hydrogen selenide hydrogen selenide hydrogen selenide is an inorganic compound with the formula h2se. this hydrogen chalcogenide is the simplest and most commonly encountered hydride of selenium. h2se is a colorless, flammable gas under standard conditions. it is the most toxic selenium compound with an exposure limit of 0.05 ppm over an 8-hour period. even at extremely low concentrations, this compound has a very irritating smell resembling that of decayed horseradish or 'leaking gas', but smells of rotten eggs at higher concentrations. hydrogen selenide structural diagram of the hydrogen selenide molecule space-filling model of the hydrogen selenide molecule names iupac name hydrogen selenide other names hydroselenic acidselaneselenium hydride identifiers cas number 7783-07-5 y 3d model (jsmol) interactive image chebi chebi:16503 y chemspider 518 y echa infocard 100.029.071 ec number 231-978-9 kegg c01528 y pubchem cid 533 rtecs number x1050000 unii v91p54kpam y un number 2202 comptox dashboard (epa) dtxsid20872822 inchi inchi=1s/h2se/h1h2 ykey: spvxkvoxsxtjoy-uhfffaoysa-n yinchi=1/h2se/h1h2key: spvxkvoxsxtjoy-uhfffaoyaf smiles properties chemical formula h2se molar mass 80.98 g/mol appearance colorless gas odor decayed horseradish density 3.553 g/dm3 melting point −65.73 °c (−86.31 °f; 207.42 k) boiling point −41.25 °c (−42.25 °f; 231.90 k) solubility in water 0.70 g/100 ml solubility soluble in cs2, phosgene vapor pressure 9.5 atm (21°c) acidity (pka) 3.89 conjugate acid selenonium conjugate base selenide structure molecular shape bent hazards occupational safety and health (ohs/osh): main hazards extremely toxic and flammable ghs labelling: pictograms signal word danger hazard statements h220, h280, h330, h410 precautionary statements p210, p260, p271, p273, p284, p304+p340, p310, p320, p377, p381, p391, p403, p403+p233, p405, p410+p403, p501 nfpa 704 (fire diamond) 4 4 0 flash point flammable gas lethal dose or concentration (ld, lc): lclo (lowest published) 0.3 ppm (guinea pig, 8 hr)5.9 ppm (rat, 1 hr) niosh (us health exposure limits): pel (permissible) twa 0.05 ppm (0.2 mg/m3) rel (recommended) twa 0.05 ppm (0.2 mg/m3) idlh (immediate danger) 1 ppm safety data sheet (sds) icsc 0284 related compounds other anions h2oh2sh2teh2po other cations na2seag2se related compounds arsine except where otherwise noted, data are given for materials in their standard state (at 25 °c , 100 kpa). n verify (what is yn ?) infobox references structure and properties h2se adopts a bent structure with a h−se−h bond angle of 91°. consistent with this structure, three ir-active vibrational bands are observed: 2358, 2345, and 1034 cm−1. the properties of h2s and h2se are similar, although the selenide is more acidic with pka = 3.89 and the second pka = 11, or 15.05 ± 0.02 at 25 °c. preparation industrially, it is produced by treating elemental selenium at t > 300 °c with hydrogen gas. a number of routes to h2se have been reported, which are suitable for both large and small scale preparations. in the laboratory, h2se is usually prepared by the action of water on al2se3, concomitant with formation of hydrated alumina. a related reaction involves the acid hydrolysis of fese. al2se3 + 6 h2o ⇌ 2 al(oh)3 + 3 h2se h2se can also be prepared by means of different methods based on the in situ generation in aqueous solution using boron hydride, marsh test and devarda's alloy. according to the sonoda method, h2se is generated from the reaction of h2o and co on se in the presence of et3n. h2se can be purchased in cylinders. reactions elemental selenium can be recovered from h2se through a reaction with aqueous sulfur dioxide (so2). 2 h2se + so2 ⇌ 2 h2o + 2 se + s its decomposition is used to prepare the highly pure element. applications h2se is commonly used in the synthesis of se-containing compounds. it adds across alkenes. illustrative is the synthesis of selenoureas from cyanamides: h2se gas is used to dope semiconductors with selenium. safety hydrogen selenide is hazardous, being the most toxic selenium compound and far more toxic than its congener hydrogen sulfide. the threshold limit value is 0.05 ppm. the gas acts as an irritant at concentrations higher than 0.3 ppm, which is the main warning sign of exposure; below 1 ppm, this is "insufficient to prevent exposure", while at 1.5 ppm the irritation is "intolerable". exposure at high concentrations, even for less than a minute, causes the gas to attack the eyes and mucous membranes; this causes cold-like symptoms for at least a few days afterwards. in germany, the limit in drinking water is 0.008 mg/l, and the us epa recommends a maximum contamination of 0.01 mg/l. despite being highly toxic, no human fatalities have yet been reported. it is suspected that this is due to the gas' tendency to oxidise to form red selenium in mucous membranes; elemental selenium is less toxic than selenides are.