CHEM 1002 Lecture Notes - Lecture 1: Potassium Acetate, Conjugate Acid, Weak Base
17 Jan 2015
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Acids and bases: acid base properties of salts. Calculate the ph of 2. 0 m potassium acetate, kch3coo. First, you must recognize why a solution of this salt should have a ph other than 7. 00. Although the compound can not donate h+ or oh- ions to a solution, the acetate ion is the conjugate base of a weak acid, acetic acid (ch3cooh). We therefore expect this solution to be basic. Kch3coo(s) + h2o(l) and the following equilibrium is set up: Ch3coo- (aq) + h2o(l) oh- (aq) + ch3cooh(aq) This is solved like any other acid-base equilibrium problem: And so at equilibrium, we have [oh- (aq)][ch3cooh(aq)]/[ch3coo- (aq)] = kb. To find kb for the acetate ion, remember that kb = kw/ka where kb is the base dissociation constant for the conjugate base of the acid having an acid dissociation constant ka. In this case, the acid is acetic acid, ch3cooh, for which ka = 1. 8 x 10-5.
