Phosphorous acid - wikipedia Phosphorous acid `` Phosphonic acid '' redirects here. For Phosphonic acids, see Phosphonate. Not to be confused with Phosphoric acid. Phosphorous acid Names IUPAC name phosphonic acid Other names Dihydroxyphosphine oxide Dihydroxy ( oxo ) - λ - phosphane Dihydroxy - λ - phosphanone Orthophosphorous acid Oxo - λ - phosphanediol Oxo - λ - phosphonous acid Identifiers CAS Number 13598 - 36 - 2 3D model ( JSmol ) Interactive image ChEBI CHEBI : 44976 ChemSpider 10449259 10459438 ( O ) ECHA InfoCard 100.033. 682 KEGG C06701 RTECS number SZ6400000 UNII 35V6A8JW8E InChI InChI = 1S / H3O3P / c1 - 4 ( 2 ) 3 / h4H, ( H2, 1, 2, 3 ) Key : ABLZXFCXXLZCGV - UHFFFAOYSA - N InChI = 1 / H3O3P / c1 - 4 ( 2 ) 3 / h4H, ( H2, 1, 2, 3 ) Key : ABLZXFCXXLZCGV - UHFFFAOYAF SMILES OP ( = O ) O Properties Chemical formula H PO Molar mass 81.99 g / mol Appearance white solid deliquescent Density 1.651 g / cm ( 21 ° C ) Melting point 73.6 ° C ( 164.5 ° F ; 346.8 K ) Boiling point 200 ° C ( 392 ° F ; 473 K ) ( decomposes ) Solubility in water 310 g / 100 mL Solubility soluble in alcohol Acidity ( pK ) 1.1, 6.7 Magnetic susceptibility ( χ ) − 42.5 10 cm / mol Structure Molecular shape pseudo-tetrahedral Hazards Main hazards skin irritant Safety data sheet http://www.sigmaaldrich.com/MSDS/ R - phrases ( outdated ) 22 - 35 S - phrases ( outdated ) 26 - 36 / 37 / 39 - 45 NFPA 704 0 Related compounds Related compounds H PO ( i.e., PO ( OH ) ) H PO ( i.e., H PO ( OH ) ) Except where otherwise noted, data are given for materials in their standard state ( at 25 ° C ( 77 ° F ), 100 kPa ). N verify ( what is ? ) Infobox references Phosphorous acid is the compound described by the formula H PO. This acid is diprotic ( readily ionizes two protons ), not triprotic as might be suggested by this formula. Phosphorous acid is an intermediate in the preparation of other phosphorus compounds. Contents 1 Nomenclature and tautomerism 2 Preparation 3 Reactions 3.1 Acid -- base properties 3.2 Disproportionation 3.3 Reductions of metal ions 3.4 As a ligand 4 Uses 5 Organic derivatives 6 References 7 Further reading Nomenclature and tautomerism H PO is more clearly described with the structural formula HPO ( OH ). In the solid state, HP ( O ) ( OH ) is tetrahedral with one shorter P =O bond of 148 pm and two longer P -- O ( H ) bonds of 154 pm. This species exists in equilibrium with an extremely minor tautomer P ( OH ). IUPAC recommends that the latter be called phosphorous acid, whereas the dihydroxy form is called phosphonic acid. Only the reduced phosphorus compounds are spelled with an `` ous '' ending. Other important oxyacids of phosphorus are phosphoric acid ( H PO ) and hypophosphorous acid ( H PO ). The reduced phosphorus acids are subject to similar tautomerism involving shifts of H between O and P. Preparation HPO ( OH ) is the product of the hydrolysis of its acid anhydride : P O + 6 H O → 4 HPO ( OH ) ( An analogous relationship connects H PO and P O ). On an industrial scale, the acid is prepared by hydrolysis of phosphorus trichloride with water or steam : PCl + 3 H O → HPO ( OH ) + 3 HCl Potassium phosphite is also a convenient precursor to phosphorous acid : K HPO + 2 HCl → 2 KCl + H PO In practice aqueous potassium phosphite is treated with excess hydrochloric acid. By concentrating the solution and precipitations with alcohols, the pure acid can be separated from the salt. Reactions Acid -- base properties Phosphorous acid is a strong acid with ap K in the range 1.26 -- 1.3. HP ( O ) ( OH ) → HP ( O ) ( OH ) + H pK = 1.3 It is a diprotic acid, the hydrogenphosphite ion, HP ( O ) ( OH ) is a