Acetic acid is a weak acid whose Ka is 1.8 X 10^-5. Calculate the predicted pH v

Question

Acetic acid is a weak acid whose Ka is 1.8 X 10^-5. Calculate the predicted pH values for 1.0 M, 0.10 M, and 0.010 M acetic acid. (Hint: you will need to use an ICE table to find the concentration of H3O^+ at equilibrium.)

Explanation / Answer

CH3COOH(aq) + H2O(l) -----> CH3COO-(aq) + H3O+(aq) Ka IS DISSOCIATION CONSTANT WHICH IS CONCENTRATION OF PRODUCT/CONCENTRATION OF REACTANT. Ka= [CH3COO-] * [H3O+] / [CH3COOH] [H2O] is not included because its change in concentration is negligible. After partial dissociation, [CH3COOH] IS STILL APPROXIMATELY 1 M. [CH3COO-] = [H3O+] Ka of CH3COOH=1.8 * 10^-5 (from data book) 1.8 * 10^-5 = [H30+]^2 / 1 [H30]^2 = 1.8*10^-5 * 1 = 1.8*10^-5 [H30+]= 4.24*10^-3 pH= -log[H30+] pH= -log(4.24*10^-3) pH= 2.37 pH of 1 M acetic acid is 2.37 Similarly calculate for others just replacing 1 by 0.1 then 0.01 :)

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