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

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

Ka = [H₃O⁺][C₆H₅O^-] / [C₆H₅OH]

1.6x10^-10 = [1.0x10^-5][1.0x10^-5] / [C₆H₅OH]

[C₆H₅OH] = (1.0x10^-5)² / 1.6x10^-10

[C₆H₅OH ] = 0.625 M