1. Strong and Weak Acids and Bases
Chapter 8.2

2. Strong Acids and Weak Acids
A strong acid is an acid that ionizes almost completely in water
A weak acid is an acid that only partially ionizes in water

3. Properties of Strong and Weak Acids

4. Types of Acids and Acid Strength
Oxyacids: an acid in which the donated hydrogen is attached to an oxygen atom
Organic Acids: an acid containing carbon (except H2CO3), oxygen and hydrogen atoms (also called carboxylic acids)
Binary Acids: an acid in which hydrogen is combined with a nonmetal

5. Strong Bases and Weak Bases
A strong base is a base that dissociates completely in water
- Hydroxides of group 1 and group 2 elements tend to be strong bases
A weak base is a base that only partially dissociates in water
- Many organic bases are weak bases

6. Base Ionization Constant (Kb)
The base ionization constant (Kb) is the equilibrium constant for the ionization of a base (it is also called the base dissociation constant)

7. Types of Bases and Base Strength
The table on right shows the Kb values for various weak bases at 25C.
Similar to acids, weak bases have small Kb values and strong bases have large Kb values
Organic bases: contain carbon atoms and many contain nitrogen atoms; these compounds increase the concentration of hydroxide ions in aqueous solution

8. Example 1: Write the Kb equation for ammonia

9. Water is Amphoteric
Water can behave as both an acid and a base in the same reaction
The autoionization of water is the transfer of a hydrogen ion from one water molecule to another
Hydronium ion
Hydroxide ion

10. The Ion-Product Constant for Water (Kw)
The equilibrium law equation is as follows:
As always, we omit [H2O(l)], and get the simplified equation:
This is called the ion-product constant for water, Kw:
Where,

11. the product of [H+(aq)] and [OH-(aq)]
The Importance of Kw
It is important to recognize the meaning of Kw. In any aqueous solution at 25˚C, no matter what the solution contains…
the product of [H+(aq)] and [OH-(aq)]
must always equal 1.0 x 10-14
There are three possible situations:
In a NEUTRAL solution [H+] = [OH-]
In an ACIDIC solution [H+] > [OH-]
In a BASIC solution [H+] < [OH-]
In each case at 25˚C, [H+(aq)] [OH-(aq)] = 1.0 x 10-14

12. Example 2: If a solution has a hydroxide ion concentration of 3
Example 2: If a solution has a hydroxide ion concentration of 3.5x10-5mol/L what is the hydronium ion concentration? Is the solution acidic or basic?

13. The Relationship Between Kw, Ka and Kb
For all weak acids and its conjugate base, or for a weak base and its conjugate acid, the following equation applies:
KaKb = Kw
This relationship explains the trend that: as the strength of the acid increases, the strength of its conjugate base decreases and vice versa

14. Example 3: Chlorous acid (HClO2) has a Ka of 1. 2x10-2
Example 3: Chlorous acid (HClO2) has a Ka of 1.2x10-2. What is the base ionization constant for its conjugate base?

15. pH and pOH
pH is the negative logarithm of the concentration of hydrogen ions in an aqueous solution
pH = -log[H+] and [H+] =10-pH
pOH is the negative logarithm of the concentration of hydroxide ions in an aqueous solution
pOH= -log[OH-] and [OH-]= 10-pOH
Note:
In pure water or neutral aqueous solutions,
[H+(aq)] = 1.0 x 10-7 mol/L and pH = 7
[OH-(aq)] = 1.0 x 10-7 mol/L and pOH = 7

16. Measuring pH
A pH meter is an electronic device that measures the acidity of a solution and displays the result as a pH value
An acid-base indicator is a substance that changes colour within a specific pH range

17. The Relationship of pH and pOH
Since [H+] and [OH-] are related through Kw
[H+] [OH-] =Kw
[H+] [OH-] = 1.0x10-14
pH and pOH are related through pKw
pH +pOH=pKw
pH + pOH= 14

18. Practice:
A solution has a pH of 2.6. What is the hydrogen ion concentration in the solution?
2. A solution has a hydroxide ion concentration of 3.2x10-4. What is the pH of the solution?

19. Figure 1: The pH scale showing the relationship between hydrogen ion and hydroxide ion concentrations, and pH and pOH values

20. Practice: For the following equilibrium system calculate:
a)Ka = 1.8 x 10-5 (from table)
b)Kb
c)[H+]
d)[OH-]
e)pH
f)pOH

21. Homework
Page 509 #1, 2, 3ac, 4ac, 5ace, 6ab, 7, 8, 9bd, 10