Consider the dissociation equilibrium of the following weak acid HA H ⁺( aq )+ A ⁻( aq ) If the pKa of the acid is 4, then the pH of 10 mMHA solution is _ _ _ _ .(Nearest integer) [Given: The degree of dissociation can be neglected with respect to unity]

Step-by-step solution

For the weak acid dissociation HA H^+ + A^- with pKa = 4 We have Ka = 10⁻⁴. For a 10 mM (0.01 M) solution where the degree of dissociation is negligible with respect to unity, the concentration of HA remains approximately 0.01 M. The equilibrium expression gives Ka = [H^+]^2 [HA] Substituting: 10⁻⁴ = [H^+]^2 0.01 , which yields [H^+]^2 = 10⁻⁶ , so [H^+] = 10⁻³ M. Therefore, pH = - (10⁻³) = 3 .