What is the boiling point of an aqueous solution that freezes at -5.5 °C?

Question

The equation that was given in class doesn't make sense I need some guidance on how to solve this problem.

Answer 1

Hi Gio,

 

Both freezing point depression and boiling point elevation are colligative properties, so they follow essentially the same equations which are of the form

 

ΔT = k_f m i

 

where

k_f is the freezing point depression constant (or boiling point elevation constant)

m is the molality of the solute

i is the van't Hoff factor (the number of particles per mole of the solute)

 

Since this is one solution, the values for m and i are the same. So the b.p. elevation will be

 

(-5.5°C)×(b.p. elevation constant)/(f.p. depression constant)

 

Add that to the normal b.p. of water, and there you go.

 

Jim S.