An aqueous solution contains 0.02 M of a strong acid HCl and 0.06 M of a weak monoprotic acid HA . The dissociation constant of HA is K_a = 1.0 10⁻⁵ . The osmotic pressure of this mixture at 300 K is _______ 10⁻² bar (nearest integer). [Given : R = 0.083 L bar K ⁻¹ mol ⁻¹ ]

Step-by-step solution

The solution contains a strong acid ( HCl ) and a weak acid ( HA ). HCl dissociates completely: HCl H ^+ + Cl ^- Concentration of H ^+ from HCl = 0.02 M Concentration of Cl ^- = 0.02 M The weak acid HA dissociates as: HA H ^+ + A ^- Due to the common ion effect from the strong acid HCl , the dissociation of HA is heavily suppressed. Let the amount of HA dissociated be x . K_a = [ H ^+][ A ^-] [ HA ] = (0.02 + x)(x) 0.06 - x 0.02 x 0.06 1.0 10⁻⁵ = x 3 x = 3.0 10⁻⁵ M Since x is extremely small compared to 0.02 and 0.