Resumen de pKw Is Almost Never 14.0:: Contribution from the Task Force on the General Chemistry Curriculum
The value of -log([H+][OH-]) is not 14.00 at 25 oC in any circumstance where a student is likely to need it. If calculations are taught that use Kw then the correct value should be used, and should preferably be the Bronsted value aH+[OH-]. Values of pKw under both definitions, have been calculated from published data for various ionic strengths, temperatures, and pressures and tabulated. Calculations of pH are even then reliable only in the first decimal and approximate in the second. Texts deceive their readers when they quote 14.00 and give answers to two decimals. The value of such calculations in first year chemistry is questionable. Some suggestions are offered for teaching qualitative understanding of autoprotolysis. Plots of pKw against temperature or against the ionic strength of the solution pass through a minimum. pKw decreases with increasing pressure.
