>> Study Material
>> IIT JEE Chemistry
>> Physical Chemistry
>> Molal Elevation Constant
Molal elevation constant :
Molal elevation constant is characteristic of a particular solvent and can be calculated from the thermodynamical relationship.
Kb = RTb2/1000Lv
where R is molar gas constant, Tb is the boiling point of the solvent on Kelvin scale and Lv the latent heat of vaporization of solvent in calories per gram.
For water Kb = 2×(373)2/1000×540 = 0.515
The molal elevation constants for some common solvents are given in the following table.
Table: Molal elevation constants of some solvents
Molal elevation constant (K kg mol−1)
If Kb, wA, ?T and wB are known, molecular mass of a non-volatile solute can be determined. The most convenient method for the determination of ?T in the laboratory is the Landsbeger method.