Question

What are the net equations for three steps of dissociation of phosphoric acid?

Answer 1

Answer:

Phosphoric acid (H3PO4) is a weak acid which only partially ionizes during dissociation into three steps.

Explanation:

Tons of phosphoric acid is produced every year. Most of the phosphoric acid is used in agriculture as fertilizers, insecticides and cattle feed additives. Anhydrous phosphoric acid is a white solid with melting point 42.35C to convert into a viscous liquid. Aqueous H3PO4 polyprotic in nature which means more than one protons can be donated.

H3PO4 has three steps of dissociation.  

First ionization step:

H3PO4 (Aq) <=> H+ (aq) + H2PO4- (aq)   Ka1= 7.5x10^-3  

Second ionization step

H2PO4  (aq) <=> H+ + H2PO4^-2 (aq)   Ka2=6.2x10^-8

Third ionization step

H2PO4^-2 (aq) <=> H+ (aq) + PO4^-3 (aq)   Ka3=1.7x10^-12

Answer 2

Explanation ⇒ Phosphoric Acid whose chemical formula is H₃PO₄ have three replaceable hydrogen. Hence, it is tricbasic acid.

It first remove one Hydronium ion, then removes second and then third.

You can see its disassociation equations, which are given below.

H₃PO₄ → H⁺ + H₂PO₄⁻

H₂PO₄⁻ → H⁺ + HPO₄²⁻

HPO₄²⁻ → H⁺ + PO₄³⁻

You can see these equations.

''Sometimes under presence of some acids like Concentrated Sulphuric acid, The disassociation stops to second or first reaction only.''

Hope it helps.