Final answer:
When OH- is added to a buffer solution of a weak acid and its conjugate base, the pH does not change much because the base neutralizes the weak acid into its conjugate partner, keeping the solution's pH stable.
Step-by-step explanation:
When a base (OH-) is added to a buffer solution containing an equal mixture of a weak acid HA and its conjugate base A-, the pH of the solution will not change significantly. This is due to the buffer action where the hydroxide ions react with the weak acid (HA), transforming it into its conjugate base (A-) and water, thus keeping the pH relatively stable. The reaction can be represented as:
HA(aq) + OH-(aq) → A-(aq) + H2O(l)
The buffer solution effectively neutralizes small amounts of the strong base, preventing large changes in pH. If we consider an acetic acid (HC2H3O2) and sodium acetate (NaC2H3O2) buffer as an example, the added OH- ions are consumed by the acetic acid in an acid-base reaction, producing water and acetate ions, with only a slight pH increase.