K b is the boiling point elevation constant. It depends only on the SOLVENT. Exa

Question

Kb is the boiling point elevation constant. It depends only on the SOLVENT.

Example:
Na2SO4 is a soluble salt. It breaks into two Na+ cations and one SO42- anion in solution.

i = 2 + 1 = 3

CH3COOH is a weak acid. It breaks into a few CH3COO - anions and a few H+ cations.

1 < i < 2

Problem:

Match the following aqueous solutions with the appropriate letter from the column on the right.

Tb is the increase in the boiling point = Tb(solution) - Tb(pure solvent) m is the molality of the solution = (# moles solute / kg solvent) i is the "van't Hoff" factor = (# moles of solute particles / mole of solute) For nonelectrolytes: i = 1 For strong electrolytes: i = number of (cations + anions) For weak electrolytes: 1 < i < number of (cations + anions)

Explanation / Answer

dTb = Kb*m*i

since Kb is the same for each solution

then

dTb = m*i only (depends)

1)

0.17*3 = 0.51

0.15*3 = 0.45

0.16*3 = 0.48

0.53*1 = 0.53

the highets BP:

0.53 >0.51>0.48> 0.45

EG > Cr(CH3COO)2 > NiI2 > CuI2

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