Consider a mixture of salt NaA and weak acid HA. Please derive the pH Henderson Hasselback equation by writing the equilibrium expression. Define the pKa. Hint: What is a buffer? Another hint: what happens when you add strong acid or base to a buffer solution? NaA(s) ---> Na+ (aq) + A-(aq) HA(aq) <---> H+ + A-(aq)