Oxoacids of phosphorus

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

1. Hypo phosphorous acid (H3PO2) or phosphinic acid

It is preapred by the oxidation of phosphine by iodine in the presence of calculated amount of water. It is a monobasic acid.

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

2. Phosphorous acid (H3PO3) or phosphonic acid

It is prepared by hydrolysis of phosphorous trioxide (P4O6). Phosphorous acid is dibasic.
P4O6 + 6H2O ----------> 4H3PO3

phosphorous acid-(phosphonic)-(H3PO3)

3. Hypophosphoric acid (H4P2O6)

It is prepared by controlled oxidation of red phosphorous with sodium chlorite solution, when disodium salt of hypophosphoric acid is formed which then passing through cation exchanger yield hypophosphoric acid. Hypophosphoric acid is tetrabasic.
2P + 2NaClO2 + 2H2O ---------> Na2H2P2O6 + 2HCl
Na2H2P2O6 + 2H -----resin-----> H4P2O6 + 2Na - resin

hypophosphoric acid H4P2O6

4. Orthophosphoric acid (H3PO4)

It is prepared by treating P4O10 with boiled water. It is a tri basic acid.

P4O10 + 6H2O ----------> 4H3PO4

orthophosphoric acid H3PO4

5. Pyrophosphoric acid (H4p2O7)

It is prepared by heating orthophosphonic acid about 250oc. It is a tetrabasic acid.

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

Pyrophosphoric acid H4P2O7

6. Meta phosphoric (HPO3)n.

It is obtained by heating orthophosphoric acid to about 850 K. Metaphosphoric acid does not exist as monomer. It exist as cyclic trimer, cyclic tetramer or polymer.

H3PO4 -------------> HPO3 + H2O

Related articles
Oxides Of Phosphorus

Phosphine gas

1 comment:

  1. Thanks
    very nice post about oxyacids of phosphorous.

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