Answer:
5.5
Explanation:
Phenol is a weak acid that dissociates according to the following reaction.
C₆H₅OH(aq) ⇄ C₆H₅O⁻(aq) + H⁺(aq)
The pKa is 9.90. The acid dissociation constant (Ka) is:
pKa = -log Ka
Ka = antilog -pKa = antilog -9.90
Ka = 1.26 × 10⁻¹⁰
Given the concentration of the acid, Ca = 0.10 M, and the Ka, We can find [H⁺] using the following expression.
[H⁺] = √(Ka × Ca)
[H⁺] = √(1.26 × 10⁻¹⁰ × 0.10)
[H⁺] =3.5 × 10⁻⁶ M
The pH is:
pH = -log [H⁺]
pH = -log 3.5 × 10⁻⁶
pH = 5.5
