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Sunday, July 25, 2021

Oxy-acids of Phosphorous:

Oxy acids of Phosphorous:

On the basis of oxidation state oxidation state of phosphorous atom oxy-acid acid of phosphorous divided into to series;

(1) Phosphorous series of acids have (+3) oxidation state and which are reducing agents.

(2) Phosphoric series of acids have (+5) oxidation state and which are oxidizing agents.

Oxidation state of phosphorous atom and respective oxy-acids:

Oxidation state	Series name	Prefix of acid	Name of acids
(+1)	“us”series	Hypo	Hypophosphorous acid
(+3)	“us”series	…….	Phosphorous acid
(+4)	“ic”series	Hypo	Hypophosphoric acid
(+5)	“ic”series	…….	Phosphoric acid
(+7)/(+6)Cal/ava	“ic”series	Per	Perphosphoric acid

“Phosphorous and phosphoric acid both exist in ortho, pyro and meta form”

Common structure of oxy-acid of phosphorous:

All the phosphorous acid out four valency must have one (P=O) group by Ppi-Ppi bond and one (-OH) group and rest of two valency may be satisfied by P-(H) atoms of P-(OH) group depending upon acids. Where hydrogen of (OH) groups are ionizable and reponsible for acidic character while hydrogen of P-(H) bond non ionizable and responsible for reducing character of acid and non acidic.

(1) Phosphorous series:

(A) Hypophosphorus acid (H₃PO₂): is a monobasic acid and its neutral salt is NaH₂PO₂. There is two hydrogen atoms directly attach with phosphorous atom which are non ionazable and non polar and responsible for its reducing character and one hydrgen atom attach with oxygen atom and ionizable and polar and also reponsible for acidic character and its basicity is one.

(B) Phosphorus acid (H₃PO₃): is a dibasic acid and it have two salts one is neutral salt (Na₂HPO₂) and another is acidic salt (NaH₂PO₃).There is one hydrogen atoms directly attach with phosphorous atom which are non ionazable and non polar and responsible for its reducing character and two hydrgen atom attach with oxygen atom and ionizable and polar and also reponsible for acidic character and its basicity is two.

(C) Pyrophophorous acid(H₄P₂O₅):

(2) Phosphoric series:

(A) Phosphoric acid (H₃PO₄): is a tribasic acid and it have three salts in which one is neutral salt (Na₃PO₄) and another two are acidic salt (NaH₂PO₃) and (Na₂HPO₄).There are all three hydrgen atoms attach with oxygen atom and ionizable and polar and also reponsible for acidic character and hence its basicity is (3) three. And it is highly viscous in nature due to intermolecular hydrogen bonding in it.

(B) Pyrophosphoric acid(H₄P₂O₇):

(C) Hypophosphoric acid(H₄P₂O₆):

(D)Meta phosphoric acids (HPO₃)n: where n=3,4,5,6….. and their salts always exist in dimeric, trimeric, tetrameric or in polymeric linear as well as cyclic form, not in monomeric form due to the presence of weak (2p-3d- pi bond) bond the sodium salts of trimer and hexamer is very famous salts.

For example (1); H₆P₄O₁₃ (4P+6OH+4O+3O(oxylinkage)

For example (2); H₃P₃O₉ (3P+3OH+3O+3O(oxy-linkage):

For example (3); H₄P₄O₁₂ {4P+4OH+4O+4O(oxy-linkage)}:

For example (4); H₆P₆O₁₈ {4P+6OH+6O+6O(oxy-linkage)}:

Hexamer of meta phosphoric acid exist as sodium salt which is called sodium metaphophate or sodium polymetaphosphate and it is commercially known as "CALGON" and use as water softener.