Sulfuric acid

sulfuric acid
IUPAC name: sulfuric acid Synonyms: sulphuric acid and others Formula: H2SO4
Uses:	acid, dehydration, reduction
Properties:	strong acid
Hazards:	Toxic, Corrosive
Mass (g/mol): CAS #: 98.08 7664-93-9

Sulfuric acid, also spelled sulphuric acid, is a strong, corrosive acid and oxidizing agent having the chemical formula H₂SO₄. It is the diprotic acid of the sulfate anion SO₄^-2. At room temperature and pressure, it is a clear, colorless, rather viscous liquid. Sulfuric acid is one of the most important chemicals in the chemical industry. Personal protective gear should be worn when using sulfuric acid.

Synonyms

Sulfuric acid is also called oil of vitriol, mattling acid, vitriol, battery acid, dipping acid, electrolyte acid, vitriol brown oil, sulphuric acid, Babcock acid and sulphuric acid.

Properties and uses of sulfuric acid

Sulfuric acid is a strong acid, an oxidizing agent and a dehydrating agent. Two hydrogen ions can dissociate from H₂SO₄. In an aqueous (water) solution, the first hydrogen dissociates completely (100%) to form the bisulfate anion HSO₄^-. Since this dissociation is complete, sulfuric acid is considered a strong acid. HSO₄^- is a medium strength acid from which the second hydrogen dissociates to form the sulfate anion SO₄^-2.

H₂SO₄ + H₂O → H₃O⁺ + HSO₄⁻    K₁ = 2.4 x 10⁶   (strong acid)

HSO₄⁻ + H₂0 → H₃O⁺ + SO₄²⁻     K₂ = 1.0 x 10^-2  

K₁ and K₂ are the acid dissociation constants.

Sulfuric acid is used to make many soluble phophates for fertilizers, ammonium sulfate and many other chemicals, including drugs. Newly made steel is cleaned with sulfuric acid to remove rust before the steel is coated with a protective layer of zinc, tin or enamel. It is also used in lead sulfate batteries. Many explosives are manufactured using sulfuric acid.

Because it has a high boiling point (33°C), it can be used to make other more volatile acids using the appropriate acid salt. Nitric acid can be made by reacting sulfuric acid with sodium nitrate, NaNO₃. Distilling the resultant nitric acid (BP=86°C) drives the reaction towards completion.

NaNO₃ + H₂SO₄ → HNO₃ + NaHSO₄

Contact of water and sulfuric acid is exothermic. When handling them, always add acid to water, not the reverse or the resulting boiling can spray hot acid.

The explosive nitroglycerin (glyceryl trinitrate), is made by reacting glycerine and nitric acid in the presence of sulfuric acid. This reaction is very dangerous, do not attempt.

C₃H₅(OH)₃ + 3HNO₃ + (H₂SO₄ catalyst)→ C₃H₅(NO₃)₃ + 3H₂O.

Sulfuric acid can be used as a drying agent for gases that do not react with sulfuric acid by bubbling the gas through sulfuric acid.

Synthesis of sulfuric acid

Sulfuric acid is made be reacting sulfur trioxide with water in an exothermic reaction.

SO₃(g) + H₂O(l) → H₂SO₄(l) + 130 kJ mole^-1

In the commercial production of sulfuric acid, the contact process or the lead-chamber process is used. In the contact method, sulfur dioxide is catalytically converted to sulfur trioxide by surface chemistry with fine platinum powder or, more recently, vanadium pentoxide (V₂O₅). The resulting sulfur trioxide gas is bubbled through sulfuric acid and the addition of water at the correct rate yields 98% acid pulled out.

The lead-chamber process uses sulfur dioxide, oxygen, nitric acid and water vapor are introduced into a lead-lined chamber. White crystals of nitrosulfuric acid (nitronium sulfate), NOHSO₄, are formed. The introduction of steam then converts the nitrosulfuric acid to sulfuric acid liberates nitrogen oxides, which can be reused in the first step of the reaction.

1) 2SO₂ + NO + NO₂ + O₂ + H₂O → 2NOHSO₄

2) 2NOHSO₄ + H₂O → 2H₂SO₄ + NO + NO₂

Soluble and insoluble sulfate salts

The soluble salts of sulfate include sodium sulfate (Na₂SO₄)•10H₂O, ammonium sulfate (NH₄)₂SO₄, magnesium sulfate (Epsom salt, MgSO₄•7H₂O, copper sulfate (blue vitriol, CuSO₄•5H₂O), iron sulfate (FeSO₄•7H₂O), zinc sulfate (ZnSO₄•7H₂O), potassium aluminium sulfate (alum, KAl(SO₄)₂•12H₂O), ammonium aluminium sulfate (ammonium alum, NH₄Al(SO₄)₂•12H₂O), and chrome alum (KCr(SO₄)₂•12H₂O).

Barium sulfate (barite) is the least soluble sulfate salt and its white precipitate is used as a test for sulfate anions. Other sulfates with diminished solubility include lead sulfate (PbSO₄), strontium sulfate (SrSO4) and calcium sulfate (gypsum, CaSO₄•2H₂O.