Explain the difference between a diprotic and triprotic acid.
How does each acid ionise in water?
- I understand the difference between a diprotic and triprotic acid, though I haven't found how each acid ionises in water through extensive research.
Thanks.
Diprotic is H2A. It ionizes in two steps.
H2A ==> H^+ + HA^- and
HA^- ==> H^+ + A^2-
The triprotic is H3A and it ionizes in 3 steps.
A diprotic acid is an acid that contains two acidic hydrogen atoms, while a triprotic acid is an acid that contains three acidic hydrogen atoms. The main difference lies in the number of hydrogen ions that can be released when the acid dissolves in water.
To understand how each acid ionizes in water, it's important to know about the concept of ionization, which is the process by which an acid breaks apart into ions when added to water. In general, when an acid dissolves in water, it donates a hydrogen ion (H+) to the water molecule, resulting in the formation of hydronium ions (H3O+).
For a diprotic acid, like sulfuric acid (H2SO4), the ionization occurs in two stages. First, one of the hydrogen atoms is donated to a water molecule, resulting in the formation of a hydronium ion (H3O+) and a hydrogen sulfate ion (HSO4-). The reaction can be represented as:
H2SO4 + H2O ⇌ H3O+ + HSO4-
Next, the remaining hydrogen atom in the hydrogen sulfate ion can be donated in a similar way, leading to the formation of a second hydronium ion and a sulfate ion (SO4^2-). The reaction can be represented as:
HSO4- + H2O ⇌ H3O+ + SO4^2-
In the case of a triprotic acid, like phosphoric acid (H3PO4), ionization occurs in three stages. At each stage, one hydrogen atom is donated to a water molecule, generating a hydronium ion and a corresponding hydrogen phosphate ion. The reactions can be represented as:
H3PO4 + H2O ⇌ H3O+ + H2PO4-
H2PO4- + H2O ⇌ H3O+ + HPO4^2-
HPO4^2- + H2O ⇌ H3O+ + PO4^3-
It is important to note that the degree of ionization for each successive stage of ionization decreases, meaning that the concentration of hydronium ions decreases with each step. This is because the subsequent ionizations require the removal of hydrogen ions from negatively charged ions, which becomes energetically less favorable.