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.
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