CH301 - acidbase - ACID/BASE THEORY For the ionization of...

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ACID/BASE THEORY For the ionization of water : H 2 O + H 2 O H 3 O + + OH - an equilibrium expression can be written: K w3 H O ][OH == × +- - [] . 10 10 14 (@ 25˚C) — or — K w H ][OH × - . 14 (@ 25˚C) K w is know as the ion product of water. In ANY aqueous solution this equilibrium is always present. One can always obtain the concentration of H + from the concentration of OH - and vice versa. A strong acid will set the value of [H + ] and then [OH - ] can be calculated. A strong base will set the 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 -pH In 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, pK w , etc. .. This leads to the "-log" form of the above equation: 14 = pH + pOH The ONLY time that [H + ] = [OH - ] (definition of neutral water) is when they each equal 1.0 × 10 -7 M which corresponds to a pH (and pOH for that matter) of 7.00. This is neutral pH and is the pH of pure H 2 O (note this is only at 25˚C, however). pH values lower than 7 are 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.

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