Chapter 15 Notes1 5. weak bases: more fun stuff! equilibria & K b B(aq)+H 2 O(l)  BH 1+ (aq)+OH 1- (aq) examples of N-bases: the proton attaches to the N lone pair

Chapter 15 Notes2 questions and calculations: 1. Ammonia has K b =1.8x10 -5 ; pyridine has K b =1.7x10 -9 ; methyl amine has K b =4.4x Thus, given M solutions of each, a. pyridine is the strongest base so it has the highest pH. b. pyridine is the weakest base so it has the highest pH. c. methyl amine is the strongest base so it has the lowest pH. d. methyl amine is the strongest base so it has the highest pH. 2. Calculate the pH and the concentration of all equilibrium species in a 0.57 M solution of methylamine.

Chapter 15 Notes3 questions and calculations: 3. Consider a solution of sodium acetate Write down all the predominant species (those species present prior to any reaction). Look for any possible direct reaction between these species predominant species: Na 1+, C 2 H 3 O 2 1-, H 2 O none in this case

Chapter 15 Notes4 Write down any reactions, including the equilibrium expression and constant, that lead to secondary species, such as the autoionization of water H 2 O  H 1+ +OH 1- K W =1x secondary species: H 1+, OH 1- Look for reactions between the predominant and secondary species, and write the equations and the equilibrium expression and constant H 1+ +C 2 H 3 O 2 1-  HC 2 H 3 O 2 1/K a =1/(1.8x10 -5 )

Chapter 15 Notes5 Add the two reactions together to get the net reaction; multiply the equilibrium expressions and constants together to the the net equilibrium expression/constant. H 2 O  H 1+ +OH 1- K W =1x H 1+ +C 2 H 3 O 2 1-  HC 2 H 3 O 2 1/K a =1/(1.8x10 -5 ) C 2 H 3 O H 2 O  HC 2 H 3 O 2 +OH 1- K=K W x(1/K a )= 5.56x10 -5 in general: K w =K a xK b

Chapter 15 Notes6 questions and calculations: 4. Calculate the pH of a 0.10 M solution of sodium phenolate, NaOC 6 H 5 ; phenol is a weak acid with K a =1.3x