Oxoacids of Phosphorus

Table of Content

Introduction to Oxoacids of Phosphorus

Introduction to Oxoacids of Phosphorus

Phosphorus forms various oxoacids. They are hypophosphorous acid (H₃PO₂), Phosphorous acid (H₃PO₃), Hypophosphoric acid (H₃PO₄), pyrophosphoric acid (H₄P₂O₇) and meta phosphoric acid (HPO₂) n.

Oxoacids of Phosphorus are given in table beneath.

Name	Formula	Oxidation state of P
Hypophosphorus acid	H₃PO₂	+1
Phosphorus acid	H₃PO₃	+3
Hypophosphoric acid	H₄P₂O₆	+4
Orthophosphoric acid	H₃PO₄	-
Diphosphoric acid (Pyrophosphoric acid)	H₄P₂O₇	+5
Metaphosphoric acid	HPO₃	+5
Peroxophosphoric acid	H₃PO₅	+7

Among the oxoacids of phosphorus, orthophosphoric acid is the most critical and is utilized as a part of the produce of phosphate manures.

Hypo Phosphorous Acid (H₃PO₂) or Phosphinic Acid

It is set up by the oxidation of phosphine by iodine within the sight of figured amount of water. It is a monobasic acid.

PH₃+ 2I₂ + 2H₂O -----------> H₃PO₂ + 4 HI

Fig. 1: Hypo Phosphorous Acid

Phosphorous Acid (H₃PO₃) or Phosphonic Acid

It is set up by hydrolysis of phosphorous trioxide (P₄O₆). Phosphorous acid is dibasic in nature.

P₄O₆ + 6H₂O ----------> 4H₃PO₃

Fig. 2: Phosphorous Acid

Hypophosphoric Acid (H₄P₂O₆)

It is set up by controlled oxidation of red phosphorus with sodium chlorite arrangement when disodium salt of the hypophosphoric acid is obtained it is passed through cation exchanger to yield hypophosphoric acid. Hypophosphoric acid is tetrabasic in nature.

2P + 2NaClO₂ + 2H₂O ---------> Na₂H₂P₂O₆ + 2HCl
Na₂H₂P₂O₆ + 2H -----resin-----> H₄P₂O₆ + 2Na – resin

Fig. 3: Hypophosphoric Acid

Orthophosphoric Acid (H₃PO₄)

It is set up by treating P₄O₁₀ with bubbled water. It is a tribasic acid.

P₄O₁₀ + 6H₂O ----------> 4H₃PO₄

Fig. 4: Orthophosphoric Acid

Pyrophosphoric Acid (H₄P₂O₇)

It is set up by heating orthophosphonic acid at about 250^oC. It is a tetrabasic acid.

2H₃PO₄ ---------> H₄P₂O₇ + H₂O

Fig. 5: Pyrophosphoric Acid

Meta Phosphoric (HPO₃)n

It is formed by warming orthophosphoric acid to around 850 K. Metaphosphoric acid does not exist as monomer. It exists as cyclic trimer, cyclic tetramer or polymer.

H₃PO₄---------> HPO₃ + H₂O

Fig. 6: Metaphosphoric Acid

The structures of oxoacids of phosphorus are efficiently given ahead:

Fig. 7: Structure of oxoacids of phosphorus with their oxidation states and basic nature

The formulae of oxoacids of P can be remembered as:

Meta Acid is utilized for the acid got by the loss of one water particle.
Pyro Acid is utilized for the acid acquired by warming two atoms with the loss of one water particle.
Hypo is by and large utilized for the acid having lower oxygen content than the parent acid.

In any case, it might be noticed that metaphosphoric acid does not exist as basic monomer; it exists as cyclo metaphosphoric acid or poly metaphosphoric acid.