Class 12th "Solutions" Chapter no. 02

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RAOULT'S LAW :  
                            Raoult's law is name after 'Francois Marie Raoult' who while conducting an experiment found out that when substances were mixed in a solution the vapour pressure of the solution decreased simultaneously. The law is established in the year of 1887.

"Raoult's law the states that a solvents partial vapour pressure in a solution is equal or identical to the vapour pressure of the pure solvent multiply by mole fraction in the solution."

Equation of Raoult's Law : 

[  Psolution = Xsolvent × P°solvent  ]

Where, 
•  Psolution = vapour pressure of solution. 
•  Xsolvent = mole fraction of solvent. 
•  P°solvent = vapour pressure of the pure solvent. 


Calculation of Raoult's Law for Volatile Liquids :
              For a solution of valatile liquids, the partial vapour pressure of each component in the solution is directly proportional to it's mole fractions. 
Example : If we consider as A & B volatile solution. 
PA = P°A xA, PB = P°B xB
Where, 
•   PA = Partial pressure of A. 
•   P°A = Vapour pressure of pure A at                    that temperature. 
•   xA = Mole fraction of A in the liquid                 phase. 

Similarly, PB = P°B xB
Hence, PT = PA + .... 
PB (Dalton's law) = PA xA + ... 
[ P°B xB = P°A + xB (P°B - P°A) ]

Importance of Raoult's Law : 

•  Raoult's Law is depends on the concentration of each (A & B) components in the liquid phase. 
[  PA is proportional to XA, PB is proportional to XB = XA P°A = XB P°B ]

Limitations & Applications of Raoult's Law :

•  It is describing ideal solution. However ideal solution are hard to find and they are rare. 

•  It is applicable to solutions containing non-volatile solutes only.

•  It is not applicable to Solutes which dissociate or associate in the particular solutions. 

•  It is only for ideal solutions. 

•  It is only for very dilute solutions. 

Ideal Solutions :
Practice Questions :  
1.  Is Raoult's Law is valid for all type of solutions. Explain it. 

2.  What is volatile & non-volatile solutions. 


                         Thank you  ! 

Comments

  1. Unknown23 August 2020 at 12:17

    1: no. it doesn't apply on the all type of solution, it's only applyies on the ideal equation.

    2:Non-volatile substances exhibit a low vapor pressure and a high boiling point.

    :A volatile substance is one that evaporates or sublimates at room temperature or below.

    ReplyDelete
  2. Sachin Badoni24 August 2020 at 10:56

    Well done!

    ReplyDelete

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