Question

Why does the curve of titration of acetic acid begin at a higher pH than the curve for HCl? Why does the pH at the center of the rapidly rising region occur at a higher pH for the acetic acid curve than for the HCl curve?

Answer 1

pH is a measure of the concentration of H+ ions in the solution under study. These H+ ions are furnished by substances called Acids. Thry dissociate under aqueous conditions or with a base to produce H+ ions.

HCL is a strong acid and undergoes more dissociation (almost entirely compared to weaker acids like acetic acid. Higher the pH, less acidic is the solution. Therefore, the weaker acid i.e. the acetic acid solution has a higher pH compared to HCL solution.

The center of the rapidly rising curve indicates the equivalence point. This is the point where [Acid] =[Base]. For strong acids like HCL, titration with strong bases produces a neutral salt. For weaker acids like CH3COOH, titration with strong bases like NaOH produces a basic salt CH3COONa. The conjugate base of this salt CH3COO- reacts with water, thereby producing slightly alkaline solution with a pH>7.