azeotropes , colligative properties

Azeotropes (constant boiling mixture)- and types 

The  liquid mixture, having the Same composition in liquid and vapour phase & boil at a constant temperature, is called azeotrope. 

Differentiate between minimum & maximum boiling azeotropes 

S. No.	minimum boiling azeotropes	Maximum boiling azeotropes
1	Azeotropes whose boiling point is less than either of two components present in the liquid mixture.	Azeotropes whose boiling point is more than either of two components present in the liquid mixture.
2	The non-ideal solution which show a large positive deviation from Raoult’s law form minimum boiling azeotropes at specific composition	The non-ideal solution which show a large negative deviation from Raoult’s law form minimum boiling azeotropes at specific composition
3	Example - solution showing positive deviation   Liquid mixture of 95 % ethanol + 5 % water	Example - solution showing negative deviation  Liquid mixture of 68% Nitric acid +32%water

Azeotropic matures cannot be separated into their constituents by fractional distillation. 

Colligative properties - 

  Those properties of Ideal solutions which defend only on the no. of particles of the solute (molecules or ions) dissolved in a definite amount of the solvent & do not depend on the nature of solute are called colligative properties. 

There are as follow- 

1). Relative lowering vapour pressure 

2) Elevation of boiling points 

3) Depression of freezing point  

4) osmotic pressure 

1). Relative lowering vapour pressure 

We know that when non-volatile solute is dissolved in a solvent, the vapour pressure of the solution becomes lower than that of the pure solvent. The decrease in vapour pressure of solution is called lowering of vapour pressure. Expressed by  

∆P = P10 - P1   …........................(1)  

 By applying Raoult’s law      

P1   = P10 x1    .......(2) 

∆P = P10 - P10 x1                

∆P = P10 - P10 (1-x2)       since x1=1-x2 

or ∆P = P10 - P10 +P10 x2                           

 or     ∆P = P10 x2    ….............(3) 

 So, ∆P/ P10   = (P10 - P1 )/ P10     = x2                       ,….........................  …......(4) 

 The ratio of    ∆P/ P10   = (P10 - P1 )/ P10    is called relative lowering vapour pressure. 

 Equation (4) may be written as     

∆P/ P10   =(P10 - P1 )/ P10    

                = x2 = n2 /( n1 + n2 )

For dilute solution    

(P10 - P1 )/ P10   = x2 = n2 / n1              ( since n2 is lesser than n1) 

(P10 - P1 )/ P10  = x2 = n2 / n1   = w2 x M1 /M2 x w1    ….........(5) used to calculate the molar mass of a solute. 

Problem- 1 

Problem-2