Phenol Equalibrium

Question

Phenol, C6H5OH, partially dissociates in water as shown.

C6H5OH(aq) + H2O(l) H3O+(aq) + C6H5O−(aq)

If Ka is 1.6 10−10 and the concentrations of H3O+(aq) and C6H5O−(aq) are both 1.0 10−5 M at equilibrium, what would be the concentration of phenol?

Answer 1

K_A = [H⁺][Ph^-]/[Ph]

Let C be the initial phenol concentration:

K_A = (1 x 10^-5)²/(C - 1x10^-5) (Assuming 10^-5 is large compared to 10^-7 H⁺) (It can be included, but not within significance.)

rearranging

C = (1 x 10^-5)²/K_A + 10^-5 (The 10^-5 added is well negligible as well)

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