Question

A 27.2 mL sample of 0.270 M diethylamine, (C,Hz),NH, is titrated with 0.217 M hydroiodic acid. At the titration midpoint, the pH is

Answer 1

At mid point of a weak base/strong acid titration ; pOH = pko At mid point, pOH = PK, of (CH), NH =-log(6.9x10+) = 3.16 pH = 14.00-3.16 = 10.84 - - - - Before addition of acid: Concentration of (CH), NH = 0.215 M (CH), NH + H,0 – (CH), NH,* + OH- 0.215 -x +x 0.215- I(M): C(M) E(M): + Baseionization constant of (CH), NH, K = 6.9x10* [(C,H,), NH ][ OH-1 Base ionization constant, K = ! [(CH), NH] 6.9x10*= 70.215-x) x= 1.22x10-2M From the equilibrium table, [OH-] = x = 1.22x102 M Thus, [H,0) - fox - * = 82X10ⓇM pH =- 10g[H,04] =-log(8.20x10-3) = 12.09