# Why is the pH scale only from 0-14? [duplicate]

Why can't there be more hydrogen ion concentration in acids or lesser hydrogen ion concentration in bases? Why should there even be any hydrogen ion concentration in alkalis? (I know pH is calculated by the negative log of H+ ion concentration.)

• From wikipedia, "For concentrated solutions of acids, especially strong acids for which pH < 0, the $H_0$ value is a better measure of acidity than the pH." $H_0$ value is the Hammett acidity function. I don't know many more details to write an exact answer. I would suppose the $pH$ scale doesn't work very well for very strong acids. We might have to use the activity of $\ce{H+}$ ions in solution instead of their concentration (as we do in ionic equilibrium calculations). Though I still don't know the complete answer. – Gaurang Tandon Feb 11 '18 at 11:46
• I am voting to close this question as a duplicate of Is a negative pH level physically possible?. The question is based on a misconception; the definition of $\pu{pH}$ does not limit itself to the closed interval $[0,14]$. The proper definition is also based on activity, not amount concentration, molality etc. It is difficult to measure highly acidic and basic solutions with usual glass electrodes (due to acid and base errors, among other things) but this is a metrological issue. – Linear Christmas Feb 11 '18 at 13:06