Chapter 8 Acids and Bases 8.3 Strengths of Acids and Bases

Strengths of Acids A strong acid completely ionizes (100%) in aqueous solutions. HCl(g) + H2O(l) H3O+ (aq) + Cl− (aq) A weak acid dissociates only slightly in water to form a few ions in aqueous solutions. H2CO3(aq) + H2O(l) H3O+(aq) + HCO3− (aq)

Strong Acids In water, the dissolved molecules of a strong acid dissociate into ions. give large concentrations of H3O+ and the anion (A-). Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Weak Acids In weak acids, only a few molecules dissociate. most of the weak acid remains as the undissociated (molecular) form of the acid. the concentrations of the H3O+ and the anion (A-) are small. HA(aq) + H2O(l) H3O(aq) + A−(aq) Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Strong and Weak Acids In an HCl solution, the strong acid HCl dissociates 100%. A solution of the weak acid CH3COOH contains mostly molecules and a few ions.

Strong Acids Strong acids make up six of all the acids. have weak conjugate bases.

Weak Acids Weak acids make up most of the acids. have strong conjugate bases.

Comparing Strong and Weak Acids

Strong Bases Strong bases are formed from metals of Groups 1A (1) and 2A (2). include LiOH, NaOH, KOH, and Ca(OH)2. dissociate completely in water. KOH(s) K+(aq) + OH−(aq)

Weak Bases Weak bases are most other bases. dissociate only slightly in water. form only a few ions in water. NH3(g) + H2O(l) NH4+(aq) + OH−(aq)

Learning Check A. HBr B. HNO2 C. NaOH D. H2SO4 E. Cu(OH)2 Identify each of the following as a strong or weak acid or base. A. HBr B. HNO2 C. NaOH D. H2SO4 E. Cu(OH)2

Solution A. HBr strong acid B. HNO2 weak acid C. NaOH strong base Identify each of the following as a strong or weak acid or base. A. HBr strong acid B. HNO2 weak acid C. NaOH strong base D. H2SO4 strong acid E. Cu(OH)2 weak base

Learning Check Identify the stronger acid in each pair. 1. HNO2 or H2S 2. HCO3− or HBr 3. H3PO4 or H3O+

Solution Identify the stronger acid in each pair. 1. HNO2 2. HBr 3. H3O+