Properties
Hydrogen sulfide is slightly heavier than air; a mixture of H2S and air is explosive. Hydrogen sulfide and oxygen burn with a blue flame to form sulfur dioxide (SO2) 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− (pKa = 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 pKa > 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 is put into contact with concentrated nitric acid, it explodes.
Hydrogen sulfide reacts with alcohols to form thiols.
Read more about this topic: Hydrogen Sulfide
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