1. Chapter 8 Acids and Bases
8.4
Ionization of Water
Copyright © by Pearson Education, Inc.
Publishing as Benjamin Cummings

2. Ionization of Water In water,
H+ is transferred from one H2O molecule to another.
one water molecule acts as an acid, while another acts as a base.
H2O H2O H3O OH−
:O: H + H:O: H:O:H :O:H−
H H H
water water hydronium hydroxide ion (+) ion (-)

3. Pure Water is Neutral In pure water,
the ionization of water molecules produces small, but equal quantities of H3O+ and OH− ions.
molar concentrations are indicated in brackets as [H3O+] and [OH−].
[H3O+] = 1.0 x 10−7 M
[OH−] = 1.0 x 10−7 M
Copyright © by Pearson Education, Inc.
Publishing as Benjamin Cummings

4. Acidic Solutions Adding an acid to pure water increases the [H3O+].
cause the [H3O+] to exceed 1.0 x 10-7 M.
decreases the [OH−].

5. Basic Solutions Adding a base to pure water increases the [OH−].
causes the [OH−] to exceed 1.0 x 10− 7M.
decreases the [H3O+].
Copyright © by Pearson Education, Inc.
Publishing as Benjamin Cummings

6. Comparison of [H3O+] and [OH−]

7. Ion Product of Water, Kw The ion product constant, Kw, for water
is the product of the concentrations of the hydronium and hydroxide ions.
Kw = [ H3O+] [ OH− ]
can be obtained from the concentrations in pure water.
Kw = [1.0 x 10− 7 M] x [ 1.0 x 10− 7 M]
= x 10− 14

8. [H3O+] and [OH−] in Solutions
In neutral, acidic, or basic solutions,
the Kw is always 1.0 x 10−14.

9. Guide to Calculating [H3O+]

10. Calculating [H3O+]
What is the [H3O+] of a solution if [OH−] is 5.0 x 10-8 M?
STEP 1: Write the Kw for water.
Kw = [H3O+ ][OH− ] = 1.0 x 10−14
STEP 2: Rearrange the Kw expression.
[H3O+] = x 10-14
[OH−]
STEP 3: Substitute [OH−].
[H3O+] = 1.0 x = 2.0 x 10-7 M
5.0 x 10- 8

11. Learning Check
If lemon juice has [H3O+] of 2 x 10−3 M, what is the [OH−] of the solution?
1) 2 x 10−11 M
2) 5 x 10−11 M
3) 5 x 10−12 M

12. Solution 3) 5 x 10−12 M Rearrange the Kw to solve for [OH- ]
Kw = [H3O+ ][OH− ] = x 10−14
[OH− ] = 1.0 x = 5 x 10−12 M
2 x

13. Learning Check
The [OH−] of an ammonia solution is 4.0 x 10−2 M. What is the [H3O+ ] of the solution?
1) 2.5 x 10− 11 M
2) 2.5 x 10−12 M
3) 2.5 x 10−13 M

14. Solution 3) 2.5 x 10−13 M [ H3O+] = 1.0 x 10−14 = 2.5 x 10−13 M