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# Lecture5notes - 1 The Acidity Constant K a The strength of...

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Unformatted text preview: 9/8/09 1 The Acidity Constant, K a The strength of an acid is represented by its ionization constant (acidity constant), K a K a = product of concentrations of ionized species concentration of intact acid K a = The Acidity Constant, K a The K a implies the concentrations of the acid and the ions K a > 1 Ionized products greater than intact acid. K a < 1 Ionized products less than intact acid. K a >> 1 Ionization goes to completion (strong acid). (e.g., > 10 3 ) K a << 1 Ionization does not occur to an appreciable amount. (e.g., < 10 –3 ) 9/8/09 2 p K a = – log ( K a ) The Acidity Constant, K a Since the K a values for various acids have such a wide range, a more manageable way to discuss this measure of acidity is to use Compare p K a and K a Values p K a 14 12 10 8 6 4 2 0 strong acids weak acids K a 10-14 10-10 10-6 10-2 The smaller the value of the p K a the stronger the acid. -2 10 2 9/8/09 3 The Henderson-Hasselbalch Equation • pH in aqueous solutions is a function of the concentrations of acids and bases within them – equation defines pH as a function of the strength of an acid (pK a ) and the concentration of the acid and conjugate base • Allows calculation of pH given a certain conc. of acid • Allows calculation of amount of acid/base needed to obtain...
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Lecture5notes - 1 The Acidity Constant K a The strength of...

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