PH of Acetylsalicylic acid???

Question

Acetylsalicylic Acid ( C10H7O2COOH ) is a medical ingredient in Aspirin. It is a weak acid.The Ka of Acetylsalicylic acid is 3.27*10^(-4).

Calculate the pH of a 0.018mol/L solution of Acetylsalicylic acid

Answer 1

HA --> H+  & A-

K = [ H+] [A-] / [HA]

3.27e-4 = [ x] [x] / [0.018 - x]

3.27e-4 [0.018 - x]= x2

5.886e-6 - 3.27e-4 x = x2

x2 + 3.27e-4 x - 5.886e-6  = 0

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x = [H+] = 0.002268

pH = 2.64