Hydrosulfuric Acid: Hydrogen sulfide is a chemical compound with the formula H2S and having a PH of 4.5. It is a colorless chalcogen hydride gas with the characteristic foul smell of rotten eggs. It is toxic, corrosive, and flammable. Hydrogen sulfide is generally built from the microbial disintegration of organic matter in the deficiency of oxygen gas, such as in swamps and sewers; this mechanism is commonly known as anaerobic digestion which is done by sulfate-reducing microorganisms. H2S also appears in volcanic gases, natural gas, and in some origins of well water.

The human body produces small amounts of H2S and uses it as a beckoning molecule. Swedish chemist Carl Wilhelm Scheele is credited with having determined the chemical composition of hydrogen sulfide in 1777. The British English spelling of this compound is hydrogen sulfide, but this spelling is not recommended by the International Union of Pure and Applied Chemistry (IUPAC) or the Royal Society of Chemistry.

Hydrosulfuric Acid Formula & Structure

The structure of hydrosulfuric acid is identical to that of water. However, sulfur is less electronegative than oxygen. Therefore, hydrogen sulfide is less polar than water. Because of this, comparably weaker intermolecular forces remain in H2S and the melting and boiling point are way smaller than in water.

Hydrosulfuric Acid Formula And Structure
Hydrosulfuric Acid Formula And Structure


Hydrogen sulfide is formed out of two hydrogen atoms and one sulfur atom. Hydrogen sulfide is denser than ordinary air, and when burned with oxygen it produces a blue flame. The burning of hydrogen sulfide produces water and sulfur dioxide. Hydrogen sulfide acts as a reducing agent, a compound or element that sheds an electron to a diverse chemical during the course of a redox chemical reaction.

When combined with catalysts or at high temperatures, hydrogen sulfide, and sulfur dioxide will react with one another to form water and sulfur. This reaction is utilized to adapt hydrogen sulfide in industrial operations. Hydrogen sulfide behaviors as a weak acid, and it is water-soluble, though not heavily water-soluble. When combined with air, the solution will oxidize and create sulfur, which isn’t water-soluble.

Although hydrogen sulfide has a structure comparable to water, sulfur has nowhere near the level of electronegativity than oxygen does, meaning that hydrogen sulfide is much less polar than water. Due to hydrogen sulfide’s less polar nature, the melting and boiling points for hydrogen sulfide are substantially lower than water’s boiling point. Hydrogen sulfide boils at -60.7°C while the water boils at 100°C.

Pure hydrogen sulfide is colorless and so are solutions involving it. Hydrogen sulfide forms metal sulfides when it acts with metal ions. These metal sulfides are usually dark in coloration and are water-insoluble. If metal sulfides are treated with a strong acid they free up hydrogen sulfide.

When pressurized above 90 gigapascals the molecules of hydrogen sulfide are capable to conduct electricity. High-pressure hydrogen sulfide exhibits superconductivity when it is cooled down below a critical temperature. As pressure increases, the critical temperature also increases. The critical temperature for hydrogen sulfide is elsewhere between 23K at 100 gigapascals and 150 K at 200 gigapascals.

Hydrogen sulfide’s odor is so potent that it can be detected at levels of around 2 ppb. As an associating, a concentration of 20 ppb would be 1 mL of the gas evenly distributed in a 100 seat college lecture hall.

We can very easily obtain hydrosulfuric acid by its separation from the sour gas, which is natural gas that has a high content of H2S. We can also produce it by the process of treating the hydrogen gas with the molten elemental sulfur at a temperature of about 450 °C. The hydrocarbons are capable of serving as a source of hydrogen in this particular process.

A standard lab preparation is below to treat the ferrous sulfide with a strong acid in a Kip generator:

FeS + 2 HCl → FeCl2 + H2S

For the use in qualitative inorganic analysis, thioacetamide is used to produce the H2S:

CH3C(S)NH2 + H2O → CH3C(O)NH2 + H2S

Multiple metals and non-metal sulfides, such as the aluminum sulfide, phosphorus pentasulfide, and silicon disulfide liberate the hydrogen sulfide upon exposure to the water (H2O):

6 H2O + Al2S3 → 3 H2S + 2 Al(OH)3

We can also easily produce this gas by the process of heating the sulfur with the solid organic compounds also and by reducing the sulfurized organic compounds with hydrogen.


Small amounts of hydrogen sulfide occur in crude petroleum, but natural gas has the capability to contain up to 30 percent. Moreover, the volcanoes and some hot springs, as well as various cold springs, also emit some H2S, where it usually arises through the process of hydrolysis of the sulfide minerals, i.e. MS + H2O → MO + H2S.

Hydrosulfuric Acid PH

pH freshly prepared water solution 4.5

Hydrosulfuric Acid Properties

Name: Hydrosulfuric Acid
Also Known as: Hydrogen Sulfide and Sulfane
Appearance: Colourless Gas
Chemical Formula: H2S
Melting Point: -82 Degrees Celsius
Boiling Point: -60 Degrees Celsius
Molar Mass: 34.0809
Distinguishing Factor: Smells like rotten eggs

The hydrosulfuric acid is lightly denser than the air, a mixture of H2S with the air can be explosive. As well, the hydrogen sulfide gets ignited in the oxygen with the help of a flame that is blue in color to generate sulfur dioxide i.e. SO2 and water (H2O). Basically, the hydrogen sulfide carries out as a reducing agent, specifically in the existence of the base and this forms SH−. At high-level temperatures or in the existence of the catalysts, the sulfur dioxide conclusions in a reaction with the hydrogen sulfide to form elementary sulfur and water at the same time.

H2S is a colorless gas at room temperature. Its melting point is -82 ̊C (-115.6 ̊F), boiling point -60 ̊C (-76 ̊F), density 0.00136 g/cm3. H2S has an odor of rotten eggs. It is toxic, corrosive, and flammable.

pH freshly prepared water soln: 4.5

Important Reactions

  • FeS + 2HCl = FeCl2 + H2S
  • H2SO4 + 8HI = H2S + 4I2 + 4H2O
  • Co(NO3)2 + H2S = CoS + 2HNO3
  • H2S + 4Na2O2 + 2H2O = Na2SO4 + 6NaOH
  • H2S + 2AgNO3 = Ag2S + 2HNO3
  • ZnS + 2HCl = ZnCl2 + H2S
  • H2S + CuCl2 = CuS + 2HCl
  • H2S + 2KOH = 2H2O + K2S
  • H2S + HgCl2 = HgS + 2HCl
  • Na2S + 2HCl = 2NaCl + H2S


Hydrogen sulfide is a highly toxic and flammable gas in nature with a flammable range of 43 to 46 percent. Because of being heavier than the air, it tends to accumulate at the bottom of the poorly ventilated spaces available easily. Although it is very pungent at first, it quickly deadens the sense of smell that smells like rotten eggs. Therefore, the victims should be aware of its presence until it is too late for being safe with it.