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Friday, November 20, 2020

Why "meta" phosphoric acid always exit in a polymeric form?

Meta phosphoric acids 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.

How to pridict cyclic structure given compound/oxy-acid:

If  in given compounds number of substituents are integral multiple of central atoms (except P4O6,P4O10,P4S3,P4S10,(CH2)6N4,B4Cl4) the compounds  will be cyclic structure. And number of central atoms must be three (3) or more than three.  

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

For example (2) ; H3P3O (3P+3OH+3O+3O(oxylinkage):

For example (3) ; H4P4O12   (4P+4OH+4O+4O(oxylinkage):

For example (4) ; H6P6O18   (4P+6OH+6O+6O(oxylinkage):

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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