Hydrogen sulfide

Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is poisonous, corrosive, and flammable, with trace amounts in ambient atmosphere having a characteristic foul odor of rotten eggs. The underground mine gas term for foul-smelling hydrogen sulfide-rich gas mixtures is stinkdamp. Swedish chemist Carl Wilhelm Scheele is credited with having discovered the chemical composition of purified hydrogen sulfide in 1777. The British English spelling of this compound is hydrogen sulphide, a spelling no longer recommended by the Royal Society of Chemistry or the International Union of Pure and Applied Chemistry. Hydrogen sulfide is toxic to humans and most other animals by inhibiting cellular respiration in a manner similar to hydrogen cyanide. When it is inhaled or its salts are ingested in high amounts, damage to organs occurs rapidly with symptoms ranging from breathing difficulties to convulsions and death. Despite this, the human body produces small amounts of this sulfide and its mineral salts, and uses it as a signalling molecule. Hydrogen sulfide is often produced from the microbial breakdown of organic matter in the absence of oxygen, such as in swamps and sewers; this process is commonly known as anaerobic digestion, which is done by sulfate-reducing microorganisms. It also occurs in volcanic gases, natural gas deposits, and sometimes in well-drawn water. Hydrogen sulfide is slightly denser than air. A mixture of and air can be explosive. In general, hydrogen sulfide acts as a reducing agent, although in the presence of a base, it can act as an acid by donating a proton and forming . Hydrogen sulfide burns in oxygen with a blue flame to form sulfur dioxide () and water: If an excess of oxygen is present, sulfur trioxide () is formed, which quickly hydrates to sulfuric acid: At high temperatures or in the presence of catalysts, sulfur dioxide reacts with hydrogen sulfide to form elemental sulfur and water. This reaction is exploited in the Claus process, an important industrial method to dispose of hydrogen sulfide.