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Acids and Bases
Chapter 15 Acids and Bases
15.2 the Acids and Bases properties of water
15.3 PH- a measure of acidity
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)
water is a 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 (2)⇄ acid(2) + base (1)
This is referred to as autoionization of water ( التأين الذاتي)
The equilibrium expression for this process is
This special equilibrium constant is referred to as the
ion-product constant for water, Kw
At 25 °C, Kw = 1.0 10−14
ثابت الحاصل الايوني للماء
The Ion-Product of Water
In pure water,
I n pure water [H 3 O + ] = [OH − ] (neutral)
In acidic solution:
In basic solution
Example 15.2 a:
Calculate the [H+] ions in ammonia, [OH-] =0.0025 M?
[H+] = 4 x10-12; [OH-] =2.5 x 10-3
[H+] < [OH-] the solution is basic
Example 15.2 b:
Calculate the [OH-] ions in 1.3 M HCl ?
[H+] = 1.3; [OH-] =7.7 x 10-15
[H+] > [OH-] the solution is Acidic
15.3 pH-A Measure of Acidity
pH of a solution: is the negative logarithm (base- 10) of the hydrogen ion (hydronium ion) concentration.
In the same manner
In pure water,
Example 15.3 a:
The [H+] = 3.2 x 10–4 M. The [H+]=1.0 x 10–3 M.
What is the pH in the two occasions.
Thus: pH is inversely proportional to [H+]
[H+] increase, pH decrease >>> more acidic
Example 15.3 b:
The [H+] = 0.76M, in nitric acid solutions
What is the pH?
pH is inversely proportional to [H+]
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
[H+] > [OH - ] [H+] = [OH-][OH-]>[H+]
Increase the basicity
Increase the acidity
pH < 7
pH = pOH = 7
pH > 7
Example 15.4 a:
The pH = 4.82 , What is the [H+] of the rain
In the calculator:
Press SHEFT → log button → (-ve ) value (4.82)=
Example 15.4 b:
The pH = 3.33 , What is the [H+] of the orange
Example 15.5 a:
The [OH-] = 2.9 x 10–4 M. What is the pH of the
pH = 10.46 > 7 BASIC (NaOH)
Example 15.5 b:
The [OH-] = 2.5 x 10–7 M. What is the pH of the
pH = 7.4 ~ 7 neutral (blood)
15.9, 15.13, 15.16, 15.18, 15.20, 15.22, 15.24, 15.26