Colligative Properties?

Question

What is the boiling point (in celsius) of a 1.56m aqueous solution of CaCl2?

 

Answer 1

The solute raises the boiling point by an amount that depends on the number of particles it contributes go the solution.
Boiling point elevation is a colligative property. It depends only on the number of particles in the solution.

The formula for boiling point elevation is ΔTb=iKbm

where m is the molality of the solution, Kb is the molal boiling point elevation constant for the solvent, and i is a number related to the number of particles the solute contributes to the solution.

Non-electrolytes don't dissociate when they dissolve. Thus, one mole of glucose will have one mole of particles in solution, and i = 1.  in this case, the formula will be ΔTb=Kbm

NaCl dissociates into Na? and Cl? in water. So if you have 1 mol of NaCl, you'll have 2 mol of particles and i= 2

ΔTb=2Kbm

For CaCl2, i = 3, so ΔTb = 3 • 0.512 • 1.56 ≅ 2.4, which we add to the boiling point of water (100^oC)

 

so, the boiling point of this solution will be 102.4^oC