Question

Tutored Practice Problem 16.4.3 couTS TOMARDS GRADI Calculate the pH of a weak acid solution (IHAlo> 100 Ka). Close Problem Çalculate the pH of a 0.330 M aqueous solution of acetic acid (CH,COOH, K-1.8x105) and the equilibrium concentrations of the weak acid and its conjugate base. pH [CH3COOH ]equilibrium = I..Hmrt CH COO lequilibrium Check & Submit Answer Show Approach

Answer 1

CH_3COOh (Weak acid) rightharpoonoverleftharpoon CH_3COO^- + H^+ initial 1 - - Reacted case - at time 't' 1 - x x x For case 'c' C(1 - x) Cx Cx K_a = [CH_3COO^-][H^+]/[CH_3COOH] K _a = C _x times C _x/C(1 - x) For K_a lessthanorequalto 10^-5 , 1 - x Approxiematelyequalto 1 K _a = Cx^2/1 x = squareroot K_a/C = squareroot 1.8 times 10^-5/6.330 = 0.00738 [CH_3COO^-] = [H^+] = 0.00738 M [CH_3COOH] = 0.330 - 0.00738 = 0.32262M P^H = -log[H^+] = -log (0.00738) P^H = 3.131 C_5H_5N (Weak base) + H_2O rightharpoonoverleftharpoon C_5H_5NH + OH^- For case 'c' at time 't' C(1 - x) - Cx Cx K_b = [C_5H_5NH][OH^-]/[C_5H_5N] K _b = Cx times Cx/C(1 - x) (Because 1 - x approxiemately 1) x = squareroot K_b/C = squareroot 1.5 times 10^- 9/0.168 = squareroot 8.928 times 10^- 9 = 9.45 times 10^-5 [OH^-] = [C_5H_5NH] = 9.45 times 10^- 5 M [C_5H_5N]