Copyright©2000 by Houghton Mifflin Company. All rights reserved. 1 Chemistry FIFTH EDITION by Steven S. Zumdahl University of Illinois

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 2 Chemistry FIFTH EDITION Chapter 14 Acids and Bases

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 3 Section 14.5 Solving Weak Acid Equilibrium Problems 4 List major species in solution. 4 Choose species that can produce H + and write reactions. 4 Based on K values, decide on dominant equilibrium. 4 Write equilibrium expression for dominant equilibrium. 4 List initial concentrations in dominant equilibrium.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 4 Solving Weak Acid Equilibrium Problems (continued) 4 Define change at equilibrium (as “x”). 4 Write equilibrium concentrations in terms of x. 4 Substitute equilibrium concentrations into equilibrium expression. 4 Solve for x the “easy way.” 4 Verify assumptions using 5% rule. 4 Calculate [H + ] and pH.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 5 Let’s DO Problems # 53, 62 Let’s go through together Sample Exercise 14.8.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 6 The pH of a Mixture of Weak Acids See Sample Exercise 14.9 page 639 Let’s Do Problems # 61

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 7 Percent Dissociation (Ionization)

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 8 Let’s Do Problem 63 Note: For solutions of any weak acid HA, [H + ] decreases as [HA] 0 decreases; BUT The Percent Dissociation increases as [HA] 0 decreases. For a given weak acid, the percent dissociation Increases as the acid becomes more dilute.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 9 Figure The Effect of Dilution on the Percent Dissociation and (H+) of a Weak Acid Solution

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 10 Calculating K a from Percent Dissociation of a Weak Acid See Sample Exercise page 643 Let’s Do Problem #65 Homework: Do it!!!