Chemistry – Class XII – Formulae & Solutions – Depression in Freezing Point, Dissociation of Solute, Osmotic Pressure, Relative Lowering of Vapour Pressure, Elevation of Boiling Point, Van’t Hoff Factor, Association of Solute & Henry’s law – Very Useful f

➢ Depression in freezing point
Solutions 1


Tf = K f
m
RT20 RT2M
Kf = = A0

1000Ifusion 1000Hfusion

➢ Dissociation of solute

(A) n →
nA
1+ (n −1)
i= ( = degree of dissocition)
1




JI
PAo X A + PBo X B 
➢ P =
sol
0
Raoult’s law
(PB − PA )X B + PA
o o


➢ Osmotic pressure

 = CRT
LA
For isotonic solution, 1 = 2

1 YA YB
➢ = +
Psol PAo PNo

➢ Relative lowering of vapour pressure

PAo − P
= ( B = mole fraction of solute)
A
B
PAo

PA B PB
➢ YA = ;Y =
PA PT
B

Where YA and YB are mole fraction in vapour phase and P A = PAo X A : PB = PBo X B

➢ Elevation of boiling point

Tb = K b
m
RT20 RT2M
Kb = = A0

100I vapour 1000H vapour

Where, m = molality

MA = molecular mass of
solvent