Question

A buffer is prepared using the conjugate acid-base pair acetic acid and acetate ions. Write chemical equations showing the reactions that take place when H+ and OH- are added to the buffer.

Answer 1

CH3COOH + OH- > CH3COO- + H2O
AND
CH3COO- + H+ > CH3COOH

Answer 2

Buffer: CH3COONa and CH3COOH
CH3COONa exists as CH3COO- since it is a string electrolyte.
now CH3COOH is in equilibrium CH3COOH-> CH3COO- + H+.
So let us say you add an acid. Now since H+ concentration increases, The equilibrium proceeds in the reverse direction(Le Chateliers Principle).
So the reaction(Actually the equilibrium shifts) is CH3COO- + H+ -> CH3COOH. Now less acid dissociates and hence Ph is maintained.
Now let us add a base.
H+ + OH- -> H2O. Neutralization occurs.
Now H+ concentration reduces in the mixture This shifts the equilibrium to the right again Le Chatleliers principle.
So Now the reaction becomes CH3COOH-> CH3COO- + H+ .
Now more H+ is being produced so the Ph is Unchanged.