If 0.20 mol/L CH3COOH and 0.50 mol/L CH3COO– together make a buffer solution, calculate the pH of the solution if the acid dissociation constant of CH3COOH is 1.8 × 10-5.

A buffer solution (more precisely, pH buffer or hydrogen ion buffer) is an acid or a base aqueous solution consisting of a mixture of a weak acid and its conjugate base, or vice versa. Its pH changes very little when a small amount of strong acid or base is added to it.