The following table lists the solubilities of the hydroxides and carbonates of some of the Group 2 elements, M, at 25 °C. solubility/mol dm⁻³ element M M(OH)₂ MCO₃ Mg 2.0 × 10⁻⁴ 1.5 x 10⁻³ Ca 1.5 x 10⁻² 1.3 x 10⁻⁴ Sr 3.4 x 10⁻² 7.4 x 10⁻⁵ Ba 1.5 x 10⁻¹ 9.1 x 10⁻⁵

1. (a)(i)Explain why the solubility of the Group 2 hydroxides, M(OH)₂, increases down the group.[3]
2. (a)(ii)Suggest a reason for the general decrease in the solubility of the Group 2 carbonates, MCO₃, down the group.[1]
3. (a)(iii)When carbon dioxide is passed through a saturated solution of calcium hydroxide (limewater), a white precipitate of calcium carbonate is formed. Use the data in the table to deduce, for each of Mg, Sr and Ba, whether or not a saturated solution of its hydroxide could also be used to test for carbon dioxide. Explain your answer. No calculations are required.[2]
4. (b)(i)Calculate the value of the solubility product, Ksp, of magnesium hydroxide at 25°C. Ksp =[2]
5. (b)(ii)State what would be observed if a few drops of a saturated solution of barium hydroxide are added to a saturated solution of barium carbonate. Explain your answer. observation explanation[2]
6. (c)The equation for the formation of the gaseous hydroxide ion is shown. ½H₂(g) + ½O₂(g) + e⁻ → OH⁻(g) ΔH = ΔHᶠ(OH⁻(g)) Use data in the table and from the Data Booklet to calculate ∆Hᶠ(OH⁻(g)). You might find it useful to construct a Born-Haber cycle. enthalpy change ∆Hᶠ/kJ mol⁻¹ atomisation of Mg(s) +148 formation of Mg(OH)₂(s) -925 lattice energy of Mg(OH)₂(s) -2993 ΔHᶠ(OH⁻(g)) = kJ mol⁻¹[3]