The weak acid where both approximations are valid

2 The weak acid where both approximations are valid 

If the acid is weak then it is possible to ignore the self ionisation of H20(l) and assume only slight ionisation of the weak acid. 

Since this equilibrium constant involves concentrations it is, by definition, a non-ideal constant, and in principle may show an ionic strength dependence. Generally the experimental measurement is the pH, found either directly from the pH of the given solution, or, more accurately, from a pH titration. The rigorous definition of pH is  

Since CH3COOH is an uncharged species, KchsCooh is expected to be approximately unity so 

for a weak acid where both approximations hold, the experimentally determined found from the fundamental experimental measurement of pH is approximately a Tyeai-However, if the experimental method had measured a concentration rather than an activity, then the experimental 

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