Metaphosphoric acid hydration

Metaphosphoric acid also is obtained from partial hydration of phosphorus pentoxide by dissolving it in cold water. 

Metaphosphorous acid. HPO2, is produced by atmospheric combustion of PH3, but in aqueous solution it hydrates to H3PO3. 

When brought into contact with water under various conditions phosphorus pentoxide forms one or more of differently hydrated acids. Metaphosphoric acid (q.v.) probably is the first product. 

The chemical properties of metaphosphoric acid, apart from those which are due to the fact that dehydration has proceeded to a maximum, do not differ essentially from those of the other hydrates of phosphorus pentoxide. The acid dissolves freely in certain oxygenated organic compounds—aldehydes, ketones and anhydrides, e.g, benzaldehyde, benzophenone and acetic anhydride.1 It was chlorinated but not dehydrated by phosphorus pentachloride —... 

Metaphosphoric Acid may be titrated with methyl orange, etc. irrespective of its progressive hydration (p. 175). The phenolphthalein titre, however, varies with time (see p. 176). 

In inorganic chemistry, the prefix ortho designates the most highly hydrated acid, or its salt, to contrast with the met a, or less hydrated acid or salt. For example, H3P04is orthophosphoric acid and HP03is metaphosphoric acid. These are considered in alphabetizing. 

This compound is formed only when phosphorus is burned in dry air or oxygen gas. It then appears as a white solid, like snow, which rapidly attracts moisture from the air, and passes into metaphosphoric acid, P, O, HO, or P, 0, H and this, again, soon changes, in contact with water, especially if heated, into common or hydrated phosphoric acid, P,jO, 3HO, or P, Oj, H3. The anhydrous phosphoric acid, hke the anhydrous sulphuric acid, can hardly be said to be an acid body, as it does not exhibit acid properties until it has been brought into contact with water., ... 

Metaphosphoric acid may be obtained by the spontaneous hydration of P4O10 by the air, or by adding the calculated amormt of H2O to P4O10. 

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