Introduction:

Sulphur in oxoacids has a tetrahedral shape in relation to oxygen. These oxoacids usually feature at least one S=O bond and one S-OH bond. These oxoacids also include terminal peroxide groups, terminal S=S, and terminal and bridging oxygen atoms. Let’s have a look at some of the most well-known oxoacids and their characteristics.

Sulphuric acid (H2SO4)

One of the most utilised sulphur oxoacids is sulphuric acid. It’s a diprotic acid of some kind – It ionises to give two protons. In sulphuric acid, one sulphur atom is attached to two hydroxyl groups, while the other two oxygen atoms establish pi connections with the sulphur atom. Sulphuric acid has a tetrahedral structure as a consequence.

Because the sulphur oxygen connection (S=O) is shorter than the bond length of S-OH, the oxygen atoms reject the OH groups. Consequently, the O=S=O bond has a higher bond angle than the HO-S-OH bond. In the industry, the contact process is used to produce it.

Preparation:

H2SO4 is prepared from Contact’s process by the following steps:

• Step I: Preparation of sulphur dioxide.

S + O2 —> SO2 (Sulphur dioxide)

• Step II: Preparation of sulphur trioxide.

SO2 + O2 —> SO3 (Sulphur trioxide)

• Step III: Reaction of sulphur trioxide with concentrated Sulphuric acid.

SO3 + H2SO4 —> H2S2O7 (Oleum)

• Step IV: Diluting the oleum.

H2S2O7 + H2O —> H2SO4(dilute) (Sulphuric Acid)

• This sulphuric acid formed is 99% pure.

The Lead Chamber process can also prepare Sulphuric acid.

Physical Properties:

• Sulphuric acid is a viscous, colourless, and oily fluid with a thick consistency.
• At 298K, it has a specific gravity of 1.84.
• The acid’s boiling point is 611K. Because of hydrogen bonding, this molecule has a higher boiling point and a thicker consistency.
• This powerful chemical forcefully combines with water, creating significant heat. As a result, you should never mix H2SO4 with water. Instead, you should slowly add the acid to the water while swirling the mixture thoroughly.

Chemical Properties

• Acidic Property

Sulphuric acid is a dibasic acid with a high pH. Besides, it has diprotic properties and ionises twice in an aqueous solution.

Sulphuric acid, as an acid, interacts with the majority of bases to produce the corresponding sulphate. For example, when copper(II) oxide reacts with Sulphuric acid, it produces copper(II) sulphate and water.

CuO(s) + H2SO4(aq) → CuSO4(aq) + H2O(l)

• Dehydrating Property

Sulphuric acid in concentrated form is a particularly effective dehydrating agent. This chemical is used to dry a wide range of moist gases that do not react with the acid. It also removes water from natural mixtures such as starches.

• Reaction with Metals

Dilute Sulphuric acid reacts with many metals and produces hydrogen gas and salts. It also attacks reactive metals such as iron, aluminium, zinc, manganese, magnesium, and nickel.

Fe + H2SO4 → FeSO4 + H2

• Oxidising Property

It has high oxidising power, making it a powerful oxidising agent that can oxidise non-metals and metals. Later, it decomposes into sulphur dioxide.

Cu + 2H2SO4 → CuSO4 + SO2 + 2H2O

C + 2H2SO4 → CO2 + 2SO2 + 2H2O

S + 2H2O → 3SO2 + 2H2O

• Reaction with NaCl 

It produces hydrogen chloride gas and sodium bisulfate when it combines with sodium chloride.

