pH of Buffer solution
The pH of acidic and basic buffer can be calculated by Henderson – Hasselbalch equations. Consider an acidic buffer HA + A - HA H + + A - K a = [H + ] [A - ] / [HA] [H + ] = K a [HA]/[A - ] [H + ] = K a [acid]/[salt] There fore pH = -log[H + ] pH = pK a + log [salt]/[acid] when, [salt]/[acid] = 1 , pH = pK a Since pK a of an acid is a constant at constant temperature, the pH of the buffer is constant. Thus buffer capacity is maximum in a solution containing equivalent amount of acid and its salt. The pH of basic buffer is also given by Henderson – Hasselbalch equation BOH B + + OH - K b = [B + ][OH - ]/[BOH] [OH - ] = K b [BOH]/[B + ] pOH = pK b + log [salt]/[base] pH = 14 – pOH = 14 – [pK b + log [salt]/[base]]