Phosphorous Acid

Also found in: Dictionary, Thesaurus, Medical, Wikipedia.
Related to Phosphorous Acid: hypophosphorous acid, metaphosphoric acid

phosphorous acid

[′fäs·fə·rəs ′as·əd]
(inorganic chemistry)
H3PO3 Alcohol- and water-soluble deliquescent white or yellowish crystals; decomposes at 200°C; used as an analytical reagent and reducing agent.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Phosphorous Acid


H3PO3, a weak dibasic acid. Anhydrous phosphorous acid occurs as colorless hygroscopic crystals with a density of 1.65 g/cm3 and a melting point of 70.1°C. The dissociation constants at 18°C are K1 = 5.1 × 10–2 and K2 = 1.8 × 10–7. The solubility at 20°C is approximately 80 percent. When heated to 250°C, anhydrous phosphorous acid decomposes into phosphoric acid and phosphine; its aqueous solutions decompose at this temperature into phosphoric acid and hydrogen. Phosphorous acid is readily oxidized by such agents as halogens and the oxides of nitrogen. It is produced by dissolving P4O6 (P2O3) in cold water, by hydrolyzing PC13, and by reacting phosphites with sulfuric acid. Phosphorous acid and its salts are used as reducing agents.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
A 100% nickel coating without any phosphorous incorporation was obtained when the plating was carried out in the absence of [H.sub.3][P0.sub.3] indicating that phosphorous acid is indeed the only electrochemically active phosphorous species which acts as the phosphorous source in the present solution.
The concentrations of phosphorous acid and phosphoric acid in the solution were kept constant at 20 and 40 g/L, respectively.
This was done by preparing samples at current densities of 5 and 15 A [dm.sup.-2] with different concentrations of phosphorous acid (0-20 g/L) in the bath.
In other words, it is the concentration of the phosphorous acid in the plating bath that controls the phosphorous content of the Ni-P coating at a specific current density.
Phosphorous acid has a tendency to get oxidized to phosphoric acid thereby adversely affecting the co-deposition process.