Calculate the freezing point of an aqueous solution containing 10.5 g of Magnesium bromide in 200 g of water, assuming complete dissociation of Magnesium bromide. [Molar mass of Magnesium bromide `= 184 g "mol"^(-1), K_f,` for water = 1.86 K kg `"mol"^(-1)` ?]

Explanation

Number of moles of `MgBr_2` = 10.5/184 = 0.0571 mole
Molality of the solution` = (0.571)/(200) xx 1000 = 0.2855 m`
vant Hoff factor i = 3 `[ because MgBr_2 to Mg^(2+) + 2Br^(-) ]`
Applying the relation :
` Delta T_f = iK_f m`
Substituting the values, we have
` Delta T_f = 2 xx 1.86 xx 0.2855 = 1.59 K`
Freezing point of the solution = 273