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48 T HE P ERIODIC TABLE (5) Example Ba(s) + 2H2O(l) Ba(OH)2(aq) + H2(g) The metal hydroxide is often produced as a suspension in water. Solubility of group 2 hydroxides and sulphates Solubility data for group 2 hydroxides in water at 298 K are given below. 4 × 10–3 Ba(OH)2 15 × 10–3 As the group is descended, the solubility of the group 2 hydroxides increases. Mg(OH)2 is insoluble, both Ca(OH)2 and Sr(OH)2 are slightly soluble and Ba(OH)2 is fairly soluble. Solubility data for group 2 sulphates in water at 298 K are given below.
Cl 120° B Cl Cl Four bond pairs, CH4 The electron pairs adopt a tetrahedral arrangement. 5° 35 S TRUCTURE AND B ONDING (10) Five bond pairs, PCl5 The electron pairs are arranged in a trigonal bipyramidal shape. Cl Cl 120° P Cl Six bond pairs, SF6 The electron pairs are arranged in an octahedral shape. 90° Cl Cl F F F 90° S F F F Species with lone pairs Examples Four electron pairs as three bond pairs and one lone pair, NH3 or PCl3 H Four electron pairs as two bond pairs and two lone pairs, H2O The shape is V-shaped (bent).
1) (b) Sodium bromide. (1) (c) Lithium iodide. (1) 4 Explain briefly the origin of the colours in flame tests. (2) 5 (a) Write an equation, including state symbols, for the reaction between calcium and water. (2) (b) State the trend in solubility of the hydroxides of the group 2 elements as the atomic mass of the metal increases. (1) 6 Compare the reaction when sodium is burned in a plentiful supply of oxygen with that of magnesium and oxygen. Account briefly for any differences. (4) 7 When a sample of magnesium nitrate is heated, it gives off a brown gas and a gas that relights a glowing splint.