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Home » Class 11 » Chemistry » Ionic Equilibrium » Salt Hydrolysis

Salt Hydrolysis

Last Updated on February 16, 2023 By Mrs Shilpi Nagpal

Salt hydrolysis is defined as the process in which a salt reacts with water to give back the acid and the base.

Salt +water ———-> Acid + Base

BA + H2O ———> HA + BOH

All salts are strong electrolytes and thus ionize completely in the aqueous solution.

(1) If the acid produced is strong and the base produced is weak.

B+ + A‾ + H2O ——-> H+ + A‾ + BOH

or

B+ + H2O ——-> H+ + BOH

In this case the cation reacts with water to give an acidic solution. This is called cationic hydrolysis.

(2) If the acid produced is weak and the base produced is strong.

B+ + A‾ + H2O ——-> HA + B+ + OH‾

or

A‾ + H2O ——-> HA + OH‾

In this case the anion reacts with water to give basic solution. This is called acidic hydrolysis.

Salt hydrolysis may be defined as the reaction of the cation or the anion of the salt with water to produce acidic or basic solution.

Depending upon the relative strength of the acid and the base produced, the resulting solution is acidic, basic or neutral.

(1) Salts of strong acid and strong base

NaCl, NaNO3, Na2SO4, KCl, KNO3 , K2SO4

NaCl + H2O ——-> NaOH + HCl

Na+ + Cl‾ + H2O ——-> Na+ + OH‾ + H+ + Cl‾

H2O ——->OH‾ + H+

It involves only ionization of water and no hydrolysis.So the solution is neutral.

The salts of strong acids and strong bases do not undergo hydrolysis and the resulting solution is neutral.

(2) Salts of weak acid and strong bases

CH3COONa, Na2CO3, K2CO3, Na3PO4

CH3COONa + H2O sign of equilibrium reactionCH3COOH + NaOH

CH3COO‾ + Na+ + H2O sign of equilibrium reactionCH3COOH + Na+ + OH‾

CH3COO‾ + H2O ——->  CH3COOH + OH‾

As it produces OH‾ ions, the solution of such a salt is alkaline in nature.

(3) Salts of strong acid and weak base

NH4Cl , CuSO4, NH4NO3 , AlCl3, CaCl2

NH4Cl + H2O sign of equilibrium reaction  NH4OH + HCl

NH4+ + Cl‾ + H2O sign of equilibrium reaction  NH4OH + H+ + Cl‾

NH4+ + H2O ——->   NH4OH + H+

As it produces H+ ions, the solution of such a salt is acidic in nature.

(4) Salts of weak acid and weak base

CH3COONH4 , AlPO4 , (NH4)2CO3

CH3COONH4  + H2O sign of equilibrium reaction CH3COOH + NH4OH

It involves both anionic and cationic hydrolysis

Hydrolysis constant

Equation for the hydrolysis of a salt (BA) may be written as:

Hydrolysis constant

Degree of Hydrolysis

The degree of hydrolysis of a salt is defined as the function of the total salt which is hydrolyse i.e.

h = No. of moles of the salt hydrolysed / Total no. of moles the salt taken

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Filed Under: Chemistry, Class 11, Ionic Equilibrium Tagged With: anionic hydrolysis, cationic hydrolysis, Degree of Hydrolysis, Hydrolysis constant, salt hydrolysis, Salts of strong acid and strong base, Salts of strong acid and weak base, Salts of weak acid and strong bases, Salts of weak acid and weak base

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Comments

  1. Soni says

    January 9, 2020 at 5:53 am

    Thanks for the notes

  2. Kelvin says

    April 8, 2020 at 11:43 am

    Thanks for these notes

  3. Amelia says

    April 17, 2020 at 2:39 am

    thank you so much Mrs Shilpi. I really appreciate this. it is so important

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