Characteristics of Polybasic Acids

In the chemical equation,acids are molecules or other entities that can donate a proton or accept an electron pair. The word “acid” comes from the Latin word “acidus,” which literally means “sour.” All acid elements have a few features, such as a sour taste and a sour smell, the ability to turn blue litmus paper red, and the ability to lose their acidity when coupled with alkaline substances. Acids have a pH ranging from 0 to 6. It’s merely an ACID, but it has a hydroxyl(-OH) group, which is a symbol for arrhenius base, thus it’s termed basic acid. Monobasic acid, dibasic acid, and polybasic acid are now classed based on the number of such groups present per molecule. Polybasic acid is defined as a basic acid that contributes more than two H+ ions (protons).

For example, H3PO4 (phosphoric acid).

What are Polybasic acids?

Polybasic acids are those that produce more than one hydronium ion per molecule, with dibasic, tribasic, and so on indicating the amount of replacement hydrogen. In the case of a few acids, such as sulphuric acid and phosphoric acid, we can see that each molecule contains more than one ionizable ion. Polybasic acids are the name given to such acids.

Ionization of Polybasic Acids

Consider the ionisation process of a common polybasic acid that goes along with it.

H2X(aq) H+(aq) + HX–(aq) 

HX– (aq)  H+(aq) + X2- (aq)

This is an example of dissociation of a dibasic acid into its constituent ions.

The balance constant for the above reaction can be given as,

Ionization

The ionisation of a chemical is the process by which neutral molecules are divided up into charged ions when exposed in a solution. According to the Arrhenius theory, acids are substances that dissociate in an aqueous media to produce hydrogen ions, H+.

Polybasic Acids

Polybasic acids can produce several hydrogen ions per molecule, with dibasic, tribasic, and so on indicating the number of hydrogen atoms that can be replaced. By looking at various acids, such as sulphuric acid and phosphoric acid, we can see that each molecule contains more than one ionizable ion. Such acids are referred to as polybasic acids. We utilise a variety of acids and bases on a daily basis, such as vinegar or acetic acid in the kitchen, boric acid in the laundry, baking soda in the kitchen, washing soda in the bathroom, and so on. Many acids and bases that we don’t use in our daily lives, such as HCl and H2SO4, as well as bases like NaOH and KOH, are used in laboratories.

The majority of these acids and bases only have one hydronium or hydroxyl ion to shed, but the majority of them have many.

Ionization of Polybasic Acids

Consider the ionisation of a common polybasic acid as follows.

H2X(aq) ⇋ H+(aq)+HX–(aq)

HX–(aq) ⇋ H+(aq)+X2-(aq)

In this case, a dibasic acid is split into its constituent ions.

The equilibrium constant for the aforementioned reaction can be expressed as,

H2X(aq) ⇋ H+(aq)+HX–(aq)

Ka1=[H+][HX–]/[H2X]

HX–(aq) ⇋ H+(aq)+X2-(aq)

Ka2=[H+][X2-]/[HX–]

As a result, the product of the dissociation constants of the constituent ions multiplied together is the dissociation polybasic acid constant.

Ka=Ka1 ×Ka2 = [H+][HX–]/ [H2X]×[H][X2-]/[HX–]=[H+2][X2-]/ [H2X]

Ka1 and Ka2 are the first and second ionisation constants of the acid H2X, respectively. We have three ionisation constants for a tribasic acid: Ka1 , Ka2, Ka3, and so on. H2SO4, H2S, H3PO4, and other polybasic acids are examples.
H2SO4 ionisation is as follows:

H2SO4 (aq) ⇋ 2H+(aq)+SO42-(aq)

Ka=[H+]² [SO42-]/[ H2SO4]

Monobasic acids are formed when most inorganic acids react with bases in such a way that one atom of the acid is linked to one atom of a metallic oxide.

Some acids, such as pyrophosphoric, have one atom that has the ability to react with two atoms of the base, and these acids are referred to as dibasic acids. This class of acids includes tartaric and malic acids, which can be found in both the plant and animal kingdoms.

Conclusion

Ka and Kb   are equilibrium constants, with a higher value indicating a more powerful acid or base. Proton donors are acids, whereas proton acceptors are bases.The donation/acceptance of only one proton is referred to as monoprotic acid/base. The donation/acceptance of more than one proton is referred to as polyprotic acid/base.