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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); H3P3O (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.

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