1. Hydronium Ions and Hydroxide Ions
Section 1 Aqueous Solutions and the Concept of pH
Chapter 15
Hydronium Ions and Hydroxide Ions
Self-ionization of water - two water molecules produce a hydronium ion and a hydroxide ion by transfer of a proton.
In water at 25°C, [H3O+] = 1.0 107 M and [OH] = 1.0  107 M.
The ionization constant of water
Kw = [H3O+][OH]

2. Kw = [H3O+][OH] = (1.0  107)(1.0  107) = 1.0  1014
Section 1 Aqueous Solutions and the Concept of pH
Chapter 15
Self-Ionization of Water
At 25°C,
Kw = [H3O+][OH] = (1.0  107)(1.0  107) = 1.0  1014
Kw increases as temperature increases

3. Chapter 15 Neutral, Acidic, and Basic Solutions
Section 1 Aqueous Solutions and the Concept of pH
Chapter 15
Neutral, Acidic, and Basic Solutions
Solutions in which [H3O+] = [OH] is neutral.
Solutions in which the [H3O+] > [OH] are acidic.
[H3O+] > 1.0  107 M
Solutions in which the [OH] > [H3O+] are basic.
[OH] > 1.0  107 M

4. Chapter 15 Calculating [H3O+] and [OH–]
Section 1 Aqueous Solutions and the Concept of pH
Chapter 15
Calculating [H3O+] and [OH–]
Strong acids and bases are considered completely ionized or dissociated in weak aqueous solutions.
1 mol mol mol
1.0  102 M NaOH solution has an [OH−] of 1.0  102 M
The [H3O+] of this solution is calculated using Kw.
Kw = [H3O+][OH] = 1.0  1014

5. Chapter 15 Calculating [H3O+] and [OH–]
Section 1 Aqueous Solutions and the Concept of pH
Chapter 15
Calculating [H3O+] and [OH–]
If the [H3O+] of a solution is known, the [OH] can be calculated using Kw.
[HCl] = 2.0  104 M
[H3O+] = 2.0  104 M
Kw = [H3O+][OH] = 1.0  1014

6. Some Strong Acids and Some Weak Acids
Section 1 Aqueous Solutions and the Concept of pH
Chapter 15
Some Strong Acids and Some Weak Acids

7. Chapter 15 Concentrations and Kw
Section 1 Aqueous Solutions and the Concept of pH
Chapter 15
Concentrations and Kw

8. Calculating [H3O+] and [OH–]
Section 1 Aqueous Solutions and the Concept of pH
Chapter 15
Calculating [H3O+] and [OH–]
Sample Problem A
A 1.0  104 M solution of HNO3 has been prepared for a laboratory experiment.
a. Calculate the [H3O+] of this solution.
b. Calculate the [OH–].

9. pH = log [H3O+] = log(1  107) =  (7.0) = 7.0
Section 1 Aqueous Solutions and the Concept of pH
Chapter 15
The pH Scale
pH of a solution - the negative of the common logarithm of the hydronium ion concentration, [H3O+].
pH = log [H3O+]
example: a neutral solution has a [H3O+] = 1107
The logarithm of 1107 is 7.0.
pH = log [H3O+] = log(1  107) =  (7.0) = 7.0

10. pH Values as Specified [H3O+]
Section 1 Aqueous Solutions and the Concept of pH
Chapter 15
pH Values as Specified [H3O+]

11. Section 1 Aqueous Solutions and the Concept of pH
Chapter 15
The pH Scale
pOH of a solution - the negative of the common logarithm of the hydroxide ion concentration, [OH–].
pOH = log [OH–]
example: a neutral solution has a [OH–] = 110 – 7
The pH = 7.0.
The negative logarithm of Kw at 25°C is 14.0.
pH + pOH = 14.0

12. Section 1 Aqueous Solutions and the Concept of pH
Chapter 15
The pH Scale

13. Approximate pH Range of Common Materials
Section 1 Aqueous Solutions and the Concept of pH
Chapter 15
Approximate pH Range of Common Materials

14. [H3O+], [OH–], pH and pOH of Solutions
Section 1 Aqueous Solutions and the Concept of pH
Chapter 15
[H3O+], [OH–], pH and pOH of Solutions

15. Chapter 15 Comparing pH and pOH Visual Concepts
Click below to watch the Visual Concept.
Visual Concept

16. Calculations Involving pH
Section 1 Aqueous Solutions and the Concept of pH
Chapter 15
Calculations Involving pH
There must be as many significant figures to the right of the decimal as there are in the number whose logarithm was found.
example: [H3O+] = 1  107
one significant figure
pH = 7.0

17. Using Logarithms in pH Calculations
Section 1 Aqueous Solutions and the Concept of pH
Chapter 15
Using Logarithms in pH Calculations

18. Chapter 15 Sample Problem B
Section 1 Aqueous Solutions and the Concept of pH
Chapter 15
Sample Problem B
What is the pH of a 1.0 10–3 M NaOH solution?

19. Chapter 15 pH = log [H3O+] log [H3O+] = pH [H3O+] = antilog (pH)
Section 1 Aqueous Solutions and the Concept of pH
Chapter 15
pH = log [H3O+]
log [H3O+] = pH
[H3O+] = antilog (pH)
[H3O+] = 10pH
The simplest cases are those in which pH values are integers.

20. Chapter 15 Sample Problem D
Section 1 Aqueous Solutions and the Concept of pH
Chapter 15
Sample Problem D
Determine the hydronium ion concentration of an aqueous solution that has a pH of 4.0.

21. Chapter 15 pH Calculations and the Strength of Acids and Bases
Section 1 Aqueous Solutions and the Concept of pH
Chapter 15
pH Calculations and the Strength of Acids and Bases
The pH of solutions of weak acids and weak bases must be measured experimentally.
The [H3O+] and [OH] can then be calculated from the measured pH values.

22. pH of Strong and Weak Acids and Bases
Section 1 Aqueous Solutions and the Concept of pH
Chapter 15
pH of Strong and Weak Acids and Bases

23. pH Values of Some Common Materials
Section 1 Aqueous Solutions and the Concept of pH
Chapter 15
pH Values of Some Common Materials