Greetings.
According to the theoretical relation [H+]=sqrt(Ka*C) the acidity of a solution of weak acid is determined by the concentration of the acid (C) and its dissosiation constant (Ka). Hence, pH=0.5*(pKa-lgC). In the case of 0.02 M aqueous solution of potassium hydrogen phtalate its experimental pH is 4.00 at room temperature while theoretical pH calculated from the relation given above is ca. 3.55. What factor causes such discrepancy?
Thanks.