H30 Acetic Acid Concentration

Question

. Calculate the H3O+ concentration in a solution of acetic acid if the concentration of molecular acetic

     acid present at equilibrium is 9.97 10−3 M and K for the dissociation is 1.86 10−5. 

   CH3COOH(aq) + H2O(l) H3O+(aq) + CH3COO−(aq

Answer 1

Doing the ICE chart and plugging into the K expression at equilibrium with C being the initial acid concentration and x the amount of acid dissociated:

[H⁺][A^-]/[HA] = (x²)/[C-x) = 1.86 x 10^-5 assuming x >> 10^-7

We are given [C-x] = 9.97 x 10^-3 Molar so we can just solve for x = sqrt(1.86 x 10^-5 * 9.97 x 10^-3) =

4.31 x 10^-4 M, which is substantially larger than 10^-7

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