Sulphuric Acid is one of the most common mineral acids used in chemistry laboratories and chemical industry. It is also known by the name, oil of vitriol. Its basic composition comprises of three elements, namely sulphur, hydrogen and oxygen. It exists as a colourless, odourless, dense and oily liquid and is one of the most corrosive acids. The pH of 0.1 molar solution of sulphuric acid is 0.7 (which is strongly acidic).
Its molecular mass (or molar mass) is 98.08 g/mol and its molecular formula is H2SO4. The sulphur atom and two oxygen atom present in the sulphuric acid are bonded to each other via means of double bonds while the two hydrogen and two remaining oxygen atoms are present in the form of hydroxyl groups and linked to the central sulphur atom via means of single bonds. Its structure may be represented in the following manners:
Sulphuric acid is one of the most manufactured organic chemicals due to its wide range of applications across various industries. Here is a comprehensive list of the uses of sulphuric acid:
• One of the major uses of sulphuric acid is in the manufacturing of fertilisers. The most commonly used fertilisers which require sulphuric acid as one of their raw materials include lime superphosphate [Ca(H2PO4)2; which is a mixture of calcium dihydrogen phosphate – Ca(H₂PO₄)₂ and calcium sulphate or gypsum – CaSO₄·2H₂O] and ammonium sulphate [(NH₄)₂SO₄]. The superphosphate of lime is one of the most essential and important fertilisers used for acidic soils and is a restorer of phosphorus to the soils, making it alkaline and reduces its acidity. The main use of ammonium sulphate as a fertilizer is in the neutralization of the alkaline type of soils to lower the pH of the soil by producing mild and weak acidic conditions in the soil. It also helps in providing the nitrogen atom back to the soil which is one of the essential elements required for plant growth.
• In chemical industry, sulphuric acid is used in the production of a variety of organic chemicals such as organic acids like nitric acid and hydrochloric acid as well as certain Sulphur containing salts and other compounds. Sulphuric acid is also used in the manufacturing of certain very powerful alkylating agents such as dimethyl sulphate and various other esters and diesters derived from sulphuric acid. These alkylating agents are further used for a variety of chemical synthesis reactions and in the induction of chemical mutagenesis.
• Sulphuric acid is also used in the production of synthetic detergents such as LABSA (Linear Alkyl Benzene Sulphonic Acid). Sulphuric Acid is also used in the preparation of acid slurry (Dodecyl Benzene Sulphoric Acid), by suphonation of dodecylx benzene. This acid slurry produced is further used for the manufacture of various detergents and soaps.
• In colouring industry, sulphuric acid is used to prepare many dyes and pigments. One of the most famous colouring agents used industrially, titanium dioxide is prepared as a result of treatment of titanium-iron oxide mineral ore (also commonly known as ilmenite) with concentrated sulphuric acid and titanium oxygen sulphate (TiOSO4).
• Sulphuric acid is one of the components required for the preparation of explosives. TATP (Triacetone triperoxide) is an explosive which is prepared by taking hydrogen peroxide, acetone and sulphuric acid as the basic raw materials.
• Sulphuric acid finds a wide range of application in the pharmaceutical industry. It is used as a solvent for the chemical synthesis of a variety of chemical substances including active pharmaceutical ingredients. One type of active pharmaceutical ingredients manufactured by using sulphuric acid are the alkylating agents which are commonly used in the chemotherapy (treatment of cancer).
• In the petroleum industry, sulphuric acid is used to refine the extracted crude hydrocarbons as well as their refined products such as gasoline, jet fuel and diesel so as to remove all the organic impurities present in them. Also, Sulphuric acid is widely used for the extraction of sulphur from natural gas and oil since crude organic maters contain large quantities of sulphur present in the form of hydrogen sulphides. Refinement of these sulphide compounds results in the extraction of sulphur, a vital element for all living forms. Besides, sulphur is further used in many chemical processes such as the Bunsen Reaction for the production of hydrogen.
• Sulphuric acid is widely used in the process of metal processing. It finds its application mainly for the cleaning purposes in metals such as iron and steel. A special type of iron cleaning, specifically called as pickling, is done before it is made to undergo galvanization (metal plating with zinc so as to prevent it from rusting). Rather, sulphuric acid, itself, can also be used for the prevention of rusting when used for cleaning iron. It hence provides a double synergistic action against rusting or oxidation of iron.
• Sulphuric acid is used in the manufacturing of Rayon. To carry out this manufacturing, the raw cellulose fibers obtained from a natural source are dissolved in an aqueous solution which contains ions of tetraamine copper. The resulting solution is then injected into concentrated sulphuric acid, leading to the formation of fibers of Rayon (which is also commonly known as regenerated cellulose).
• Sulphuric acid also finds an application in the electrochemical reaction where it serves as an electrode. It is particularly used in the electrodes which make up the lead based acid storage battery cells which are quite commonly used in the automobile industry. In these type types of batteries, a particular concentration of pure sulphuric acid (33%), having a specific gravity of 1.25, is used.
• Sulphuric acid is one of the raw materials used in the paper and pulp industry for the production of chlorine dioxide, a powerful oxidising and bleaching agent which is used specifically for the bleaching of water (or chlorination of water) done commonly for the treatment of drinking water.
• Sulphuric acid is a good oxidizing agent and is used in many chemical reactions for the oxidation of a variety of substance. It, apart from being an oxidizing agent, is also widely used as a dehydrating agent for the dehydration of various sugars (such as sucrose or glucose) to form a solid black film of carbon as residue.
• In the agricultural industry, sulphuric acid finds its use in the harvesting of potato. A solution of sulphuric acid is sprayed on the potato fields before harvesting them so as to make the green tops of the potato plant dehydrated and then they eventually dry out. It makes it easy for the farmers to separate them before they could send the crop into the harvesting machine.
• Sulphuric acid is the medium in which all the esterification reactions take place. In chemistry, esterification reactions are used to produce a new class of organic compounds named esters as a result of the chemical reaction between an organic acid and an alcohol. The reaction is catalyzed in an acidic medium, provided by sulphuric acid.
• In household cleaning, sulphuric acid has been conventionally used for the cleaning of toilet seats and other dirty washroom areas like drains.
• Sulphuric acid, in very mild concentrations, is used in some topical ointments particularly for the treatment of canker sores. However, such ointments should be used with caution as they may cause irritation in some susceptible people. Since sulphuric acid is a very strong acid and dehydrating agent, its moderate or high concentrations may lead to severe skin burns, rashes or injuries. Hence it should be handled with utmost caution.
• Sulphuric acid acts as a catalyst in many chemical reactions carried out industrially. Some of the common examples of its use as a catalyst includes its inclusion in the reaction involving the production of caprolactam from cyclohexanone oxime. This caprolactam is further used for the production of nylon in the textile industry. Sulphuric acid also catalyses the reaction of production of isooctane from isobutane and isobutylene. This resultant product (isooctane, also known as trimethylpentane) is an anti-knocking agent used to increase the octane number of refined gasoline (produced from crude petroleum).
• Sulphuric acid is used in the production of another common mineral acid, hydrochloric acid, via a reaction known as the Mannheim Process. In this reaction, sodium chloride is made to react with hydrochloric acid which results in the production of hydrochloric acid and sodium bisulphate, as an intermediate product, which further reacts with sodium chloride again to produce another molecule of hydrochloric acid.
• Sulphuric acid is used in the preparation of Piranha Solution, (which is also known as Piranha) along with hydrogen peroxide. This solution is a very strong oxidising agent and is used for cleaning purposes, particularly in the microelectronics industry. However, this solution is highly toxic and should be used with great caution.
