Measuring Ka for the BiSulfate Anion
Freezing Point Depression

There is a tutorial.............  BiSulfateTUT
There is a video........ BiSulfate.wmv

 In this experiment you will measure the Ka of the BiSulfate ion (HSO4-).    To do this you will:

  • Weigh out a freezing point apparatus with an assigned amount of distilled water
  • Obtain the freezing point of the distilled water.
  • Add a weighed amount of Potassium BiSulfate and dissolve.
  • Obtain the freezing point of this solution.
  • The freezing point depression, DT,  will give you the total molality (m) of the species in solution.  mtotal = DT/1.860
  • The computer will now assign you a Van't Hoff factor, i . This will allow you to calculate the molality of all species in solution except for the H+ ion.
  • Measure the mass of 5.00 mL (pipetted) of solution to obtain the density.  D = m/V
  • Calculate Molarities (M)   m = mol/Kg solvent;    M = mol/L
  • Calculate Ka for bisulfate.   Ka = [H+][SO4-2]/[HSO4-]

Professor R. W. Kluiber
July 2005