Sulfuric Acid in Chemical Industry

Sulfuric acid (H2SO4) also called oil of vitriol or hydrogen sulfate is an important strong dibasic acid uses for the production of fertilizer in the chemical plant industry and manufacture by the contact process. Oleum or fuming sulfuric acid is obtained by dissolving SO3 gases in concentrated H2SO4 solution and always dilute the concentration by slowly pouring water with stirring. Conc 98 percent of sulfuric acid uses as an effective dehydrating reagent with strong oxidizing properties. Annual about 150 million tons production of sulphuric acids of the whole world leaves 250000-ton sulfur per year on our environment which is responsible for acid rain or snow in the earth’s atmosphere.

Structure of Sulfate Ion

The sulfate ion and sulfuric acid structure contain tetrahedral with SP3 hybridized sulfur atom. Therefore, the electronic structure of the sulfate ion and acid are

Structure, production, properties, and uses of sulfuric acid (H2SO4)


  1. In structure A, sulfur has the 6+2 = 8 valence shell electrons which are distributed in four SP3 orbitals. This orbital makes four coordinate bonding to four oxygen atom.
  2. In structure B, sulfur has the 6+1 = 7 valence shell electrons. Among these two electrons particles, pairs use in two SP3 orbitals making the coordinate bonds. Two other hybrid quantum orbitals with one electron each overlap with oxygen p-orbitals to make one sigma bond each.

Chemical Properties  of H2SO4

Anhydrous Sulfuric or sulphuric acid is a colorless, heavy, viscous liquid with high dielectric constant and low pH level, reacts with strong bases for neutralization reaction.

Melting Point 10.4°C
Boling point ∼ 300°C
Density (ρ) 1.83 gm cm-3
Viscocity (η) 24.5 centipoise
Dielectric constant (ε) 100

The molecules are strongly hydrogen bonding in both the liquid and solid form and hydrogen ion or protons in water solution. It has several ionization constants presented as

H2SO4 + H2SO4 → H3SO4+ + HSO4
K (10°C) = 1.7 × 10-4 mol2 kg-2
H2SO4 + H2SO4 → H3O+ + HS2O7
K (10°C) = 3.5 × 10-5 mol2 kg-2
H2S2O7 + H2SO4 → H3SO4+ + HS2O7
K (10°C) = 7 × 10-2 mol2 kg-2

Hydration of conc H2SO4 libates a large amount of heat. Thus the sulfuric acid is always dilute by slowly pouring into the water with stirring. But reverse addition may cause explosive of the acid mixture by the stream formed. At low temperatures, this forms several crystals hydrates.

Reaction of Sulfuric Acid Solution

  • Concentrated H2SO4 has a great affinity for water and forms several crystalline hydrates. Therefore, it serves as an excellent drying agent. Cellulose materials such as paper, cotton, wood, and sugar are dehydrated by this solution.

C12H22O11 + 11H2SO4 → 12C + 11H2SO4, H2O

  • Metals above hydrogen atom in the electrochemical series (with positive standard redox potential) do not dissolve in cold or dilute sulfuric acid. Therefore, these metals dissolve in hot conditions because hot acid works as a good oxidant.

2Ag + H2SO4 → Ag2SO4 + SO2 + 2H2O
Cu + H2SO4 → CuSO4 + SO2 + 2H2O

Manufacture of Sulfuric Acid by Contact Process

The contact process is used for the manufacture of sulfuric acid. This process based on the oxidation of SO2 to SO3 on the vanadium peroxide catalyst promoted by potassium sulfate.

SO2 + ½O2 → SO3 ΔH0 = -98 kJ mol-1

Due to the exothermic reaction, the contact process gives higher equilibrium conversation at low temperatures and high pressure. But at low temperatures below 400°C, the rate of reaction becomes very slow and the V2O5 catalyst is inactive.

The conversation actually affected in four stages and working best around 450°C to 550°C. The SO2 produced in the contact process is absorbed by 98% conc sulfuric acid to form fuming or oleum. The oleum produced in the contact process subsequently diluted with water for the production of 98% sulfuric acid.

Uses of Sulfuric Acid in Chemical Industry

Sulfuric or sulphuric acid has great industrial uses for fertilizer production and manufacture by two methods both involving catalytic oxidation of SO2 to SO3.

  1. Sulfuric acid is widely used in the fertilizer industry to make ammonium sulfate and supersulfate.
  2. It is used to make ester, ethers, sulfates, and other acids.
  3. Fuming sulfuric acid is uses for sulfonation. In this process introducing -SO3H group in organic compounds.
  4. For the manufacture of paints, pigments, dyestuffs, fibers, detergents, and other chemicals elements we use huge quantities of concentrated H2SO4.