Chapter 14 Acids and Bases 14.4 Dissociation Constants for Acids and Bases Learning Goal Write the expression for the dissociation constant of a weak acid or weak base. © 2014 Pearson Education, Inc.

dissociate completely in water, producing high concentrations of ions Strong Acids and Bases Strong acids and bases dissociate completely in water, producing high concentrations of ions HCl(aq) + H2O(l)  H3O+(aq) + Cl−(aq) NaOH(aq)  Na+(aq) + OH−(aq) have very large dissociation constants that are not usually given © 2014 Pearson Education, Inc.

Weak Acids, Dissociation Constants Weak acids and bases produce small amounts of ions in water HCHO2(aq) + H2O(l) H3O+(aq) + CHO2−(aq) partially dissociate in water and have a dissociation constant The acid dissociation constant for HCHO2 is: × © 2014 Pearson Education, Inc.

Weak Bases, Dissociation Constant Weak bases also have a dissociation constant, called the base dissociation constant, Kb. CH3NH2(aq) + H2O(l) CH3NH3+(aq) + OH−(aq) × © 2014 Pearson Education, Inc.

Ka, Kb Strength of Weak Acids, Bases The larger the Ka, Kb value for an acid or base, the larger the ratio of products to reactants the larger the concentration of ions produced the stronger the acid or base © 2014 Pearson Education, Inc.

Ka, Kb Weak Acids and Bases © 2014 Pearson Education, Inc.

Characteristics, Acids and Bases © 2014 Pearson Education, Inc.

Learning Check Write the equilibrium reaction and dissociation constant for the weak acid, HCN. © 2014 Pearson Education, Inc.

HCN(aq) + H2O(l) H3O+(aq) + CN−(aq) Solution Write the equilibrium reaction and dissociation constant for the weak acid, HCN. HCN(aq) + H2O(l) H3O+(aq) + CN−(aq) © 2014 Pearson Education, Inc.

Write the equilibrium reaction and Kb for the weak base CH3—CH2 –NH2. Learning Check Write the equilibrium reaction and Kb for the weak base CH3—CH2 –NH2. © 2014 Pearson Education, Inc.

Write the equilibrium reaction and Kb for the weak base CH3—CH2 –NH2. Solution Write the equilibrium reaction and Kb for the weak base CH3—CH2 –NH2. CH3—CH2 –NH2(aq) + H2O(l) OH−(aq) + CH3—CH2 –NH3+(aq) © 2014 Pearson Education, Inc.