1. Chapter 15 Acids and Bases
15.2 the Acids and Bases properties of water
15.3 PH- a measure of acidity
Dr Laila Al-Harbi

2. Acids and Bases
Acid: Substance that produces hydrogen ions in water solution.
HCl (aq) → H+(aq) + Cl‐(aq)
Base: Substance that produces hydroxide ions in water solution.
NaOH (aq) → Na+(aq) + OH‐(aq)
An acid neutralizes a base
H+(aq) + OH‐(aq) → H2O(ℓ)
Dr Laila Al-Harbi

3. 15.2 the Acids and Bases properties of water
water is unique solvent , it can act as acid or base.
In pure water, a few molecules act as bases and a few act as acids.
acid(1) base (1) ⇄ acid(1) base (1)
This is referred to as autoionization of water
The equilibrium expression for this process is
Kc = [H3O+] [OH−]
This special equilibrium constant is referred to as the ion-product constant for water, Kw.
At 25°C, Kw = 1.0  10−14
H2O(l) + H2O(l)
H3O+(aq) + OH−(aq)
Dr Laila Al-Harbi

4. Because in pure water [H3O+] = [OH−],
Kw = [H3O+] [OH−] = 1.0  10−14
Because in pure water [H3O+] = [OH−],
[H3O+] = (1.0  10−14)1/2 = 1.0  10−7
In acidic solution
[H3O+] > [OH−]
In basic solution
[H3O+] < [OH−]
Dr Laila Al-Harbi

5. Example 15.2 Calculate the [OH-] ions in a 1.3 M HCl.
Kw = [H3O+][OH−]= 1.0  10−14
[OH−] = 1.0  10−14/ [H3O+]
[OH−] = 1.0  10−14/ 1.3
[OH−] = 7.7  10−15 M
Calculate the [H+] ions in ammonia , [OH-] = M
Kw = [H3O+] [OH−]= 1.0  10−14
[H3O+] = 1.0  10−14/ [OH−]
[H3O+] = 1.0  10−14/
[H3O+] = 4.0  10−12 M
Dr Laila Al-Harbi

6. 15-3 pH - A Measure of Acidity
pH is defined as the negative base-10 logarithm of the hydronium ion concentration.
In the same manner
In pure water,
pH + pOH = 14
pH = pOH = 7
pH = −log [H3O+] …. [H3O+] = 10-pH
pOH = −log [OH-] ….. [OH-] =10-pOH
pKw = −log [14×10-14 ] = 14
Dr Laila Al-Harbi

7. pH Range [H+]>[OH-] [H+] = [OH-] [OH-]>[H+] Acidic Basic
Neutral
[H+]>[OH-] [H+] = [OH-] [OH-]>[H+]
Acidic
Basic
Increase the acidity
Increase the basisty
pH = pOH = 7
pH >7
pH < 7
Dr Laila Al-Harbi

8. Example 15.3
The [H+]=3.2 x 10–4 M.
The [H+]=1.0 x 10–3 M. What is the pH in the two occasions.
pH = −log [H3O+]
pH = −log 3.2 x 10–4 = 3.49
pH = −log 1.0 x 10–3 = 3.00
[H3O+] increase ,pH decrease >>> more acidic
The [H+]=0.76 M, nitric acid solution ,What is the pH .
pH = −log [H3O+]
pH = −log 0.76 = 0.12
Dr Laila Al-Harbi

9. Example 15.4 The pH = 4.82 , What is the [H+] of the rain water .
[H3O+] = 10-pH
[H3O+] =
[H3O+] = 1.5 × 10–5M
The pH = 3.33 , What is the [H+] of orange juice
[H3O+] = 10-pH
[H3O+] =
[H3O+] = 4.7 × 10–4M
Dr Laila Al-Harbi

10. Example 15.5
The [OH-]=2.9 x 10–4 M. What is the pH of the NaOH solution
pOH = −log [OH-]
pOH = −log 2.9 x 10–4 = 3.54
pH + pOH = 14
pH = 14 – pOH
= =10.46
The [OH-]=2.5 x 10–7 M. What is the pH of solution the blood?
pOH = −log [OH-]
pOH = −log 2.5 x 10–7 =
pH + pOH = 14
pH = 14 – pOH
= =7.4
Dr Laila Al-Harbi

11. [H3O+] [OH-] 14 pOH pH 1.0  10−14 Acidic solution basic solution
Dr Laila Al-Harbi