Salt hydrolysis

Salt hydrolysis

It is the reaction of the cation or the anion or both the ions of the salt with water to produce either acidic or basic solution. Hydrolysis is the reverse of neutralization.

 

 
 

Salt  Aqueous solution

  
  
   

(1) Hydrolysis constant: The general equation for the hydrolysis of a salt (BA),

Types of saltExp. for KhExp. for hExp. for pH
(i) Salt of weak acid and strong baseKh=Kw / KapH=–[log Kw+log Ka– log C]
(ii) Salt of strong acid and weak baseKh=Kw / KbpH=–[log Kw– log Kb+ log C]
(iii) Salt of weak acid and weak basepH=–[log Ka+ log Kw– log Kb]

 

Applying the law of chemical equilibrium, we get

, where K is the equilibrium constant.

Since water is present in very large excess in the aqueous solution, its concentration  may be regarded as constant so,

where  is called the hydrolysis constant.

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