Concentrated Sulphuric Acid

Concentrated Sulphuric acid (also spelled sulfuric acid) is a highly corrosive, strong mineral acid with the chemical formula H₂SO₄. It is one of the most widely produced and used industrial chemicals in the world, often called “oil of vitriol” historically.

Physical and Chemical Properties

• Appearance: Colorless, odorless, viscous (oily) liquid when pure. It can appear yellow to dark brown when impure.
• Molar mass: 98.08 g/mol.
• Density: About 1.84 g/cm³ (for concentrated acid).
• Melting point: ~10.3°C (51°F).
• Boiling point: ~337°C (begins to decompose around 300°C, releasing sulfur oxides).
• Solubility: Completely miscible with water, but the mixing process is highly exothermic (releases a lot of heat). Always add acid to water slowly—never water to acid—to avoid violent splattering or boiling.

It is a strong acid that fully ionizes in water (first to HSO₄⁻, then to SO₄²⁻) and acts as a powerful dehydrating agent, oxidizing agent, and sulfonating agent. It chars organic materials (like wood or sugar) by removing water from them and reacts vigorously with many metals, bases, and organics.

Production

The primary modern method is the contact process:

1. Burn sulfur or roast sulfide ores to produce sulfur dioxide (SO₂).
2. Catalytically oxidize SO₂ to sulfur trioxide (SO₃) using vanadium(V) oxide catalyst.
3. Absorb SO₃ into concentrated sulfuric acid to form oleum (H₂S₂O₇), then dilute with water to get H₂SO₄.

This process allows production of very concentrated acid efficiently. Global production exceeds 300 million tonnes annually, with growth expected in the coming years driven by fertilizer demand.

Major Uses

Sulfuric acid is essential to many industries:

• Fertilizers (largest use): Produces phosphoric acid for phosphate fertilizers and ammonium sulfate.
• Petroleum refining: Alkylation processes and removal of impurities.
• Metal processing: “Pickling” (cleaning) steel, producing copper, zinc, and other metals.
• Batteries: Electrolyte in lead-acid car batteries (dilute form, often called “battery acid”).
• Chemicals: Manufacture of hydrochloric acid, nitric acid, dyes, detergents, explosives, pharmaceuticals, and more.
• Other: Wastewater treatment, paper/pulp processing, and as a laboratory reagent or drain cleaner (in diluted or specific forms).

Safety and Hazards

Sulfuric acid is extremely dangerous:

• Corrosive: Causes severe chemical burns to skin, eyes, and respiratory tract. Eye contact can lead to permanent blindness; skin contact can cause deep burns and tissue destruction.
• Dehydrating effect: It pulls water from tissues, worsening damage and potentially causing secondary thermal burns.
• Inhalation: Mists or vapors irritate or damage lungs; strong inorganic acid mists are classified as carcinogenic.
• Reactivity: Reacts violently with water, bases, metals (producing flammable hydrogen gas), and organics. Can generate toxic sulfur oxide fumes when heated.
• Chronic effects: Repeated low-level exposure can erode teeth and damage lungs.

Handling rules:

• Use in a fume hood with full PPE: chemical-resistant gloves (e.g., nitrile or neoprene), goggles/face shield, lab coat or full suit, and respiratory protection if needed.
• Store in compatible containers (glass, certain plastics, or lined tanks); keep away from water, organics, and metals.
• In case of spills: Neutralize carefully with bases like sodium bicarbonate (but expect heat and gas evolution); contain and dispose as hazardous waste.