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Home » Class 11 » Chemistry » Ionic Equilibrium » Dissociation or Ionization of Acids And Bases

Dissociation or Ionization of Acids And Bases

Last Updated on July 3, 2023 By Mrs Shilpi Nagpal

Acids like HCl, H2SO4 ,HNO3 when dissolved in water dissociates almost completely thus producing a large number of H+ ions. These acids are called strong acids.

Acids like CH3COOH , HF, H2CO3, H3PO4 dissociates only to a small extent in the aqueous solution giving small amount of H+ ions and hence are called weak acids.

Bases like NaOH , KOH dissociate almost completely in the aqueous solution producing a large number of OH‾ ions and are called strong bases.

Bases like NH4OH , Ca(OH)2 , Al(OH)3  dissociate only to a small extent in the aqueous solution and are therefore called weak bases. 

The dissociation of weak acids or weak bases in water can be represented:

CH3COOH + H2O sign of equilibrium reaction CH3COO‾ + H3O+

NH3 + H2O sign of equilibrium reaction NH4+ (aq) + OH‾(aq)

If a weak acid is represented by HA , its dissociation in water can be represented by the equilbrium:

HA + H2O sign of equilibrium reaction  A‾ (aq) + H3O+ (aq)

Applying the law of chemical equilibrium, the expression constant will be:

Equilibrium constant for dissociation of weak acid

As water is solvent, its concentration is large and remains almost constant.

HA + (aq) sign of equilibrium reaction H+ (aq) + A‾ (aq)

equilibrium constant

 

Knowing the value of the dissociation constant of the acid, Ka and the concentration of the weak acid HA taken, concentration of H3O+ or H+ in the solution can be calculated as:

HA +aq sign of equilibrium reaction  H+ (aq) + A‾ (aq)

Initial conc of HA is C mol L‾1

Initial conc of H+ is 0 M

Initial conc of A‾ is 0 M

Final conc of HA at equilibrium is (C-x) M

Final conc of H+ at equilibrium is x M

Final conc of A‾ at equilibrium is x M

equilibrium constant

Ka = x × x / C-x

Ka = x2 / C- x

x is very small as compared to the initial concentration C ,x can be neglected in comparison to C.Hence the equation is simplified to the form:

Ka = x2 / C

x= √Ka × C

The dissociation of a weak base in water can be represented by the equilibrium:

BOH + aq sign of equilibrium reaction B+ (aq) + OH‾ (aq)

Dissociation of weak base

Filed Under: Chemistry, Class 11, Ionic Equilibrium Tagged With: dissociation of acid, dissociation of base, strong acid, strong base, weak acid, weak bases

About Mrs Shilpi Nagpal

Author of this website, Mrs. Shilpi Nagpal is MSc (Hons, Chemistry) and BSc (Hons, Chemistry) from Delhi University, B.Ed. (I. P. University) and has many years of experience in teaching. She has started this educational website with the mindset of spreading free education to everyone.

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