increasing boiling points?

Question

Can someone explain to me why this is the order of increasing boiling points. I also don't get why glycerine and KBr have the same boiling points.
0.030 m phenol (C6H5OH) < 0.040 m glycerine = 0.020 m KBr


Adrenaline is the hormone that triggeres release of extra glucose molecules in times of stress or emergency. A solution of 0.64 g of adrenaline in 36.0 g of CCl4 causes an elevation of 0.49 C in the boiling point. What is the molar mass of adrenaline?

Can someone help me check if the answer is correct.
For this question I got 182 g/mol.
I found the molality = (0.49)/(5.02) = 0.0976 m
I found the mole = (0.0360)(0.0976) = 0.00351 mol
I found molar mass = (0.64)/(0.00351) = 182 g/mol

Answer 1

KBr will dissolve into two ions when in water, so its effect is double that of glycerine. Therefore at the same molality, KBr would have twice the impact on the boiling temp than glycerine. Usually, you put an i factor (Van't Hoff's factor) in your elevation equation: dT = k*m*i. i=1 for glycerine because it is molecular and not ionic, but i=2 for KBr. In reality, i might not be an integer for KBr because it will not ionize 100% in H2O (though very close). Van't Hoff factors are known for many solutes, but if not given in a problem, then normally you would assume an integer value. If you have something like CaCl2, then i=3 (unless actual value is known).

You calculation of the molar mass of adrenaline is correct...the true value of adrenaline (epinephrine) is 183.

Answer 2

First off, other readers of your question may not know that you are talking about solutions of phenol, glycerine, and KBr in water. Second, KBr is ionized in water into K+ and Br- ions. Thus a 0.020m solution in KBr is 0.040m in ions.

Second, we can only assume you are correct that 5.02degC/m is the molal boiling point elevation constant for CCl4. Your result agrees with the known mol wt. of adrenalin of 183.