What is the % of free SO3 in an oleum, that is labelled 118%?
20%
40%
60%
80%
                
                  118% labelling means 18 g of water is added to 100 g of Oleum to yield 118 g of H2SO4
Weight of H2O added = 18 g
Moles of H2O added = 1
 Moles of SO3 present = 1
 Weight of SO3 in the 100g Oleum sample = 1 
 80 = 80 g
 % of free SO3 in Oleum = 80 %
Hence, the correct answer is Option (4)
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