Distribution Ratio

 




Distribution ratio is denoted by capital letter D. 

•  It is the ratio of total concentrations of species in organic phase ( phase 1) to the total concentrations of species in aquous phase.(phase 2) . 

•  Let us consider an example of benzoic acid   distributed between two immiscible solvents ether and water  
 We know that, Here benzoic acid is a solute and ether is organic solvent and water is aquous solvent. 

• kD= [HBz-]e /[ HBz-]a

Where, 

• [HBz-]e stands for Concentrations of benzoic acid in the ether layer. 

• [ HBz-]a stands for Concentrations of benzoic acid in the water layer. 
As we know, In aquous medium Benzoic acid undergo partial ionization. 

• HBz   ionises as    H+   + Bz- 

• By applying law of mass actionaction, the ionization constant (Ka) of benzoic acid in aquous medium is written as, 

• Ka  = [H+]a  [ Bz- ]a/ [ HBz]a
 Where suffix a - on the right hand side stands for     aquous. 


• The distribution ratio in the two immiscible solvents
Ether and water is written as, 

• D= [ HBz ] e/ [HBz]a+  [Bz-]e 

• Where suffix a and e represent 
ether and aquous layer respectively. 

•Benzoic acid is present inin
Undissociated form -[ HBz]- 
and 
Dissociated form- [ Bz-] . 

• So we can write , total concentration of benzoic     acid in all the forms in aquous medium in     denominator. 




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