Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Chapter 8 Acids and Bases 8.3 Ionization of Water 1 In a neutral solution, [H 3 O + ] and [OH ] are equal. In acidic solutions, the [H 3 O + ] is greater than the [OH ]. In basic solutions, the [OH ] is greater than the [H 3 O + ].
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Ionization of Water In water, H + is transferred from one H 2 O molecule to another one water molecule acts as an acid, while another acts as a base H 2 O + H 2 O H 3 O + + OH water water hydronium hydroxide ion (+) ion ( ) 2
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Pure Water Is Neutral In pure water, the ionization of water molecules produces small but equal quantities of H 3 O + and OH ions molar concentrations are indicated in brackets, as [H 3 O + ] and [OH ] [H 3 O + ] = 1.0 10 7 M [OH − ] = 1.0 10 7 M 3
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Acidic Solutions Adding an acid to pure water increases the [H 3 O + ] causes the [H 3 O + ] to exceed 1.0 10 7 M decreases the [OH − ] 4
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Basic Solutions Adding a base to pure water increases the [OH − ] causes the [OH − ] to exceed 1.0 10 7 M decreases the [H 3 O + ] 5
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Comparison of [H 3 O + ] and [OH − ] 6
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Ion Product of Water, K w The ion product constant, K w, for water is the product of the concentrations of the hydronium and hydroxide ions K w = [H 3 O + ] [OH ] can be obtained from the concentrations in pure water K w = [H 3 O + ] [OH ] K w = [1.0 10 7 M] [1.0 10 7 M] = 1.0 10 14 7
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. [H 3 O + ] and [OH − ] in Solutions In neutral, acidic, or basic solutions, the K w is always 1.0 x 10 14. 8
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Guide to Calculating [H 3 O + ] 9
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Calculating [H 3 O + ] What is the [H 3 O + ] of a solution if [OH ] is 5.0 10 8 M? Step 1 Write the K w for water. K w = [H 3 O + ][OH ] = 1.0 10 14 Step 2 Solve the K w expression for unknown [H 3 O + ]. [H 3 O + ] = 1.0 10 14 [OH ] 10
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Calculating [H 3 O + ] What is the [H 3 O + ] of a solution if [OH ] is 5.0 10 8 M? Step 3 Substitute in the known [H 3 O + ] or [OH ] and calculate. [H 3 O + ] = 1.0 10 14 = 2.0 10 7 M 5.0 10 −8 11
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Learning Check If lemon juice has [H 3 O + ] of 2 10 3 M, what is the [OH ] of the solution? A. 2 10 11 M B. 5 10 11 M C. 5 10 12 M 12
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Solution If lemon juice has [H 3 O + ] of 2 10 3 M, what is the [OH ] of the solution? Step 1 Write the K w for water. K w = [H 3 O + ][OH ] = 1.0 10 14 Step 2 Solve the K w expression for unknown [OH ]. [OH ] = 1.0 10 14 [H 3 O + ] 13
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Solution If lemon juice has [H 3 O + ] of 2 10 3 M, what is the [OH ] of the solution? Step 3 Substitute in the known [H 3 O + ] or [OH ] and calculate. [OH ] = 1.0 10 14 = 5 10 12 M 2 10 3 The answer is C, 5 10 12 M. 14
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Learning Check The [OH ] of an ammonia solution is 4.0 10 2 M. What is the [H 3 O + ] of the solution? A.2.5 10 11 M B.2.5 10 12 M C.2.5 10 13 M 15
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Solution The [OH ] of an ammonia solution is 4.0 10 2 M. What is the [H 3 O + ] of the solution? Step 1 Write the K w for water. K w = [H 3 O + ][OH ] = 1.0 10 14 Step 2 Solve the K w expression for unknown [H 3 O + ]. [H 3 O + ] = 1.0 10 14 [OH ] 16
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Solution The [OH ] of an ammonia solution is 4.0 10 2 M. What is the [H 3 O + ] of the solution? Step 3 Substitute in the known [H 3 O + ] or [OH ] and calculate. [ H 3 O + ] = 1.0 10 14 = 2.5 10 13 M 4.0 10 2 The answer is C, 2.5 10 13 M. 17