The first disinfectant used by Joseph Lister was called carbolic acid.This substance now is known as phenol,C₆H₅OH (pK_a = 9.9).What is the pH of a 0.10 M solution of phenol?

Question

Quizplus · Accepted Answer

Phenol is a weak acid, and its Ka value can be calculated using the equation: Ka = [H+][C6H5OH]/[C6H5O-]
Let x be the concentration of H+ ions at equilibrium, so the concentration of C6H5O- ions is also x. Then, the concentration of C6H5OH is (0.10 - x), since it dissociates to produce H+ and C6H5O-. Therefore, we can write:
Ka = x^2/(0.10 - x)
At equilibrium, the concentration of H+ ions and C6H5O- ions will be equal, so we can simplify the equation:
Ka = x^2/0.10
Rearranging and solving for x:
x = sqrt(Ka * 0.10) = sqrt(1.3 * 10^-10 * 0.10) = 3.6 * 10^-6 M
Therefore, the pH of the solution is: pH = -log[H+] = -log(3.6 * 10^-6) = 5.5. The answer is D.

The First Disinfectant Used by Joseph Lister Was Called Carbolic