What is oleum? If s given sample is marked as 106.75% oleum, what does it mean? Also calculate the % of free SO3 in it.
Oleum refers to the various compositions of sulfur trioxide in sulfuric acid. It refers to disulfuric acid (also known as pyrosulfuric acid) sometimes. Oleum is also called as fuming sulphuric acid.
It is not 106.75% oleum it is 106.75%H2SO4 labelled oleum because 30% oleum (SO3)=106.75% H2SO4
Oleum is generally assayed according to the free SO3 content by weight. It can also be expressed as a percentage of sulfuric acid strength; for oleum concentrations, that would be over 100%. For example, 10% oleum can also be expressed as H2SO4.0.10889SO3, 1.0225SO3.H2O or 102.25% sulfuric acid. The conversion between % acid and % oleum is: % acid = 100 + 18/80 * % oleum
Calculation of free SO3 in 106.75% H2SO4 labelled oleum.
We know that,
H2O + SO3 -------------> H2SO4
As 18 g of water combines with 80 g SO3, therefore
6.75 g of water combines with (6.75*80)/18 = 30 g of SO3
100 g of oleum contains 30 g of SO3
Or 30% free SO3