Definition of weak acid ionization and examples
A weak acid is an acid that is partially dissociated into its ions in an aqueous solution or water. On the other hand, a strong acid dissociates completely in its ions in water. The conjugate base of a weak acid is a weak base, while the conjugate acid of a weak base is a weak acid. At the same concentration, weak acids have a higher pH than strong acids.
Weak acid examples
Weak acids are much more common than strong acids. They are found in everyday life in vinegar (acetic acid) and lemon juice (citric acid), for example.
Common weak acids include:
|Acetic acid (ethanoic acid)||CH 3 COOH|
|Hydrogen sulfide||H 2 S|
|trichloroacetic acid||CCl 3 COOH|
|water (weak acid and weak base)||H 2 O|
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Ionization of weak acids
The reaction arrow for a strong acid ionizing in water is a simple arrow pointing from left to right. On the other hand, the reaction arrow for a weak acid ionizing in water is a double arrow, indicating both the direct and reverse reaction occur at equilibrium. (Weak Acid Examples)
At equilibrium, the weak acid, its conjugate base and the hydrogen ion are all present in the aqueous solution. The general form of the ionization reaction is:
HA ⇌ H + + A –
For example, for acetic acid, the chemical reaction takes the following form:
H 3 COOH ⇌ CH 3 COO – + H +
The acetate ion (right side or product side) is the conjugate base of acetic acid.
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Why are weak acids weak?
Whether an ion fully ionizes in water depends on the polarity or the distribution of electrons in a chemical bond. When two atoms in a bond have almost the same electronegativity values , the electrons are shared equally and spend equal amounts of time associated with each atom (a nonpolar bond).
On the other hand, when there is a significant difference in electronegativity between the atoms, there is a charge separation, where the electrons are attracted more than one atom than the other (polar bond or ionic bond).
Hydrogen atoms have a slight positive charge when linked to an electronegative element. If there is less electron density associated with hydrogen, it becomes easier to ionize and the molecule becomes more acidic (Weak Acid Examples).
Weak acids form when there is not enough polarity between the hydrogen atom and the other atom in the bond to allow easy removal of the hydrogen ion.
Another factor that affects the strength of an acid is the size of the hydrogen bonded atom. As the size of the atom increases, the strength of the bond between the two atoms decreases. This makes it easier to break the bond to release the hydrogen and increases the strength of the acid.
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