# CHM 2046C Lecture Notes - Lecture 4: Conjugate Acid, Acid Strength, Acid Dissociation Constant

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20 Apr 2016
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2: [h+] or [oh-] depend on (1) k and (2) the ratio of acid and base concentrations, henderson-hasselbalch equation. [conj. base] ka: take the negative log of both sides of this equation: ph = pka - log. [conj. base] ph = pka + log[conj. base] [acid: ph adjusted by the ratio of acid and conjugate base, ph of buffer (ka) - use the henderson-hasselbalch, adding an acid/base to a buffer ph pk log a + [acid: preparing a buffer, it is best to choose an acid such that [h3o+] is about equal to. Ka (or ph pka) then get the exact [h3o+] by adjusting the ratio of acid to conjugate base. [conj. base] ka: effectiveness of buffers, the relative concns of acid & base should not differ by more than a factor of 10 to be reasonably affective; [base]/[acid] = 10 or [base]/[acid] = 0. 1: in fact, a buffer will be most effective when the [base]:[acid]