Sulphuric acid, nitric acid, hydrochloric acid (mineral acid), carbonic acid, sulphonic acid (organic acid), and other acids are examples of such substances. Polybasic Acids are a type of acid that has a polybasic structure. These acids are those that are capable of generating more than one hydronium per molecule and are classified as polybasic. These are classified as dibasic, tribasic, and so on based on the number of hydrogens they can replace in their structure. Sulphuric acid and phosphorus acid are two examples of polybasic acids that are commonly encountered.
What are Polybasic Acids, and how do they work
The majority of the time, when inorganic acids are combined with bases, they lose one atom of acid and become united with one atom oxide, which is referred to as monoxide. However, some acids are already present in the form of pyrophosphoric acids, which have the ability to combine with a base and are thus referred to as basic acids. These types of acids can be found in both the vegetable and animal kingdoms, to name a couple of examples. Polybasic acids are also referred to as polyprotic acids in some circles. The ionisation process occurs in a stepwise manner; within each step, one proton is released, which is the constant that is used to denote each step of the ionisation process. The ionisation process is characterised by the release of one proton within each step. The magnitude of the ionising protons decreases with each successive step, with the release of numerous protons occurring as a result of this decrease.
Ionisation of Polybasic Acid
H2X(aq)H+(aq)+HX-(aq)
HX-(aq)H+(aq)+X2-(aq)
Equilibrium constant of the above reaction is
H2X(aq)H+(aq)+HX-(aq)
Ka1={[H+][HX-]}/[H2X]
HX-(aq)H+(aq)+X2-(aq)
Ka2={[H+][X2-]}/[HX-]
Therefore, the dissociation constant of the polybasic acid is defined as the product of dissociation constants of constituent ions.
Ka=Ka1×Ka2={[H+][HX-]}/[H2X]×{[H+][X2-]}/[HX-]
Ka=[H+]2[X2-]/[H2X]
Here,
Ka1= first ionisation constant of H2X
Ka2 = second ionisation constant of H2X
Conclusion
Therefore it can be concluded, Because of the extremely strong covalent bond between carbon and hydrogen in Acetic acid, the basicity of the acid is always one. A sufficient amount of energy cannot be provided by the solvent for proper dissociation to take place. There is only one Hydrogen ion produced as a result of this, which explains why the basicity is 1.