Question

Question 3 What is the pH of a 0.02M solution of potassium benzoate solution (K-OOCC6H5). The pka of benzoic acid is 4.19. (Write answer to the hundredths place)

Answer 1

Ionization of CHCOONa: CH,COOK(aq) →→CH,COO-(aq) + K+(aq) Since Im ol of C.H.COONa form slmol of C.H.000 = [C,H,COOK]= 0.02 M Equation representing the ionization of CH,COO is as follows CH,000 + 1,0 —— CH,COOH + OH- Acidionization constant K of CH COOH = 104.19 = 6.4x104 CH,COO is the conjugate base of the acid CH COOH 1.0x10-14 Baseionization constant K of CH,C 6,4x10-3=1.6x10- - - - - - - - - - - - - - - - - - - - - - - - - CH,COOH + OH ----- -------------- --- CH,CO3 + H, Initial concentration (M): Change (M) -X Equilibrium concentration (M): 0.02-X + + Baseionization constant, K = 5 K - [CH.COOH)[OH-] CH,000-] 1.6x10-10 (x)(x) 0.02- x 1.6x10-10 x 0.02 x = 1.8x10M From the equilibrium table, x = [OH-] = 1.8x10 M [1,0*) - Ora 19:30* = 56210 pH=-log[H, 0+] =-log(5.6x109 ) = 8.25