Create
Learn
Share

Boiling And Freezing Points

rename
Updated 2009-02-19 12:29

Overview

In a solution containing a particular solute dissolved in a particular solvent, if msolute is the molality of the solute and i is its van't Hoff factor, then the boiling point for a solution containing that solute rises by:

 

    ΔT=Kbmsolutei

 

from the boiling point for the pure solvent. Meanwhile, the freezing point for a solution containing the solute falls by:

 

    ΔT=Kfmsolutei

 

from the freezing point for the pure solvent. The molality for a particular solute is:

 

msolute=(moles of solute)/(kg of solvent)

 

and is in units of m=mol/kg. The van't Hoff factor is:

 

i=(moles of particles in solution)/(moles of solute dissolved).

 

The expected van't Hoff factor is the number of particles formed when a solute completely dissociates in the solvent. Often the observed van't Hoff factor is slightly lower than the expected van't Hoff factor due to partial dissociation of the solute.

Tables

Solvent
Boiling
Point
(deg C)
Kb
(deg C kg/mol)
Freezing
Point
(deg C)
Kf
(deg C kg/mol)
Water
(H2O)
100.00.5101.86
Carbon Tetrachloride
(CCl4)
76.55.03-22.9930
Chloroform
(CHCl3)
61.23.63-63.54.70
Benzene
(C6H6)
80.12.535.55.12
Carbon Disulfide
(CS2)
46.22.34-111.53.83
Ethyl Ether
(C4H10O)
34.52.02-116.21.79
Camphor
(C10H16O)
208.05.95179.840
memorize

 

Solution
Boiling
Point
(deg C)
Freezing
Point
(deg C)
18.00g of glucose
(CHO, 180.0g/mol)
in 150.0g of water
100.34-1.24
7.80kg of ethylene glycol
(C2H6O2, 62.1 g/mol)
in 10.0L of water
106.4-23.3
0.10m glucose
in water
100.051-0.186
fully dissociated
0.10m NaCl
in water
100.102-0.372
fully dissociated
0.10m K2SO4
in water
100.153-0.558
fully dissociated
0.10m Fe3(PO4)2
in water
100.255-0.930
fully dissociated
0.20m MgCl2
in water
100.306-1.116
fully dissociated
0.20m MgSO4
in water
100.204-0.744
fully dissociated
0.20m FeCl3
in water
100.408-1.488
fully dissociated
0.35m HCl
in water
100.357-1.302
fully dissociated
0.20m Fe(NH4)2(SO4)2
in water
100.51-1.86
memorize

Reference

Chapter 11 of "Chemistry" by Steven S. Zumdahl, 1986,
D. C. Heath and Company (ISBN=0-669-04529-2).