Sulfuric acid is a colorless, dense, oily liquid that is extremely corrosive. It is one of the most important commercial chemicals, with many uses in production and manufacturing. Chemists classify sulfuric acid as a strong mineral acid.
Sulfuric acid is one of the strongest acids. It can burn the skin and irritate the lining of the nose, trachea (windpipe), and lungs. Safety standards established by the United States government protect industrial workers from overexposure to the acid or its fumes.
Uses and properties.
Sulfuric acid is used chiefly in the manufacture of fertilizer. Manufacturers of petroleum products use sulfuric acid in the refining of petroleum. Other manufacturers use it in the production of such items as automobile batteries, explosives, pigments, iron and other metals, and paper pulp.
The chemical industry uses sulfuric acid in producing many kinds of organic chemicals. For example, it is used in making alcohol from ethylene. Sulfuric acid reacts with benzene and other compounds to make sulfonates, which are used in powerful detergents. It is also used in making some dyes and medicines. The strength of sulfuric acid makes it useful in producing other acids and in removing soluble materials from minerals. Many metals dissolve in sulfuric acid and form sulfates (salts of the acid), which have important industrial uses (see Sulfate ).
Sulfuric acid combines quickly with water. The strong chemical attraction of sulfuric acid to water enables it to remove hydrogen and oxygen, the components of water, from many substances. This property makes it useful as a dehydrating agent. The dehydrating action of sulfuric acid can be shown with sugar, which contains carbon, hydrogen, and oxygen. When the acid is poured on sugar, the mixture decomposes and turns into black, foamy carbon “charcoal.”
Water and concentrated sulfuric acid react violently when they are combined, and the mixture becomes boiling hot. Small amounts of acid should be added slowly and carefully to water. Water should never be added to sulfuric acid. This action causes dangerous spattering.
Some sulfuric acid contains excess sulfur trioxide, a chemical that gives off gas when combined with moisture in the air. Chemists call this type of sulfuric acid oleum or fuming sulfuric acid. It is used in one of the methods of manufacturing sulfuric acid.
How sulfuric acid is made.
Commercial preparation of sulfuric acid was first described in the 1600’s. In the past, manufacturers mainly used the lead-chamber method to produce sulfuric acid. Today, the acid is primarily manufactured from sulfur by the contact method.
The lead-chamber method starts with the burning of sulfur to form sulfur dioxide. The sulfur dioxide then reacts with nitrogen compounds called nitric oxides in a lead-lined chamber, producing sulfuric acid. This process is inexpensive, but it produces relatively weak acid.
The contact method produces purer, more highly concentrated sulfuric acid than does the lead-chamber process. In the contact method, sulfur trioxide is made by passing sulfur dioxide, a colorless gas, through a heated reaction tube that contains either vanadium or platinum, each of which acts as a catalyst (see Catalysis ). Next, the sulfur trioxide is dissolved in concentrated sulfuric acid, forming oleum. The oleum is added to water to produce sulfuric acid of any desired concentration.
Sulfuric acid can also be produced from sulfur dioxide obtained as a by-product of roasting copper and iron pyrites and other sulfide ores. Roasting is a process used in separating and refining metal ores by heating the ores in air.
In the future, electric power plants that burn coal for fuel may provide a practical source of sulfuric acid. The acid could be produced from sulfur dioxide obtained by purifying gases released during coal combustion. But the many impurities in these gases make it difficult to collect sulfur dioxide in this manner. Also, the remote location of many power plants complicates the shipment of the highly corrosive sulfuric acid.
