If sodium sulphate is considered to be completely dissociated into cations and anions in aqueous solution, the change in freezing point of water fT , when 0.01 mole of sodium sulphate is dissolved in 1 kg of water, is (kf = 1.86 K Kg mol–1) (2010)

2 2 4 4 2 Na SO Na SO → Vant Hoff factor for 2 4 3 Na SO Hence, 0.01 3 1.86 0.0558 1 f f f T iK m T K x x 136. The elevation in boiling point of a solution of 9.43g of MgCl₂ in 1 kg of water is (Kb = 0.52 K kg mol–1, Molar mass of MgCl₂=94.3g mol–1) (a) 0.156 (b) 0.52 (c) 0.17 (d) 0.94 ? b T 0.52 / b K k mg mole MgCl₂=Mg²⁺ + 2Cl⁻ 1000 b B b B A k W i T M W x x x x Or 9.43 3 0.52 94.3 0.156 b b b T i K m T x x x x 137. What amount of CaCl₂ (i = 2.47) is dissolved in 2 litres of water so that its osmotic pressure is 0.5 atm at 27ºC? (a) 3.42 g (b) 9.24 g (c)