Hydrolysis Of Salts And Buffer Solutions

Salts are formed by the neutralization of acid with base.

      Acid + Base        → Salt + Water
 HCL(aq) + NaOH(aq) → NaCl(aq) + H2O(l)

The process in which the cation or anion of the salt reacts with water to produce an acidic or an alkaline solution is called the salt hydrolysis.

            AB(aq) → A+(aq) + B-(aq)
   A+(aq) + (OH)-(aq) → AOH(aq)
    B-(aq) + H+(aq) → HB(aq)
  Salt + Water → Acid + Base

 Hydrolysis is the reverse process of neutralization.

The aqueous solution of a salt of a weak acid and a strong base is alkaline due to hydrolysis of the anion.

CH3COONa (aq) + H2O (l)     C H 3 COOH(aq) + NaOH (aq)

  
CH3COONa(aq) → CH3COO-(aq)+Na+(aq)
CH3COO-(aq) + H2O(l) ⇌ Ch3COOH(aq) + OH-(aq)

The aqueous solution of a salt of a weak base and a strong aid is acidic due to the hydrolysis of its cation.

            NH3(aq) + HCl(aq) ⇌ NH4Cl(aq)
       NH+4(aq) + H2O(l) ⇌ NH4OH(aq) + H+(aq)


The aqueous solution of salt of a weak acid and a weak base is almost neutral due to the hydrolysis of both the anion and the cation.

    CH3COOH(aq) + NH3(aq) ⇌ CH3COONH4(aq)
 CH3COO-(aq) + H2O(l) ⇌ CH3COOH(aq) + OH-(aq)
     NH+4(aq) + H2O(l) ⇌ NH4OH(aq) + H+(aq)

The aqueous solution of a salt of a strong acid and a strong base is neutral, as neither the anion nor cation undergoes hydrolysis.

   HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)

A solution which resists any change in its pH on dilution or on the addition of small amount of a strong acid or a strong alkali is called a buffer solution. It is formed by the combination of weak acid/base and its salt with strong base/acid.

Ex: Buffer solution formed by the combination of weak acetic acid and its salt with strong base like Sodium hydroxide.

Summary

Salts are formed by the neutralization of acid with base.

      Acid + Base        → Salt + Water
 HCL(aq) + NaOH(aq) → NaCl(aq) + H2O(l)

The process in which the cation or anion of the salt reacts with water to produce an acidic or an alkaline solution is called the salt hydrolysis.

            AB(aq) → A+(aq) + B-(aq)
   A+(aq) + (OH)-(aq) → AOH(aq)
    B-(aq) + H+(aq) → HB(aq)
  Salt + Water → Acid + Base

 Hydrolysis is the reverse process of neutralization.

The aqueous solution of a salt of a weak acid and a strong base is alkaline due to hydrolysis of the anion.

CH3COONa (aq) + H2O (l)     C H 3 COOH(aq) + NaOH (aq)

  
CH3COONa(aq) → CH3COO-(aq)+Na+(aq)
CH3COO-(aq) + H2O(l) ⇌ Ch3COOH(aq) + OH-(aq)

The aqueous solution of a salt of a weak base and a strong aid is acidic due to the hydrolysis of its cation.

            NH3(aq) + HCl(aq) ⇌ NH4Cl(aq)
       NH+4(aq) + H2O(l) ⇌ NH4OH(aq) + H+(aq)


The aqueous solution of salt of a weak acid and a weak base is almost neutral due to the hydrolysis of both the anion and the cation.

    CH3COOH(aq) + NH3(aq) ⇌ CH3COONH4(aq)
 CH3COO-(aq) + H2O(l) ⇌ CH3COOH(aq) + OH-(aq)
     NH+4(aq) + H2O(l) ⇌ NH4OH(aq) + H+(aq)

The aqueous solution of a salt of a strong acid and a strong base is neutral, as neither the anion nor cation undergoes hydrolysis.

   HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)

A solution which resists any change in its pH on dilution or on the addition of small amount of a strong acid or a strong alkali is called a buffer solution. It is formed by the combination of weak acid/base and its salt with strong base/acid.

Ex: Buffer solution formed by the combination of weak acetic acid and its salt with strong base like Sodium hydroxide.

Videos

References

Previous
Next