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ACIDS > Sulfuric Acid

Sulfuric acid is a highly corrosive strong mineral acid with the molecular formula H2SO4. It is pungent-ethereal, colorless to slightly yellow viscous liquid which is soluble in water at all concentrations.

Formula: H2SO4, Density: 1.84 g/cm³, Melting point: 10 °C, Molar mass: 98.079 g/mol, IUPAC ID: Sulfuric acid, Boiling point: 337 °C, Classification: Sulfuric acids


Uses :

Sulfuric acid production in 2000

Sulfuric acid is a very important commodity chemical, and indeed, a nation's sulfuric acid production is a good indicator of its industrial strength.World production in 2004 was about 180 million tonnes, with the following geographic distribution: Asia 35%, North America (including Mexico) 24%, Africa 11%, Western Europe 10%, Eastern Europe and Russia 10%, Australia and Oceania 7%, South America 7%.Most of this amount (~60%) is consumed for fertilizers, particularly superphosphates, ammonium phosphate and ammonium sulfates. About 20% is used in chemical industry for production of detergents, synthetic resins, dyestuffs, pharmaceuticals, petroleum catalysts, insecticides and antifreeze, as well as in various processes such as oil well acidicizing, aluminium reduction, paper sizing, water treatment. About 6% of uses are related to pigments and include paints, enamels, printing inks, coated fabrics and paper, and the rest is dispersed into a multitude of applications such as production of explosives, cellophane, acetate and viscose textiles, lubricants, non-ferrous metals and batteries.
Industrial production of chemicals

The major use for sulfuric acid is in the "wet method" for the production of phosphoric acid, used for manufacture of phosphate fertilizers. In this method, phosphate rock is used, and more than 100 million tonnes are processed annually. This raw material is shown below as fluorapatite, though the exact composition may vary. This is treated with 93% sulfuric acid to produce calcium sulfate, hydrogen fluoride (HF) and phosphoric acid. The HF is removed as hydrofluoric acid. The overall process can be represented as:

    Ca5F(PO4)3 + 5 H2SO4 + 10 H2O → 5 CaSO4·2 H2O + HF + 3 H3PO4

Ammonium sulfate, an important nitrogen fertilizer, is most commonly produced as a byproduct from coking plants supplying the iron and steel making plants. Reacting the ammonia produced in the thermal decomposition of coal with waste sulfuric acid allows the ammonia to be crystallized out as a salt (often brown because of iron contamination) and sold into the agro-chemicals industry.

Another important use for sulfuric acid is for the manufacture of aluminium sulfate, also known as paper maker's alum. This can react with small amounts of soap on paper pulp fibers to give gelatinous aluminium carboxylates, which help to coagulate the pulp fibers into a hard paper surface. It is also used for making aluminium hydroxide, which is used at water treatment plants to filter out impurities, as well as to improve the taste of the water. Aluminium sulfate is made by reacting bauxite with sulfuric acid:

    2 AlO(OH) + 3 H2SO4 → Al2(SO4)3 + 4 H2O

Sulfuric acid is also important in the manufacture of dyestuffs solutions.

Sulfur-iodine cycle

The sulfur-iodine cycle is a series of thermo-chemical processes used to obtain hydrogen. It consists of three chemical reactions whose net reactant is water and whose net products are hydrogen and oxygen.

    2 H2SO4 → 2 SO2 + 2 H2O + O2(830 °C) I 2 + SO2 + 2 H2O → 2 HI + H2SO4 (120 °C)2 HI → I 2 + H2(320 °C)

The sulfur and iodine compounds are recovered and reused, hence the consideration of the process as a cycle. This process is endothermic and must occur at high temperatures, so energy in the form of heat has to be supplied.

The sulfur-iodine cycle has been proposed as a way to supply hydrogen for a hydrogen-based economy. It does not require hydrocarbons like current methods of steam reforming. But note that all of the available energy in the hydrogen so produced is supplied by the heat used to make it.

The sulfur-iodine cycle is currently being researched as a feasible method of obtaining hydrogen, but the concentrated, corrosive acid at high temperatures poses currently insurmountable safety hazards if the process were built on a large scale.

Industrial cleaning agent

Sulfuric acid is used in large quantities by the iron and steelmaking industry to remove oxidation, rust and scaling from rolled sheet and billets prior to sale to the automobile and major appliances industry[citation needed]. Used acid is often recycled using a spent acid regeneration (SAR) plant. These plants combust spent acid with natural gas, refinery gas, fuel oil or other fuel sources. This combustion process produces gaseous sulfur dioxide (SO2) and sulfur trioxide (SO3) which are then used to manufacture "new" sulfuric acid. SAR plants are common additions to metal smelting plants, oil refineries, and other industries where sulfuric acid is consumed in bulk, as operating a SAR plant is much cheaper than the recurring costs of spent acid disposal and new acid purchases.


Sulfuric acid is used for a variety of other purposes in the chemical industry. For example, it is the usual acid catalyst for the conversion of cyclohexanone oxime to caprolactam, used for making nylon. It is used for making hydrochloric acid from salt via the Mannheim process. Much H2SO4 is used in petroleum refining, for example as a catalyst for the reaction of isobutane with isobutylene to give isooctane, a compound that raises the octane rating of gasoline (petrol).

Acidic drain cleaners usually contain sulfuric acid at a high concentration which turns a piece of pH paper red and chars it instantly, demonstrating the strong acidic nature and dehydrating property.

Sulfuric acid acts as the electrolyte in lead-acid (car) batteries (lead-acid accumulator):

At anode:

    Pb + SO42− ⇌ PbSO4 + 2 e−

At cathode:

    PbO2 + 4 H+ + SO42− + 2 e− ⇌ PbSO4 + 2 H2O

An acidic drain cleaner can be used to dissolve grease, hair and even tissue paper inside water pipes.


    Pb + PbO2 + 4 H+ + 2 SO42− ⇌ 2 PbSO4 + 2 H2O

Domestic uses

Concentrated sulfuric acid is frequently the major ingredient in acidic drain cleaners which are used to remove grease, hair, tissue paper, etc. Similar to their alkaline versions, such drain openers can dissolve fats and proteins via hydrolysis. Moreover, as concentrated sulfuric acid has a strong dehydrating property, it can remove tissue paper via dehydrating process as well. Since the acid may react with water vigorously, such acidic drain openers should be added slowly into the pipe to be cleaned.


Sulfuric acid and sulfonated phenolics are the primary ingredients in Debacterol, a liquid topical agent that is used in the treatment of recurrent aphthous stomatitis (canker sores/mouth ulcers) or for any procedures in the oral cavity which require controlled, focal debridement of necrotic tissues.