moderately strong acid : HP ( O ) ( OH ) → HPO + H pK = 6.7 The conjugate base HP ( O ) ( OH ) is called hydrogen phosphite, and the second conjugate base, HPO, is the phosphite ion. ( Note that the IUPAC recommendations are hydrogen phosphonate and phosphonate respectively ). The hydrogen atom bonded directly to the phosphorus atom is not readily ionizable. Chemistry examinations often test students ' appreciation of the fact that not all three hydrogen atoms are acidic under aqueous conditions, in contrast with H PO. Disproportionation On heating at 200 ° C, phosphorous acid disproportionates to phosphoric acid and phosphine : 4 H PO → 3 H PO + PH This reaction is used for laboratory - scale preparations of PH. Reductions of metal ions Both phosphorous acid and its deprotonated forms are good reducing agents, although not necessarily quick to react. They are oxidized to phosphoric acid or its salts. It reduces solutions of noble metal cations to the metals. When phosphorous acid is treated with a cold solution of mercuric chloride, a white precipitate of mercurous chloride forms : H PO + 2 HgCl + H O → Hg Cl + H PO + 2 HCl Mercurous chloride is reduced further by phosphorous acid to mercury on heating or on standing : H PO + Hg Cl + H O → 2 Hg + H PO + 2 HCl As a ligand Upon treatment with metals of d6 configuration, phosphorous acid is known to coordinate as the otherwise rare P ( OH ) tautomer. Examples include Mo ( CO ) ( P ( OH ) ) and ( Ru ( NH ) ( H O ) ( P ( OH ) ) ). Uses The most important use of phosphorous acid ( phosphonic acid ) is the production of basic lead phosphite, which is a stabilizer in PVC and related chlorinated polymers. Phosphites have shown effectiveness in controlling a variety of plant diseases, in particular, treatment using either trunk injection or foliar containing phosphorous acid salts is indicated in response to infections by phytophthora and pythium - type plant pathogens ( both within class oomycetes, known as water molds ), such as dieback / root rot and downy mildew. Anti-microbial products containing salts of phosphorous acid are marketed in Australia as ' Yates Anti-Rot ' ; and in the United States of America, for example, aluminum salts of the monoethyl ester of phosphorous acid ( known generically as ' Fosetyl - Al ' ) are sold under the trade name ' Aliette ' and potassium salts of phosphorous acid ( known generically as potassium phosphite ) are sold under the trade name ProPhyt. Phosphorous acid and its salts, unlike phosphoric acid, are somewhat toxic and should be handled carefully. Organic derivatives The IUPAC ( mostly organic ) name is phosphonic acid. This nomenclature is commonly reserved for substituted derivatives, that is, organic group bonded to phosphorus, not simply an ester. For example, ( CH ) PO ( OH ) is `` methylphosphonic acid '', which may of course form `` methyl phosphonate '' esters. References Jump up ^ `` MSDS - 215112 ''. www.sigmaaldrich.com. Retrieved 12 April 2018. Jump up ^ International Union of Pure and Applied Chemistry ( 2005 ). Nomenclature of Inorganic Chemistry ( IUPAC Recommendations 2005 ). Cambridge ( UK ) : RSC -- IUPAC. ISBN 0 - 85404 - 438 - 8. Electronic version... ^ Jump up to : Betterman, G. ; Krause, W. ; Riess, G. ; Hofmann, T. `` Phosphorus Compounds, Inorganic '' Ullmann 's Encyclopedia of Industrial Chemistry, 2005, Wiley - VCH, Weinheim. doi : 10.1002 / 14356007. a19_527. Jump up ^ Larson, John W. ; Pippin, Margaret ( 1989 ). `` Thermodynamics of ionization of hypophosphorous and phosphorous acids. Substituent effects on second row oxy acids ''. Polyhedron. 