Weak acid
From Wikipedia, the free encyclopedia
- Acid-base extraction
- Acid-base reaction
- Acid-base physiology
- Acid-base homeostasis
- Dissociation constant
- Acidity function
- Buffer solutions
- pH
- Proton affinity
- Self-ionization of water
- Acids:
- Lewis acids
- Mineral acids
- Organic acids
- Strong acids
- Superacids
- Weak acids
- Bases:
A weak acid is an acid that does not completely donate all of its hydrogens when dissolved in water. These acids have higher pH compared to strong acids, which release all of their hydrogens when dissolved in water.
[edit] Explanation
Weak acids do not ionize in a solution to a significant extent; that is, if the acid was represented by the general formula HA, then in aqueous solution a significant amount of undissociated HA still remains. Weak acids in water dissociate as
The equilibrium concentrations of reactants and products are related by the Acidity constant expression, (Ka):
![\mathrm{ K_a\, =\, \frac {[H^+\,][A^-\,]}{[HA]} }](../../../../math/e/1/1/e1160cb29e6e647fa04612aee2af4f35.png)
The greater the value of Ka, the more the formation of H+ is favored, and the lower the pH of the solution. The Ka of weak acids varies between 1.8×10-16 and 55.5. Acids with a Ka less than 1.8×10-16 are weaker acids than water. Acids with a Ka of greater than 55.5 are strong acids and almost totally dissociate when dissolved in water.
[edit] Examples
The vast majority of acids are weak acids. Organic acids are a large subset of weak acids. However, there are some mineral acids in this field.
