text: can there be a ph greater than 15 and less than 1? in school, i have been taught ka * kb = 10 to the power of -14. however, if equilubrium constants vary with temperature then surely this value will change and in doing so allow the ph range to oncrease? got an exam tomorrow and just wondering - help greatly appreciated! actually, yes.  ph is the negative of the logarithm of the concentration of hydronium ion in aqueous solution:  ph = -log[h3o+]  so, for example, if one had a theoretical concentration of hydronium ion of 10, then ph would be -1.  and since   kw = 10^-14 = [h3o+]*[oh-]  the resulting [oh-] would be 10^-15.  the resulting ph value would be -1, and the poh 15, which would fit the equation ph + poh = 14.