Molality:  Boiling Point Elevation

In dilute solutions, the elevation of the boiling point is directly proportional to the number of solute molecules (or moles) in a given weight of solvent.  The effect of a nonelectrolyte dissolved in water can be calculated by:

k_b x m  =  DT_b        (k_b  =  molal B.P. constant for H₂O  =  )

 (m  =  molality of the solution)

Then, the boiling point of the solution can be calculated by:  Boiling point of solvent  +  DT_b

   Example:  What is the boiling temperature of a solution containing 30.0 g of a nonelectrolyte (MM = 180 g/mol) dissolved in 100 g (0.100 kg) of water?

k_b x m  =  x 167 m  =  0.857 ^oC  =  DT_b  

B.P. of water  +  DT_b  =  100.000 ^oC (at 1 atm)  +  0.857  =  100.857 ^oC