heating to give the corresponding metal carbonate, carbon dioxide and water. (i) Write an equation for the decomposition of strontium hydrogencarbonate, Sr(HCO3)2. [1] (ii) The thermal stability of Group 2 carbonates increases down the group. Explain this trend. [2] (b) The hydroxides and fluorides of Group 2 elements show similar trends in solubility. Describe the trend in the solubility of the fluorides of calcium, strontium and barium. Explain your answer. least soluble most soluble explanation [4] (c) (i) Define enthalpy change of hydration, ∆Hhyd [1] (ii) State the main factors that affect the magnitude of enthalpy change of hydration. Explain your answer. [2] (d) Table 1.1 shows various energy changes. Table 1.1 energy change value/kJ mol⁻¹ lattice energy of MgF2 -2957 enthalpy change of hydration, ∆Hhyd, of Mg2+ -1926 enthalpy change of hydration, ∆Hhyd, of F- -505 Use data from Table 1.1 to calculate the enthalpy change of solution, ∆Ηsol, for MgF2(s). It may be helpful to draw a labelled energy cycle. Show your working. ΔΗsol of MgF2(s) = .............................................. kJ mol⁻¹ [2] (e) Mercury(I) fluoride, Hg2F2, is sparingly soluble in water. The cation in Hg2F2 exists as the diatomic ion Hg22+ with a covalent Hg-Hg bond. (i) Write the expression for the solubility product, Ksp, of Hg2F2. Include the units. Ksp = units [2] (ii) The solubility of Hg2F2 is 9.20 × 10⁻³ moldm⁻³ at 298 K. Calculate the value of Ksp of Hg2F2 at 298K. Ksp = [1]