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