The freezing point of an aqueous solution of NaHSO4 is −0.372 oC. The dissociation constant for the reaction
HSO−4→H++SO−24 is 0.4. Find the concentration of NaHSO4 in mol/kg.
[Kf for H2O=1.86 Kkgmol–1]
(Assume dilute solution and take molality = molarity)
Let the molality of NaHSO4 solution be m, then assuming molarity = molality.
HSO−4 ⟶H+ + SO−24
m(1−α) mα mα
Effective molality =[Na+]+i[HSO−4]
So, m=0.22.5=0.08 mol/kg