Chapter 14 Acids and Bases 14.5 Ionization of Water Learning Goal Use the ion product of water to calculate the [H3O+] and [OH−] in an aqueous solution. © 2014 Pearson Education, Inc.

H2O(l) + H2O(l) H3O+(aq) + OH−(aq) Ionization of Water In pure water, a forward reaction between two water molecules transfers an H+ from one water molecule to the other H2O(l) + H2O(l) H3O+(aq) + OH−(aq) H3O+ and OH− react in the reverse direction to re-form two water molecules © 2014 Pearson Education, Inc.

Water, Conjugate Acid−Base Pairs In the reaction between two water molecules, equilibrium is reached between the conjugate acid–base pairs. © 2014 Pearson Education, Inc.

Writing the Ion Product Constant of Water Using the equation for the reaction in water at equilibrium, we can write its equilibrium constant expression. H2O(l) + H2O(l) H3O+(aq) + OH−(aq) Omitting the constant concentration of pure liquid water to give the ion product constant for water, we obtain the Kw. © 2014 Pearson Education, Inc.

Writing the Ion Product of Water Experiments have determined that in pure water, the concentration of H3O+ at 25oC is 1.0 × 10−7 M. Pure water [H3O+] = 1.0 × 10−7 M Kw = [H3O+] [OH−] and [H3O+] = [OH−] = 1.0 × 10−7 M Kw = [1.0 × 10−7] [1.0 × 10−7] = 1.0 × 10−14 © 2014 Pearson Education, Inc.

Neutral, Acidic, and Basic Solution When H3O+ = OH−, the solution is neutral H3O+ > OH−, the solution is acidic H3O+ < OH−, the solution is basic In neutral, basic, and acidic solutions, Kw = 1.0 × 10−14 © 2014 Pearson Education, Inc.

Neutral, Acidic, and Basic Solution © 2014 Pearson Education, Inc.

Examples of Neutral, Acidic, and Basic Solutions © 2014 Pearson Education, Inc.

Using Kw to Calculate [H3O+] and [OH−] If we know the [H3O+] of a solution, we can use the Kw to calculate the [OH−]. Kw = [H3O+] [OH−] © 2014 Pearson Education, Inc.

Guide to Calculating [H3O+] and [OH−] © 2014 Pearson Education, Inc.

What is the [H3O+] if [OH−] is 5.0 × 10−8 M? Learning Check What is the [H3O+] if [OH−] is 5.0 × 10−8 M? © 2014 Pearson Education, Inc.

What is the [H3O+] if [OH−] is 5.0 × 10−8 M? Solution What is the [H3O+] if [OH−] is 5.0 × 10−8 M? Step 1 State the given and needed quantities. Given Need Know [OH−] = 5.0 × 10−8 M [H3O+] Kw = [H3O+] [OH−] Kw = 1.0 × 10−14 © 2014 Pearson Education, Inc.

What is the [H3O+] if [OH−] is 5.0 × 10−8 M? Solution What is the [H3O+] if [OH−] is 5.0 × 10−8 M? Step 2 Write the Kw for water and solve for the unknown [H3O+] or [OH−] © 2014 Pearson Education, Inc.

What is the [H3O+] if [OH−] is 5.0 × 10−8 M? Solution What is the [H3O+] if [OH−] is 5.0 × 10−8 M? Step 3 Substitute known [H3O+] or [OH−] into the equation and calculate © 2014 Pearson Education, Inc.