Freezing Point Chemistry

Question

Calculate the freezing point of a solution of 400.0 g AlCl₃ dissolved in 1600 g of water. The K_f value for water is 1.86 ^oC/m. 

Answer 1

∆T = imK

∆T = change in freezing point temperature = ?

i = van't Hoff factor = 4 for AlCl₃ b/c it dissociates to Al⁺ and 3 Cl^- (4 particles)

m = molality = moles solute/kg solvent = 400.0 g AlCl3/133g/mol = 3.01 mol/1.6 kg = 1.88 m

K = freezing point constant for water = 1.86º/m

∆T = (4)(1.88)(1.86) = 14º

New freezing point = 0º - 14º = -14ºC