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]
A. A
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.
Related: Chemistry — Ionic Equilibrium · All PYQ Banks