The pKa value of acetic acid CH3COOH is approximately 4.76.To calculate the pH of a 0.1 M acetic acid solution in equilibrium with its conjugate base acetate ion , we can use the Henderson-Hasselbalch equation:pH = pKa + log [A-]/[HA] where pH is the solution's pH, pKa is the acid dissociation constant, [A-] is the concentration of the conjugate base acetate ion , and [HA] is the concentration of the weak acid acetic acid .In this case, since the solution is in equilibrium, the concentration of acetic acid and acetate ion will be equal. Therefore, the ratio [A-]/[HA] will be 1.pH = 4.76 + log 1 pH = 4.76 + 0pH = 4.76So, the pH of a 0.1 M acetic acid solution in equilibrium with its conjugate base is approximately 4.76.