Colligative properties such as a freezing point depression constant depend on th
ID: 786781 • Letter: C
Question
Colligative properties such as a freezing point depression constant depend on the TOTAL molality of the PARTICLES in the solution. If a solution dissociates into ions when it dissolves, the molality is computed from the number of ions. For example, the molality of a solution containing 1.0 moles of Ca(NO3)2 in 1.0kg of water is "3 x 1.0 mol/kg= 3mol/kg" of perticles because Ca(NO3)2 gives Ca^2+ + 2 NO3- when it dissolves in water (3 moles of ions/mole of salt). Calculate the freezing point of a solution containing 18.8g of Na2SO4 in 465g of water. The Kf for water is 1.86C kg mol-1.
Explanation / Answer
d Tf = Kf * m * i
dTf = 1.86 * (18.8/142)/(465/1000) * 3
= 1.588
Freezing point = 0- 1.588
= -1.588 C