ACID/BASE THEORYFor the ionization of water : H2O + H2O H3O++ OH-an equilibrium expression can be written:Kw3H O ][OH==×+--.10 1014(@ 25˚C)— or —KwH ][OH×-.14(@ 25˚C)Kwis know as the ion productof water. In ANYaqueous solution this equilibrium is always present. One can always obtain theconcentration of H+from the concentration of OH-and vice versa. A strong acid will setthe value of [H+] and then [OH-] can becalculated. A strong base will setthe value of [OH-] and then [H+] can be calculated.The pH of a solution can be determine by the expression: pH = -log[H+] which means that [H+] = 10-pHIn general, the "p" in pH is really a function: p(X) = -log(X) but instead of writing p(X) we write pX.So you can easily calculate values for pOH, pKw, etc...This leads to the "-log" form of the above equation: 14 = pH + pOHThe ONLY time that [H+] = [OH-] (definition of neutral water) is when they each equal 1.0×10-7M which corresponds to a pH (andpOH for that matter) of 7.00. This is neutral pH and is the pH of pure H2O (note this is only at 25˚C, however). pH values lower than 7are acidic solutions while pH values higher than 7 are basic.
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This note was uploaded on 11/02/2008 for the course CH 301 taught by Professor Fakhreddine/lyon during the Spring '07 term at University of Texas at Austin.