General, Organic, and Biological Chemistry Fourth Edition Karen Timberlake 10.3 Ionization of Water Chapter 10 Acids and Bases © 2013 Pearson Education, Inc. Lectures

© 2013 Pearson Education, Inc. Chapter 10 Section 3 2 In the ionization of 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(l) + H 2 O(l) H 3 O + (aq) + OH − (aq) Ionization of Water

© 2013 Pearson Education, Inc. Chapter 10 Section 3 3 The ion product constant, K w, for water at 25  C  is the product of the concentrations of the hydronium and hydroxide ions. K w = [ H 3 O + ][ OH − ]  is obtained from the concentrations in pure water. K w = [ H 3 O + ][ OH − ] K w = [1.0 x 10 −7 M][1.0 x = 1.0 x 10 −14 Ion Product of Water, K w

© 2013 Pearson Education, Inc. Chapter 10 Section 3 4 Pure Water is Neutral In pure water, the ionization of water molecules produces small but equal quantities of H 3 O + and OH − ions.

© 2013 Pearson Education, Inc. Chapter 10 Section 3 5 Acidic Solutions Adding an acid to pure water  increases the [H 3 O + ],  decreases the [OH − ], and  causes the [H 3 O + ] to exceed 1.0 x 10 −7 M.

© 2013 Pearson Education, Inc. Chapter 10 Section 3 6 Basic Solutions Adding a base to pure water,  increases the [OH − ],  decreases the [H 3 O + ], and  causes the [OH − ] to exceed 1.0 x 10 −7 M.

© 2013 Pearson Education, Inc. Chapter 10 Section 3 7 Comparison of [H 3 O + ] and [OH − ]

© 2013 Pearson Education, Inc. Chapter 10 Section 3 8 [H 3 O + ] and [OH − ] in Solutions In neutral, acidic, or basic solutions, the K w at 25  C is always 1.0 x 10 −14.

© 2013 Pearson Education, Inc. Chapter 10 Section 3 9 Guide to Calculating [H 3 O + ] and [OH − ]

© 2013 Pearson Education, Inc. Chapter 10 Section 3 10 Calculating [H 3 O + ] What is the [H 3 O + ] of a solution if [OH − ] is 5.0 x 10 −8 M? Step 1 Write the K w for water. K w = [H 3 O + ][OH − ] Step 2 Solve the K w for the unknown [H 3 O + ]. [H 3 O + ] = 1.0 x 10 −14 [OH − ] Step 3 Substitute the known [OH − ] into the equation and calculate. [H 3 O + ] = 1.0 x 10

© 2013 Pearson Education, Inc. Chapter 10 Section 3 11 If lemon juice has [H 3 O + ] of 2 x 10 −3 M, what is the [OH − ] of the solution? A. 2 x 10 −11 M B. 5 x 10 −11 M C. 5 x 10 −12 M Learning Check

© 2013 Pearson Education, Inc. Chapter 10 Section 3 12 If lemon juice has [H 3 O + ] of 2 x 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 x 10 −14 Step 2 Solve the K w for the unknown [OH − ]. [OH − ] = 1.0 x 10 −14 [H 3 O + ] Step 3 Substitute the known [H 3 O + ] into the equation and calculate. [2 x 10 −3 ] Answer is C. Solution