8 : 527 -- 530. doi : 10.1016 / S0277 - 5387 ( 00 ) 80751 - 2. Jump up ^ CRC Handbook of Chemistry and Physics ( 87th ed. ). p. 8 -- 42. Jump up ^ Novosad, Josef ( 1994 ). Encyclopedia of Inorganic Chemistry. John Wiley and Sons. ISBN 0 - 471 - 93620 - 0. Jump up ^ Gokhale, S.D. ; Jolly, W.L. ( 1967 ). `` Phosphine ''. Inorganic Syntheses. 9 : 56 -- 58. doi : 10.1002 / 9780470132401. ch17. Jump up ^ Sernaglia, R.L. ; Franco, D.W. ( 2005 ). `` The ruthenium ( II ) center and the phosphite - phosphonate tautomeric equilibrium ''. Inorg. Chem. 28 : 3485 -- 3489. doi : 10.1021 / ic00317a018. CS1 maint : Uses authors parameter ( link ) Jump up ^ Xi, Chanjuan ; Liu, Yuzhou ; Lai, Chunbo ; Zhou, Lishan ( 2004 ). `` Synthesis of molybdenum complex with novel P ( OH ) ligand based on the one - pot reaction of Mo ( CO ) with HP ( O ) ( OEt ) and water ''. Inorganic Chemistry Communications. 7 ( 11 ) : 1202. doi : 10.1016 / j. inoche. 2004.09. 012. Jump up ^ `` Organic Labs. Phosphites with approved fungicide label in the European Union countries such as France sold under the trade name ' LBG ' and in the United States of America sold under the trade name ' ProPhyt '. The Product label for ' Exel LG, ' Retrieved April 9, 2007 ''. organiclabs.com. Retrieved 12 April 2018. Jump up ^ `` Yates, a Division of Orica Australia Pty Ltd. `` MSDS ( ' Yates Anti Rot Phosacid Systemic Fungicide ' ). '' Version 1. SH&E Shared Services, Orica. Homebush, NSW ( Australia ) : April 4, 2005 ( retrieved from www.orica.com April 9, 2007 ) '' ( PDF ). orica.com. Retrieved 12 April 2018. Jump up ^ ( ( s : Image : Fosetyl - al red - facts 1994. pdf US EPA. `` Fosetyl - Al ( Aliette ) : Reregistration Eligibility Dh as Franceecision ( RED ) Fact Sheet. '' Office of Pesticide Programs, US EPA. Washington, DC ( USA ) : 1994 ( retrieved from www.epa.gov April 9, 2007 ). ) ) Further reading Holleman, A.F. ; Wiberg, E. ( 2001 ). Inorganic Chemistry. San Diego : Academic Press. ISBN 0 - 12 - 352651 - 5. Corbridge., D.E.C. Phosphorus : An Outline of its Chemistry, Biochemistry, and Technology ( 5th ed. ). Amsterdam : Elsevier. ISBN 0 - 444 - 89307 - 5. Lee, J.D. Concise Inorganic Chemistry. Oxford University Press. ISBN 978 - 81 - 265 - 1554 - 7. Hydrogen compounds H AsO H AsO HAt HSO F HBF HBr HBrO HBrO HBrO HBrO HCl HClO HClO HClO HClO HCN HCNO H CrO / H Cr O H CO H CS HF HFΟ HI HIO HIO HIO HIO HMnO H MoO HNC NaHCO HNCO HNO HNO HNO H N O HNO S H NSO H O H O H O H PO H PO H PO H P O H P O H PtCl H Se H SeO H SeO H SiO H SiF HSCN HNSC H SO H SO H SO H S O H S O H S O H S O CF SO H H Te H TeO H TeO H TiO H Po HCo ( CO ) GND : 4519764 - 7 Retrieved from `` https://en.wikipedia.org/w/index.php?title=Phosphorous_acid&oldid=850870072 '' Categories : Hydrogen compounds Phosphorus oxoacids Phosphonates Phosphonic acids Hidden categories : CS1 maint : Uses authors parameter Chemical articles with multiple compound IDs Multiple chemicals in an infobox that need indexing Chemicals without a PubChem CID ECHA InfoCard ID from Wikidata Articles with changed FDA identifier Chembox having DSD data Articles containing unverified chemical infoboxes Wikipedia articles with GND identifiers Talk Contents About Wikipedia تۆرکجه Bosanski Català Čeština Deutsch Español فارسی Français 한국어 हिन्दी Hrvatski Italiano Bahasa Melayu Nederlands 日本 語 Polski Português Română Русский Simple English Slovenčina Српски / srpski Srpskohrvatski / српскохрватски Suomi Svenska Українська Tiếng Việt 中文 20 more Edit links This page was last edited on 18 July 2018, at 14 : 07 ( UTC ). 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Question: what is the systematic name for aqueous h3po3
Answer: Phosphorous acid