Question

S.HCR and Na At what point in the following titration carve for a weak acid being litrated with a strong base is the pH equal to the p. of the acid? The X-atis scale goes from 0.0 ml. to 20.0 ml. The sharp rise is at 100 ml 10 Id 10.0 ml 180 ml

Answer 1

Lloy Suppose the weak a the titration reaction is suppose the weak acid is HA. So HA + ÕIH B D + H₂O for this type of titration, up to the equivalence point we can apply Henderson equation to calculate the pH. pH = pka + log [A - where ka is the acid dissociation constant Now, according to this equation when pH=pka [HA 7 I^2 = 1 + [A] = [HAJ - Meaning, pH = pka when concentration of Á is equal to that of HA. So exactly half amount of HA has been converted to :

This occurs at half – equivalence point. So, when half- amount of base has been added & (compared to total base at equivalence point) In the question, a sharp rise is observed at 10 ml & which means equivalence point occurs when 10.0mL of base has been added. So, half-equivalence point is when 500 ml base has been added . So, pH=pka at x = 5.0 ml Answer is 6 5.0 ml