NaCl + H2SO4 → NaHSO4 + HCl

Uses:

• Pharmaceuticals: It’s a solvent employed to synthesise a wide range of chemicals, including active medicinal components. Alkylating agents, extensively used in chemotherapy (treatment of cancer), are an active medicinal ingredient made from sulphuric acid.
• Fertilisers: Sulphuric acid is used in large quantities to produce phosphoric acid, used to generate phosphate fertilisers.
• Gasoline: Sulphuric acid can also be found in CEMS gas samples.
• Paper bleaching: Sulphuric acid is used in the pulp and paper industry to produce chlorine dioxide on-site. Chlorine dioxide is a vital bleaching agent in the ecologically friendly ECF chemical pulping process.
• Water treatment: Depending on the pH level of the water being treated, an acid or a base is injected in wastewater treatment. Neutralisation is the process of bringing the pH level of wastewater back to normal using Sulphuric acid or a base chemical.
• Cellulose fibres: Sulphuric acid also produces cellulose fibres like rayon.
• Colouring agents: As a colouring agent, it is employed to produce colours, medicines, and disinfectants.
• Regeneration of ion exchange resins: Strong acid cation resins are commonly regenerated with Sulphuric acid. It’s used to keep calcium sulphate precipitation under control.
• Electrophilic aromatic substitution: Electrophilic aromatic substitution of benzene with Sulphuric acid yields the corresponding sulfonic acids.

Sulphurous acid (H2SO3)

Sulphurous acid is a two-proton diprotic acid. One sulphur atom is connected to two hydroxyl groups in sulphurous acid, and one oxygen atom is bonded to the sulphur atom in a pie bond. Sulphur dioxide is dissolved in water to make this. Although no evidence of sulphurous acid in the solution has been found, the molecule can be separated in the gaseous state.

Physical Properties:

Chemical Properties:

According to Raman spectra, SO2 solutions shows that the intensities of the signals are consistent with the equilibrium:

SO2 + H2O ⇌ HSO−3 + H+

where Ka = 1.54×10−2 and pKa = 1.81.

Health Risks of Sulphurous Acid:

It’s a toxic, corrosive, and non-combustible material that should be avoided at all costs. When sulphur dioxide solution is inhaled, ingested, or comes into contact with the skin, it can cause severe harm and even death. When molten, it can cause severe burns to the eyes and skin. Avoid coming into contact with it on your skin. When exposed to this substance, it emits fumes that are corrosive, toxic, and irritating to the respiratory system.

Uses of Sulphurous Acid:

• In industry, sulphurous acid is utilised as an intermediary.
• As a reducing agent.
• As disinfectants.
• It is used in the production of paper products.

Peroxodisulphuric acid – H2S2O8

Sulphur in the +6 oxidation state is present in peroxo disulphuric acid. As a result, it is a powerful oxidiser and highly explosive. Marshall’s acid is the common name for it. It has one peroxide group, which acts as a link between the two sulphur atoms. Other than the peroxide group, each sulphur atom is coupled to one hydroxyl group (S-OH bond) and two oxygen atoms (S=O bond).

Physical Properties:

• The peroxy disulphuric acid is a colourless and odourless solid.
• It is water-soluble.
• It has eight hydrogen bond acceptors and one covalently bonded unit.
• It has a ten-atom heavy atom count.

Chemical Properties:

• Sulphuric acid and hydrogen peroxide are produced when peroxydisulphuric acid dissolves in water. The chemical equation for this is as follows:

H2S2O8 + 2H2O → H2O2 + 2H2SO4

• Silver oxide, nitric acid, and sulphuric acid are formed when peroxydisulphuric acid reacts with silver nitrate in an aqueous media. The chemical equation for this is as follows:

H2S2O8 + 2AgNO3 → Ag2O2 + 2H2SO4 + 2HNO3

Uses:

• Large-scale sulphuric acid synthesis was made possible by using peroxydisulphuric acid and its salts as a source of hydrogen peroxide.
• In photography, peroxydisulphuric acid can be employed as a hypo eliminator.
• It can also be employed as a strong oxidant, with the amount of oxidising agent used varying based on the reaction rate desired.

• Conclusion:

  Oxoacids are acids that have oxygen in them. Sulphur is known to create a variety of oxoacids, including H2SO4, H2SO3, and others. Chemical compounds with sulphur, oxygen, and hydrogen are called sulphur oxoacids. Of all the oxoacids of sulphur, Sulphuric acid is the most well-known and widely used in industry.