Arrhenius: A base furnishes a hydroxide ion (OH-) in solution. Weak Bases in Water: Arrhenius: A base furnishes a hydroxide ion (OH-) in solution. Bronsted-Lowry: A base is a proton acceptor NH3 C6H5NH2 (CH3)2NH + H2O  NH4+ + OH- base acid conj acid conj. base + H2O  C6H5NH3+ + OH- base acid conj acid conj. base + H2O  (CH3)2NH2+ + OH- base acid conj acid conj. base The OH- ion tells us that these are Kb problems. Also: KaKb=Kw and Kw @ 25oC = 1 x10-14

Given: Kb for trimethylamine (CH3)3N is 6.4 x 10-5 Problem: Calculate the pH of a 0.05 M (CH3)3N solution. Hydrolysis Eq. Expression: (CH3)3N + H2O  (CH3)3NH+ + OH- I. C. E. 0.05 0 0 -x +x +x 0.05 - x x x try dropping to simplify the math What does x represent? [OH-] x = 1.79 x 10-3 pOH = -log[1.79 x 10-3] = 2.75 pH = 14 -2.75 = 11.25

Given: Kb for trimethylamine (CH3)3N is 6.4 x 10-5 Problem: Calculate the pH of a 0.05 M (CH3)3N solution. Hydrolysis Eq. Expression: (CH3)3N + H2O  (CH3)3NH+ + OH- I. C. E. 0.05 0 0 -x +x +x 0.05 - x x x try dropping to simplify the math What does x represent? [OH-] x = 1.79 x 10-3