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|Section2= |Section3= |Section4= |Section5= |Section6= }} Hydrogen sulfide is the chemical compound with the formula . It is a colorless gas with the characteristic foul odor of rotten eggs; it is heavier than air, very poisonous, corrosive, flammable, and explosive. Hydrogen sulfide often results from the bacterial breakdown of organic matter in the absence of oxygen gas, such as in swamps and sewers; this process is commonly known as anaerobic digestion. also occurs in volcanic gases, natural gas, and in some sources of well water. It is also present in natural halite type rock salts, most notably in Himalayan Black Salt, which is mostly harvested from the mineral-rich "Salt Range" mountains of Pakistan. The human body produces small amounts of and uses it as a signaling molecule. Dissolved in water, hydrogen sulfide is known as hydrosulfuric acid or sulfhydric acid, a weak acid. Swedish chemist Carl Wilhelm Scheele is credited with having discovered hydrogen sulfide in 1777. The British English spelling of this compound is ''hydrogen sulphide'', but this spelling is not recommended by the International Union of Pure and Applied Chemistry or the Royal Society of Chemistry. In 2015, hydrogen sulfide under extremely high pressure (around 150 gigapascals) was found to undergo superconducting transition near 203K (-70 °C), the highest temperature superconductor known to date. ==Properties== Hydrogen sulfide is slightly heavier than air; a mixture of and air can be explosive. Hydrogen sulfide and oxygen burn with a blue flame to form sulfur dioxide () and water. In general, hydrogen sulfide acts as a reducing agent. At high temperature or in the presence of catalysts, sulfur dioxide can be made to react with hydrogen sulfide to form elemental sulfur and water. This is exploited in the Claus process, the main way to convert hydrogen sulfide into elemental sulfur. Hydrogen sulfide is slightly soluble in water and acts as a weak acid, giving the hydrosulfide ion HS− (p''K''a = 6.9 in 0.01-0.1 mol/litre solutions at 18 °C). A solution of hydrogen sulfide in water, known as ''sulfhydric acid'' or ''hydrosulfuric acid'', is initially clear but over time turns cloudy. This is due to the slow reaction of hydrogen sulfide with the oxygen dissolved in water, yielding elemental sulfur, which precipitates out. The sulfide dianion S2− exists only in strongly alkaline aqueous solutions; it is exceptionally basic with a p''K''a > 14. Hydrogen sulfide reacts with metal ions to form metal sulfides, which may be considered the salts of hydrogen sulfide. Some ores are sulfides. Metal sulfides often have a dark color. Lead(II) acetate paper is used to detect hydrogen sulfide because it turns grey in the presence of the gas as lead(II) sulfide is produced. Reacting metal sulfides with strong acid liberates hydrogen sulfide. If gaseous hydrogen sulfide (a strong reducing agent) is put into contact with concentrated nitric acid (a strong oxidizer), it reacts explosively to give NOx, SOx, nitrogen, and water. Hydrogen sulfide reacts with alcohols to form thiols, an important class of organosulfur compounds. At pressures above 90 GPa (Gigapascal), hydrogen sulfide becomes a metallic conductor of electricity. When cooled below a critical temperature this high-pressure phase exhibits superconductivity. The critical temperature increases with pressure, ranging from 23 K at 100 GPa to 150 K at 200 GPa. If hydrogen sulfide is pressurized at higher temperatures, then cooled, the critical temperature reaches 203 K, (-70 °C) the highest accepted superconducting critical temperature as of 2015.〔 By substituting a small part of sulfur with phosphorus and using even higher pressures, it has been predicted that it may be possible to raise the critical temperature to above 0 °C and achieve room-temperature superconductivity.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Hydrogen sulfide」の詳細全文を読む スポンサード リンク
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