1. How is pH defined?
The pH of a solution is the negative logarithm of the hydrogen-ion concentration. The pH may be represented mathematically, using the following equation:
pH = –log[H+]
In pure water or a neutral solution, [H+] = 1 × 10–7M, and the pH is 7.
pH = –log(1 × 10–7)
= –(log 1 × log 10–7)
= –(0.0 + (–7.0))
= 7.0
If the [H+] of a solution is greater than 1 × 10–7M, the pH is less than 7.0. If the [H+] of the solution is less than 1 × 10–7M, the pH is greater than 7.0.

2. Sample problem: Calculating pH
What is the pH of a solution with a hydrogen-ion concentration of 4.2 × 10–10M?
(contd.)

3. Sample problem: Calculating pH
Calculate the pH of a solution with a hydroxide concentration of 1.2 × 10–3M.

5. How are [H+] and [OH–] related in an aqueous solution?
The reaction in which water molecules produce ions is called the self-ionization of water. This reaction can be written as a simple dissociation.
H2O(l) ⇄ H+(aq) + OH–(aq)
The self-ionization of water occurs to a very small extent. In pure water at 25°C, the concentration of hydrogen ions is only 1 × 10–7M. The concentration of OH– is also 1 × 10–7M because the numbers of H+ and OH– ions are equal in pure water.
Any aqueous solution in which [H+] and [OH–] are equal is a neutral solution.

6. For aqueous solutions, the product of the hydrogen-ion concentration and the hydroxide-ion concentration equals 1.0  10–14.
[H+]  [OH–] = 1.0  10–14
This equation is true for all dilute aqueous solutions at 25°C. The product of the concentrations of the hydrogen ions and the hydroxide ions in water is called the ion-product constant for water (Kw).
Kw = [H+] × [OH–] = 1.0 × 10–14
A solution in which [H+] is greater than [OH–] is an acidic solution. In acidic solutions, the [H+] is greater than 1 × 10–7M.
A basic solution is one in which [H+] is less than [OH–]. The [H+] of a basic solution is less than 1 × 10–7M. Basic solutions are also known as alkaline solutions.

7. You can use this equation to convert between pH and pOH
Kw = pH + pOH
Kw always equals 14
So..
pH + pOH = 14
You can use this equation to convert between pH and pOH 7

8. Sample problem: Calculating pH
Calculate the pH of a solution with a pOH of 12. 8

9. Sample problem: Calculating pH
Calculate the pOH of a solution with a pH of 9. 9

10. Sample problem: Calculating pH
Calculate the hydrogen ion concentration of a solution with a pH of 8.5. 10

11. Sample problem: Calculating pH
Calculate the hydrogen ion concentration of a solution with a pOH of 13.5. 11