Elevation in Boiling Point MCQ - Practice Questions with Answers

Boiling Point: It is the temperature of a liquid at which its vapour pressure becomes equal to the atmospheric pressure. As vapour pressure of solution is lower than that of the solvents. As on addition of a non-volatile solute in a pure solvent's V.P decreases or V.P of solvent in pure state is more than that of solution. Now in order to boil the solution it is necessary to increase the temperature of solution above the B.P of pure solvent. It means B.P. of solution is always higher than B.P. of pure solvent. This increase in B.P. of solution is called elevation in B.P.(ΔT_b).

• It is also termed as Ebullioscopy.
• It is measured by Lands Berger's method and Koltrell's method.
• Suppose T^o_b and T_b are the B.P. of pure solvent and solution respectively than elevation in B.P (ΔT_b) is given as ΔT_b = T_b - T^o_b
  Here ΔT_b is directly propotional to molality of solution
  
  If molality of the solution is one, then
  
  The elevation in B.P. is also given as
  
  Molecular weight of solute can be find out as follows
  
  Here w = weight of solute
  W = weight of solvent
  K_b = molal elevation constant or ebullioscopic constant.
  M = molar mass of solute
  
  Here Lv or ΔHv = latent heat of vapourization.