Class 12th "Solutions"

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1.  Vapour Pressure Lowering : when we adding a vapourised solute in the normal solvent there after changed in vapour pressure is called lowering of vapour pressure. 
If any of pure solvent vapour pressure is p° and vapour pressure of solution is p, 
Than,  lowering of vapour pressure = p°-p
And relative lowering of vapour pressure = p°-p/p°
[A] Measurement of Relative Lowering of Vapour Pressure : for the measurement the Ostward and Walker's dynamic method is most important method to measurement. 

[B]   Determination of molecular mass of a solute from Relative Lowering of Vapour Pressure : The formula of the calculating the molecular mass of solute as 

Where, M' = molecular weight of solute. 
w = molar mass of solute. 
W = molar mass of solvent. 
M = molecular weight of solvent. 

•  Elevation of Boiling Point : 
    • Boiling point : it is the temperature that the substances that the vapour pressure are equavalent to the atmospheric pressure is called boiling point. 
Example : boiling Point of water is 373K (100°C) e.g. it mean that the vapour pressure of pure water is equavalent to atmospheric pressure at 373K . 
[A]  Elevation of Boiling Point : Cause of increasing the boiling point when Solute mixed in solvent. 

[B]  Calculate the Elevation of Boiling Point : The formula is given below 
•  The Malal Elevation Constant(Kb) of few Solvents :

•   Depression of Freezing Point : The difference in temperature between a solution freezing point and the freezing point of it's pure solvent. 



Some Molal Depression Constant of Solvents(Kf) : 
[A]   Determination of Molecular Mass of the Solute : 
Where, Kf = Molal depression Constant. 
∆Tf = Freezing point of solvent. 
w = molar mass of solute. 
W = molar mass of solvent. 
M' = molecular weight of solute. 


Summary : 


                        Thank you  ! 




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