Hydrolysis of Salt

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Hydrolysis of Salt

Published by: Nuru

Published date: 27 Jun 2021

Hydrolysis of Salt in Grade 12

Hydrolysis of Salt

Salt hydrolysis- The interaction of cation or anion of a salt with water producing acidity or alkalinity is called salt hydrolysis.

It is of four types:-

  1. Hydrolysis of salts of strong acid and weak base.
  2. Hydrolysis of salts of a weak acid and strong base.
  3. Hydrolysis of salts of a weak acid and weak base.
  4. Hydrolysis of salts of strong acid and strong base.

Explanations:-

  1. Hydrolysis of salts of strong acid and weak base.

Salts such as NH4CL, CuSO­4, FeCL3, etc belong to this type of salts which are formed from a strong acid and weak base. When any one of such salt is dissolved in water then strong acids and weak bases are formed.

Let us consider the hydrolysis of CuSO­4 in solution. It is ionized as

CuSO­4  Cu++ + SO­4++

At the same time, water gets decomposed to

H2O \rightleftharpoons H+ + OH–

Now, Cu++ combines with OH– and SO­4++ combines with H+.

CU++ + 2OH– \rightleftharpoons Cu(OH)2 (weak base)

S04– – + 2H+ \rightleftharpoons H2SO4   (strong acid)

So, all the H2SO4 can’t be neutralized by Cu(OH)2 and there may be some concentration of H+ ions in the solution is slightly acidic.

  1. Hydrolysis of salts of a weak acid and strong base.

Salt such as CH3COONa, Na2CO3,  etc belongs to this type of salts which are formed from a weak acid and strong base. When any one of such salt is dissolved in water then weak acids and strong bases are formed.

Let us consider the hydrolysis of CH3COONa in the solution it is ionized as

CH3COONa \rightleftharpoons CH3COO– + Na+

Now, CH3COO– and Na+ interact with H+ and OH– ions of the water.

CH3COO– + H+ \rightleftharpoons CH3COOH

Na+ + OH– \rightleftharpoons NaOH

CH3COOH is the weak acid so, it is partially ionized in the solution but NaOH is the strong base so, it is almost completely ionized in the solution. Since acetic acid can’t neutralize all parts of NaOH so, there may be some OH– ions remain in the solution. Therefore, the resulting solution is slightly basic.

  1. Hydrolysis of salts of a weak acid and weak base.

Salt such as CH3COONH4, (NH4)2CO3, etc belong to this type of salts. When any one of such salt is dissolved in water then weak and acid weak bases are formed.

Let us consider the hydrolysis of CH3COONH4 in solution in ionized as:

CH3COONH4 \rightleftharpoons CH3COO– + NH4+

Now, CH3COO– and NH4+ interact with H+ and OH– ion of the water,

CH3COO– + H+  \rightleftharpoons CH3COOH

NH4+ + OH– \rightleftharpoons NH4OH

CH3COOH is a weak acid so, it is also partially ionized in the solution. Similarly, NH4OH is the weak base so, it also partially ionized in the solution. There is no more concentration of either H+ ion or OH– ion remain in the remain in the solution so, the solution is almost neutral. But if acid is more ionized compared to the base then the solution will be slightly acidic and vice versa.

  1. Hydrolysis of salts of strong acid and strong base.

Salt such as NaCl, KCL, K2SO4, Na2SO4, KNO3, etc belongs to this type of salts which are formed from strong acid and strong bases.

When any one of such salt dissolved in water then formed the conjugate base of the acid conjugate acid of the base have nither tendency to give off protons hence, these ions do not interact with the water and thus hydrolysis doesn’t take place. Therefore, these salts are almost neutral.