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Hydrogen Sulfide Information

Hydrogen sulfide is a colorless, toxic and flammable gas. It has a characteristic offensive stench much like that of rotten eggs. It is a highly poisonous gas that can cause death if one part of the gas is present in 1000 parts of air. Hydrogen sulfide is often formed from the bacterial disintegration of organic matter and human and animal wastes in the absence of oxygen. It is found naturally in natural gases, crude petroleum, hot springs, volcanic gases and some well waters.

  1. Preparation

    • Hydrogen sulfide gas is generally prepared on the laboratory scale by the action of dilute hydrochloric acid or sulfuric acid on ferrous sulfide solution in a Kipp's apparatus. The gas is washed with water and collected over hot water. It is rather impure contaminated with hydrogen.

      Pure gas, free from hydrogen can be obtained by the action of hot concentrated hydrochloric acid on antimony sulfide solution (i.e. stibnite). Also, the purest gas may be prepared synthetically by passing a mixture of sulfur vapor and hydrogen over finely ground nickel at 450 degree C. Hydrogen sulfide is best purified by cooling with solid carbon dioxide when it liquefies and then distilling the liquid.

    Physical Properties

    • Hydrogen sulfide is hardly soluble in water, but highly soluble in carbon disulfide. There is a similarity between the structures of water and hydrogen sulfide. But, the electronegativity of hydrogen sulfide is less than oxygen; therefore it is not polar as much as water. Also, the melting and boiling point of hydrogen sulfide is much lower in comparison to water because of the weak intermolecular forces that exist in hydrogen sulfide.

    Chemical Properties

    • In aqueous solution, hydrogen sulfide forms a very weak dibasic acid called hydrosulfuric acid. Being a weak acid, hydrogen sulfide reacts with alkali hydroxide solutions to form sulphides and hydrosulphides. It is a flammable gas--in an excess of air, it combusts to form sulfur dioxide and water. If enough oxygen is not present, it burns to form elemental sulfur and water. Hydrogen sulfide is a good reducing agent because of the ease with which it decomposes into hydrogen and sulfur. It is oxidized to sulfur, sulfurous or sulfuric acid during the reduction process.

    Analytical Aspects

    • Hydrogen sulfide is detected by its characteristic odor, by its action on lead acetate paper which turns black and in alkaline solution, or by its action on sodium nitroprusside solution which turns violet. In aqueous solution, hydrogen sulfide is estimated by titration with a standard iodine solution.

    Uses

    • Hydrogen sulfide is the main ingredient in the production of sulfur, which is a commercially important element. Hydrogen sulfide has been using in qualitative analysis of metal ions for more than a century.

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