Sulfuric acid (\(\text{H}_2\text{SO}_4\)) is a strong, inorganic mineral acid synthesized on a massive scale worldwide. It is often regarded as the single most important industrial chemical due to its pervasive use in manufacturing processes. The production volume of this substance is often used as an economic indicator of a nation’s industrial strength.
Physical Appearance of Concentrated Acid
Concentrated sulfuric acid, typically sold near 98% concentration, is a clear, colorless liquid. It has a noticeably high viscosity, meaning it flows with an oily texture, which led to its historical name “oil of vitriol”. Pure sulfuric acid is essentially odorless, though trace impurities can sometimes make it appear slightly yellow or brown. The liquid itself has a low volatility. Any visible “fumes” observed near an open container are not the acid vaporizing, but rather the acid absorbing water vapor directly from the air. This strong hygroscopic property causes the acid to pull moisture from the surrounding atmosphere, forming a fine mist of acid-water droplets.
Molecular Geometry and Atomic Structure
The structure of \(\text{H}_2\text{SO}_4\) dictates its function and is arranged around a central sulfur atom (S). This sulfur atom is chemically bonded to four oxygen atoms (O) in a three-dimensional arrangement. Two of these oxygen atoms are attached to hydrogen atoms (H), forming hydroxyl (\(\text{OH}\)) groups, while the other two oxygen atoms are double-bonded to the sulfur. The overall shape of the molecule with respect to the central sulfur atom is described as a tetrahedron. This tetrahedral structure gives the molecule stability and influences how it interacts with other chemical compounds.
Chemical Behavior and Reactivity with Water
Sulfuric acid is a powerful substance whose chemical nature makes it highly corrosive and reactive. Its corrosive action on materials and living tissue is partly due to its extremely strong acidic properties, which cause severe chemical burns. However, a more unique danger comes from its action as a dehydrating agent, meaning it has an intense affinity for water.
This dehydrating power is so strong that concentrated \(\text{H}_2\text{SO}_4\) can chemically remove the elements of hydrogen and oxygen (which form water) from organic compounds. For example, when applied to sugar or wood, the acid extracts the water elements, leaving behind elemental black carbon, a process known as charring. The reaction of \(\text{H}_2\text{SO}_4\) with water is also highly exothermic, meaning it releases a large amount of heat.
Mixing the concentrated acid with water must always be done by slowly adding the acid to the water, and never the reverse. This safety measure is necessary because water is less dense than the concentrated acid and will float on top of it. If water is poured onto the acid, the intense heat released from the reaction at the surface can instantly boil the water, resulting in the violent splattering of hot, corrosive acid.
Common Industrial and Consumer Applications
Sulfuric acid’s widespread industrial use stems from its low cost and high reactivity. Its single largest application, consuming over 80% of global production, is in the manufacture of fertilizers. It is used to produce phosphate and ammonium sulfate fertilizers, which are essential for supporting global agriculture.
Sulfuric acid is also widely used as the electrolyte in lead-acid batteries, often referred to as “battery acid”. This liquid facilitates the chemical reaction that stores and releases electrical energy in car batteries and backup power systems.
Other major uses include metal processing, such as “pickling” steel to remove rust and impurities. It also plays a role in producing various chemicals like detergents, synthetic resins, and dyes.