Oleum

From Freepedia

Oleum refers to the result of combining sulfur trioxide and sulfuric acid.

Oleums can be described by the formula xSO₃.H₂O. The value of x can be varied, to include different oleums, and this is how they are often described.

A common value for x is 2, for which we get the empirical formula H₂S₂O₇: this is mainly disulfuric acid; however in this case, as with others, one should not assume that the formula describes the sole molecular species involved: in every case, the result is a complex mixture of compounds in equilibrium.

Oleum is an important chemical used in the manufacture of sulfuric acid. If SO₃ is added directly to water, it tends to polymerize rather than form sulfuric acid. If SO₃ is added to sulfuric acid instead, it forms oleum which can then be mixed with water to form more sulfuric acid.

If poured onto powdered glucose, it will draw the hydrogen and oxygen out of the glucose in an exothermic reaction, leaving only carbon. This expands out of the container, hardening as a solid black substance with gas bubbles in it. Oleum is highly corrosive.