Question

How would Acetic Acid, HC2H3O2 and Sodium Acetate, NaC2H3O2 work as a buffer? Explain with equations.

Answer 1

An acid Buffer :

Mixture of weak acid and its salt with strong base is known as acid buffer.

Buffer solutions maitains constant pH on addition of small amount of strong acid or strong base.

Ex:

CH₃COOH(Acetic acid) + CH₃COONa (Sodium acetate)

SInce acid is weak it undergoes partial ionization and reach to equilbrium as follows,

CH₃COOH (aq.) <-----------------> H⁺ (aq.) + CH₃COO^- (aq.)

And salt is strong electrolyte undergoes forming complete ionisation as follows,

CH₃COONa (aq.) ---------------> CH₃COO^- (aq.) + Na⁺ (aq.)

Case(1) :

Add small amount of strong acid HCl,

HCl (aq.) ---------------> H⁺ (aq.) + Cl^- (aq.)

The H+ ions prouced from the strong acid are taken up by acetate ions produced from sodium acetate forming unionised acetic acid.

Hence it maintains constant pH

H⁺ (aq.) + CH₃COO^- (aq.)<------------------> CH₃COOH (aq.)

Case (2) :

Add small amount of strong base i.e NaOH,

NaOH (aq.) --------------->    Na⁺ (aq.) + OH^- (aq.)

The hydroxide ions produce by the strong base reacts with H⁺ ions priduced fro acetic acid to form neutral water molecues.

ANd hence maitains constnat pH

OH^-(aq.) + H⁺ (aq.) ----------------->H₂O (l)

In this manner a buffer solution can maintain constant pH on addition of small quatities of strong acids or strong bases.