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I read in my textbook that N2O5 can be prepared by reaction of HNO3 and P4O10 . A product HPO3 is also formed.

Then while discussing oxoacids of phosphorus , it said that metaphosphoric acid exists only in polymeric form.

So is there a contradiction ?

Sahil Kumar
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    $\ce{HPO3}$ does not exist as a single entity. It is actually a cyclic molecule of formula $\ce{(HPO3)_n}$. The simplest such compound is $\ce{(HPO3)3}$ which is called trimetaphosphoric acid. – Nilay Ghosh Jan 16 '23 at 05:46
  • See previous discussions: https://chemistry.stackexchange.com/questions/163305/reaction-of-phosphorus-pentoxide-with-perchloric-acid, https://chemistry.stackexchange.com/questions/163305/reaction-of-phosphorus-pentoxide-with-perchloric-acid,https://chemistry.stackexchange.com/questions/71030/what-is-the-difference-between-metaphosphoric-acid-and-phosphonic-acid,https://chemistry.stackexchange.com/questions/137045/why-is-phosphorous-pentoxide-a-dehydrating-agent?noredirect=1&lq=1 – Nilay Ghosh Jan 16 '23 at 05:47
  • https://chemistry.stackexchange.com/questions/127629/how-to-predict-the-products-of-an-inorganic-dehydration-reaction, https://chemistry.stackexchange.com/questions/71030/what-is-the-difference-between-metaphosphoric-acid-and-phosphonic-acid, https://chemistry.stackexchange.com/questions/153619/reactions-of-p2o5-and-p4o10-with-sulfuric-acid, https://chemistry.stackexchange.com/questions/54015/metaphosphoric-acid-and-water-in-cold – Nilay Ghosh Jan 16 '23 at 05:48

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$\ce{HPO3}$ is an empirical formula for a material that is indeed polymerized. Phosphoric acid is actually any of several acids containing phosphorus(V); the formula $\ce{HPO3}$ represents a limiting case for long chains, or cycles containing a finite number (at least three) of $\ce{HPO3}$ units.

What is often called phosphoric acid, the monomer $\ce{H3PO4}$, is technically orthophosphoric acid.

Oscar Lanzi
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