Sulfuric Acid (H₂SO₄) — Properties, Uses & Safety

Overview

Sulfuric acid (H2SO4) is the most produced industrial chemical in the world, with global production exceeding 260 million tons per year — so fundamental to industry that a nation's sulfuric acid consumption has been used as an indicator of its economic development. With a molar mass of 98.08 g/mol, sulfuric acid is a dense, oily, colorless liquid that is highly corrosive and exothermic when mixed with water. It is a strong diprotic acid, meaning it can donate two protons (H⁺ ions) in sequential ionization steps: H2SO4 → H⁺ + HSO4⁻ (complete dissociation) and HSO4⁻ ⇌ H⁺ + SO4²⁻ (partial dissociation, Ka2 = 0.012). Sulfuric acid is manufactured industrially by the Contact Process: sulfur is burned to produce SO2, which is catalytically oxidized to SO3 using vanadium pentoxide (V2O5) catalyst, and SO3 is then absorbed in concentrated sulfuric acid to form oleum, which is diluted to the desired concentration. The Contact Process is a classic example of industrial catalysis and equilibrium optimization studied in chemistry courses. The applications of sulfuric acid are extraordinarily diverse. The largest single use is in the production of phosphoric acid and phosphate fertilizers (the wet acid process). Other major uses include petroleum refining (alkylation), lead-acid battery electrolyte (car batteries), metal processing and pickling, production of detergents and synthetic fibers, ore processing (leaching), and as a laboratory reagent. Sulfuric acid is also a powerful dehydrating agent — it can char sugar (C12H22O11 → 12 C + 11 H2O) in a dramatic demonstration of its water-removing ability. Safety considerations are paramount with sulfuric acid. Concentrated sulfuric acid causes severe chemical burns on contact with skin and can cause permanent blindness. The dilution of sulfuric acid is highly exothermic — the cardinal rule is always add acid to water, never water to acid, to prevent dangerous spattering. GHS pictograms include the corrosion symbol. For chemistry students, sulfuric acid connects to acid-base chemistry, diprotic acid equilibria, industrial chemistry and the Contact Process, Le Chatelier's principle, dehydration reactions, and laboratory safety protocols. It is arguably the single most important compound in industrial chemistry.

IUPAC Name

sulfuric acid

CAS Number

7664-93-9

PubChem CID

1118

Molecular Formula

H₂SO₄

Molar Mass

98.079 g/mol

State at STP

liquid

Appearance

Colorless oily liquid; fuming if concentrated