Hydrogen sulphide is a very deadly and combustible gas that smells like rotten eggs. The lack of oxygen, such as in swamps and sewers, is caused by the bacterial degradation of organic materials. Volcanic gases, natural gas, and some well waters all contain it. Hydrogen sulphide is denoted by the formula H2S. It is a signalling molecule that the human body produces at minute levels. Hydrogen sulphide is used to make a variety of organosulfur compounds.

When hydrogen sulphide reacts with alkali metal bases, it forms alkali hydrosulfide such as sodium hydrosulfide and sodium sulphide, which are utilised to degrade biopolymers. For well over a century, the properties of hydrogen sulphide were important in analytical chemistry, particularly in the qualitative inorganic analysis of metal ions. Mineral powders are frequently treated with hydrogen sulphide to improve separation in the flotation purification of metal ores.

Physical Properties of Hydrogen Sulphide

Let’s take a look at the properties of hydrogen sulphide.

• Visibility: H2S is colourless and has a reflective ratio close to air, making it extremely difficult to detect with our eyes.
• Boiling point: It is usually found in a gaseous state, with a boiling point of -60.4°C in water.
• Density: With a density of 1.1363 relative to the air, it is heavier and denser than air. As a result, it is more likely to be found in low-lying places with little to no ventilation. It can, however, soar in the air if the conditions are favourable.
• Flammable: When subjected to a relatively cool heat source of 232°C, H2S is highly explosive and only takes a concentration of 4% to cause a flash fire.
• Explosive: In the presence of high nitric acid, H2S is explosive and reactive.
• Dissipation in water: H2S is a gas that is soluble in water and a variety of other liquids. When it dissolves in water, it produces hydro sulfuric acid, which can irritate the eyes. H2S-contaminated water is usually clear, but it might turn hazy as the sulphur precipitates out.
• Corrosiveness: This is one of the hydrogen sulphide examples as they are corroded by it because it generates metal sulphides.

• Smell: It smells like rotten eggs in low quantities, although the fragrance varies depending on the amounts. In doses of 100 ppm, the olfactory receptors in the nose become paralysed. In low doses, these receptors become exhausted quickly and are no longer an effective H2S detector.

Chemical Properties of Hydrogen Sulphide

Here are the chemical properties of Hydrogen Sulphide.

• Burning: It is a flammable gas that emits a pale blue flame. It opposes combustion in any form. It burns to produce sulphur and water when there is a shortage of air or oxygen.

• Disintegration: It decomposes when heated, releasing hydrogen and sulphur. Decomposition begins at 310°C and finishes at 1700°C.

• Acidic properties: The gas is acidic and causes moist blue litmus paper to turn red. Because of the H₃O⁺ ions, the aqueous solution of H2S is acidic.

  • It reacts with caustic alkalis like NaOH to produce two salts. 
  • It cannot break down carbonates because it is a weaker acid than carbonic acid (H₂CO₃).
  • Ammonium sulphide is generated when ammonia is treated with NH₃.
  • When it reacts with metals like Ag or Sn, it produces metal sulphide and hydrogen gas.
• Reducing agent: Due to the ease with which hydrogen sulphide decomposes to give hydrogen and sulphur, it is a powerful reducing agent. The following are some of the most important hydrogen sulphide reduction reactions:
  • It reduces halogens to halogen acids.
  • It converts sulphur dioxide (SO₂) to sulphur.
  • Ferric sulphate [Fe₂(SO₄)₃] is converted to ferrous sulphate.
  • It converts H₂SO₄ to SO₂.
  • NO2 is produced due to HNO3 action.
  • It brightens the pink colour of the KMnO4 solution.
  • Acidified K2Cr2O7 solution is turned green.

• Precipitation reactions: It interacts with metallic salt solutions to generate coloured insoluble sulphide precipitates. In this example, there are two scenarios:

  • Precipitation reactions in an acid medium: In the presence of dilute HCl, hydrogen sulphide combines with metal salts such as Cu, Bi, Cd, As, and others to form a colourful precipitate of their sulphides.

  • Alkaline medium precipitation reactions: In an ammoniacal media (NH4OH), hydrogen sulphide combines with metal salts such as Co, Ni, and Zn to form coloured sulphides.

Conclusion

H2S, or hydrogen sulphide, is a colourless, highly poisonous, and combustible gas with a rotten egg stench. It is used to make chemicals, in metallurgy, and as an analytical reagent. Because it is heavier than air, it collects at the bottom of poorly ventilated spaces. Although at first intense, it quickly dulls the sense of smell. 

Understanding the characteristics of hydrogen sulphide is an important part of the H2S Alive training. Knowing these hydrogen sulphide examples can help you stay safe when working in the natural gas or petroleum industries.