Arrange the following aqueous solutions in order of decreasing boiling point (1- highest boiling; 5- lowest boiling).

0.100 m K3PO4

0.150 m CsF

H20

0.125 m SrBr2

0.250 m glucose

 

1. K₃PO₄

2. SrBr₂

3. CsF

4. Glucose

5. H₂O

Solutions show a higher boiling point compared to the pure solvent so water will have the lowest boiling point of these options. The boiling point elevation is calculated as ΔT_b = K_b x m x i where K_b is the molal boiling point elevation constant (which is the same for each of these since they are all aqueous solutions), m is the molality, and i is the van't Hoff factor which is the number of ions that the compound dissociates into.

K₃PO₄ has i = 4 because it dissociates into 3 K⁺ and PO₄^3-

CsF has i = 2 because it dissociates into Cs⁺ and F^-

SrBr₂ has i = 3 because it dissociates into Sr²⁺ and 2 Br^-

Glucose has i = 1 because it is a molecular compound and does not dissociate into ions

K₃PO₄ has m x i = 0.4

CsF has m x i = 0.3

SrBr₂ has m x i = 0.375

Glucose has m x i = 0.250

This shows that from highest to lowest boiling point the order is K₃PO₄ > SrBr₂ > CsF > Glucose > H₂O