Acids and Bases: Ionization Constants
| Home |
| Table of Contents |
| Introduction |
| Molecular
Structure |
| Ionization
Constants |
| Salts |
| Buffers |
| Lewis Theory |
GOAL(s):
- Write ionization constant expressions for acids and bases
- Compare strengths of acids and bases using ionization constant values
- Calculate the ionization constant of an acid or base from the pH of an aqueous solution of known concentration
- Calculate the expected pH of an acid or base solution using the ionization constant
- Determine the relationship between ionization consants of conjugate acid-base pairs
- Predict whether an acid-base reaction will be product or reactant favored
How strong is a strong acid?
An acid or base's strength refers to its degree of ionization. A strong acid will completely ionize in water while a weak acid will only partially ionize.
Since there are different degrees of ionization, there are different levels of weakness. Fortunately, there is a simple quantitative way of expressing this.
Since the ionization of a weak acid is an equilibrium, a chemical equation and an equilibrium constant expression can be written:
The equilibrium constant for the ionization of an acid is called
the acid ionization constant (Ka)
.
Complete
the following sentence:
A
stronger acid will be a better proton donor, forcing the equilibrium
to the right. This produces more hydronium ions and conjugate base.
How will this affect Ka?
Good!
A strong acid is a better proton donor, resulting in more products.
Since the concentration of the products is in the numerator of the
Ka expression, the stronger the acid,
the larger the Ka.
A similar expression can be written for bases:
The equilibrium constant for the ionization of a base is called
the base ionization constant (Kb)
.
Click
on the strongest base in the list below by comparing their Kb
values.
|
|
Kb |
 Ammonia,
NH3 |
1.8 x 10-5 |
| Hydroxylamine,
HONH2 |
9.1 x 10-9 |
| Ethylamine,
C2H5NH2 |
4.3 x 10-4 |
