Sulfuric acid

Sulfuric acid
Molecular structure of sulfuric acid.
Properties
Boiling Point	337°C
Density	1.83 g/cm3

Sulfuric acid is a very strong mineral acid. Its chemical composition is H₂SO₄. Its principle use is in car batteries, followed by fertilizers.

Production

One way sulfuric acid is made is with the double contact process. The sulfur dioxide and air are mixed and heated to 450 ˚C and passed over a catalyst. Sulfur dioxide is oxidized to sulfur trioxide. Then the sulfur trioxide is cooled and passed through two towers. In the first tower it is washed with oleum. In the second tower it is washed with 97% sulfuric acid.
${\ce {2SO2 + O2 <=> 2SO3}}$
$\ce{SO3 + H2O = H2SO4}$

Reaction with water

The hydration reaction of sulfuric acid is highly exothermic. If water is added to the concentrated sulfuric acid, it can boil and spit dangerously. One should always add the acid to the water rather than the water to the acid. The necessity for this safety precaution is due to the relative densities of these two liquids. Water is less dense than sulfuric acid, meaning water will tend to float on top of this acid. The water is also able to absorb heat faster than acid, preventing a dangerous boil over. The reaction is best thought of as forming hydronium ions, oxygen atoms from other compounds; for example, mixing starch

$\ce{(C6H12O6)n}$

and concentrated sulfuric acid will give elemental carbon and water which is absorbed by the sulfuric acid (which becomes slightly diluted):

$\ce{(C6H12O6)n = 6C + 6H2O}$

The effect of this can be seen when concentrated sulfuric acid is spilled on paper; the cellulose reacts to give a burned appearance, the carbon appears much as soot would in a fire. A more dramatic reaction occurs when sulfuric acid is added to a tablespoon of white sugar; a rigid column of black, porous carbon will quickly emerge. The carbon will smell strongly of caramel as similar compounds are made from the pyrolysis of sugar.

This is a diagram of a machine used to create sulfuric acid.