CHEM 1212K Lecture Notes - Lecture 9: Stoichiometry, Weak Base, Methylamine
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Calculate the ka of an acid (or kb of a base) , given the concentration and the percent dissociation. Problem #1: a 0. 150 m solution of acetic acid (shorthand formula = hac) is found to be 1. 086% dissociated. The equation for the dissociation of hac is: [ac ] = [h+] = 1. 629 x 10 3 m: for the [hac], we use the concentration given. We could subtract 1. 629 x 10 3 from it, but this is usually not done. Warning: you might have a teacher who does ask you to do it. You might want to check to make sure: now, we insert into the ka expression and solve: x = [(1. 629 x 10 3) (1. 629 x 10 3)] / 0. 15 x = 1. 77 x 10 5. Note: in april 2009, when the chemteam solved the above example on paper, he wrote 0. 0186 rather than 0. 01086.