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# Calculate the concentration of weak acid? Given pH and Ka watch

1. Calculate the concentration of ethanoic acid with pH 4.53. (Ka = 1.74x10^-5)
No idea how to do this...
2. pH = 4.53 = -log[H+]
[H+] = 2.951x10^-5

Ka = 1.74x10^-5 = [H+][CH3COO-] / [CH3COOH]
1.74x10^-5 = [2.951x10^-5]^2 / [CH3COOH]
[CH3COOH] = 5.0 x 10^-5

I think that's correct. Not completely sure though.

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