Sulfuric acid (alternative spelling sulphuric acid) is a mineral acid with molecular formula H2SO4. It is a colorless odorless syrupy liquid that is soluble in water, in a reaction that is highly exothermic.Its corrosiveness can be mainly ascribed to its strong acidic nature. It is also hygroscopic, readily absorbing water vapour from the air. Sulfuric acid at even moderate concentrations is very dangerous upon contact with skin.
Sulfuric acid is a very important commodity chemical, and indeed, a nation's sulfuric acid production is a good indicator of its industrial strength. It is widely produced with different methods, such as contact process, wet sulfuric acid process, lead chamber process and some other methods.
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[clarification needed] 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.
Hydrogen peroxide (H2O2) can be added to sulfuric acid to produce piranha solution, a powerful but very toxic cleaning solution with which substrate surfaces can be cleaned. Piranha solution is typically used in the microelectronics industry, and also in laboratory settings to clean glassware.
