Phosphotungstic acid

Phosphotungstic acid
Structure of the phosphotungstate anion
Names
Other names
Tungstophosphoric acid (TPA)
Phosphotungstic acid (PTA, PWA) 12-Phosphotungstic acid
12-Tungstophosphoric acid[1]
Dodecatungstophosphoric acid
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.108.885 Edit this at Wikidata
EC Number
  • (hydrate): 603-020-3
UNII
  • (hydrate): InChI=1S/H3O4P.H2O.36O.12W/c1-5(2,3)4;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;/h(H3,1,2,3,4);1H2;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
    Key: AVFBYUADVDVJQL-UHFFFAOYSA-N
  • [W]18%21%24(O[W]%16%18%23(O[W]56(O1)(O[W]247(O[W]9%22(O[W]%12%13(O2)(O[W]3%11%14(O[W]%17%19(O[W](O3)(O4)(O5)([O++]67[P+]%15%20[O++]89[W]%10(O[W](O[W](O%10)(O%11)(O%12)([O++]%13%14%15)[O-])(O%16)(O%17)([O++]%18%19%20)[O-])(O%21)(O%22)[O-])[O-])(O%23)[O-])[O-])[O-])(O%24)O)[O-])O)[O-])O
Properties
H3[PW12O40]
Molar mass 2880.2 g/mol (anhydrous)
Melting point 89 °C (192 °F; 362 K) (hydrate)
Hazards
GHS labelling:
GHS05: CorrosiveGHS07: Exclamation markGHS09: Environmental hazard
Danger
H302, H314, H411
P260, P264, P270, P273, P280, P301+P312, P301+P330+P331, P303+P361+P353, P304+P340, P305+P351+P338, P310, P321, P330, P363, P391, P405, P501
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Phosphotungstic acid (PTA) or tungstophosphoric acid (TPA), is a heteropoly acid with the chemical formula H3PW12O40]. It forms hydrates H3[PW12O40]·nH2O. It is normally isolated as the n = 24 hydrate but can be desiccated to the hexahydrate (n = 6).[2] EPTA is the name of ethanolic phosphotungstic acid, its alcohol solution used in biology. It has the appearance of small, colorless-grayish or slightly yellow-green crystals, with melting point 89 °C (24 H2O hydrate). It is odorless and soluble in water (200 g/100 ml). It is not especially toxic, but is a mild acidic irritant. The compound is known by a variety of names and acronyms (see 'other names' section of infobox).

In these names the "12" or "dodeca" reflects the fact that the anion contains 12 tungsten atoms. Some early workers who did not know the structure[3] called it phospho-24-tungstic acid, formulating it as 3H2O·P2O5 24WO3·59H2O, (P2W24O80H6)·29H2O, which correctly identifies the atomic ratios of P, W and O. This formula was still quoted in papers as late as 1970.[4]

Phosphotungstic acid is used in histology as a component for staining of cell specimens, often together with haematoxylin as PTAH. It binds to fibrin, collagen, and fibres of connective tissues, and replaces the anions of dyes from these materials, selectively decoloring them.

Phosphotungstic acid is electron dense, opaque for electrons. It is a common negative stain for viruses, nerves, polysaccharides, and other biological tissue materials for imaging by a transmission electron microscope.

  1. ^ Cotton FA, Wilkinson G (1966). Advanced inorganic chemistry: a comprehensive text (2nd ed.). New York: Wiley. ISBN 0470175583. LCCN 66020662. OCLC 85904497.
  2. ^ Cite error: The named reference Dias was invoked but never defined (see the help page).
  3. ^ Hsein W (1920). "Contribution to the chemistry of phosphomolybdic acids, phosphotungstic acids and allied substances". Journal of Biological Chemistry. 43: 189–220. doi:10.1016/S0021-9258(18)86325-6.
  4. ^ Quintarelli G, Zito R, Cifonelli JA (November 1971). "On phosphotungstic acid staining. I". The Journal of Histochemistry and Cytochemistry. 19 (11): 641–7. doi:10.1177/19.11.641. PMID 4107745.