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Oxoacids of Phosphorus

 

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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

Hypo Phosphorous Acid

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

Phosphorous Acid

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

Hypophosphoric Acid

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

Orthophosphoric Acid

Fig. 4: Orthophosphoric Acid

Pyrophosphoric Acid (H4P2O7)

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

2H3PO4 ---------> H4P2O7 + H2O

 Pyrophosphoric Acid

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

Metaphosphoric Acid

Fig. 6: Metaphosphoric Acid

The structures of oxoacids of phosphorus are efficiently given ahead:

Structure of oxoacids of phosphorus with their oxidation states and basic nature

Structure of oxoacids of phosphorus with their oxidation states and basic nature

Structure of oxoacids of phosphorus with their oxidation states and basic nature

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.

Forms of Metaphosphoric Acid Forms of Metaphosphoric Acid

Fig. 8: Forms of Metaphosphoric Acid

Fig. 8: Forms of Metaphosphoric Acid


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Oxoacids of Phosphorus


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