Question

The hydroxide ion concentration of an aqueous solution of 0.507 M hydrofluoric acid is [OH-]

Answer 1

HF doubleheadarrow H^+ + F^- C --- Initial concentration (mol/lit) C(1 - alpha) C alpha C alpha equilibrium concentration (mol/lit) K_a = [H^+][F^-]/[HF] = C alpha times C alpha/C(1 - alpha) = C alpha^2/(1 - alpha) alpha < < 1: 1 - alpha almostequaltoi 1 alpha = squareroot K_a/C alpha = degree of dissociation of HF [H^+] = C alpha = squareroot K_a C = squareroot 6.6 times 10^-4 times 0.507 = 0.0183(M) At 25 degree c, [H^+] [OH^-] = 10^-4 = Ionic produce of water [OH^-] = 10^-14/[H^+] = 5.46 times 10^-13 (M)