Boiling And Freezing Points

Overview

In a solution containing a particular solute dissolved in a particular solvent, if m_solute 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=K_bm_solutei

 

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

 

    ΔT=K_fm_solutei

 

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

 

m_solute=(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)	100.0	0.51	0	1.86
Carbon Tetrachloride (CCl4)	76.5	5.03	-22.99	30
Chloroform (CHCl3)	61.2	3.63	-63.5	4.70
Benzene (C6H6)	80.1	2.53	5.5	5.12
Carbon Disulfide (CS2)	46.2	2.34	-111.5	3.83
Ethyl Ether (C4H10O)	34.5	2.02	-116.2	1.79
Camphor (C10H16O)	208.0	5.95	179.8	40
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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