Question

What is `"sulfur trioxide"`?

Answer 1

Sulfur trioxide is the acid anhydride of sulfuric acid.

Explanation:

`SO_2(g) + 1/2O_2(g) rarr SO_3(g)`

`SO_3(g) + H_2O(l) rarr H_2SO_4(aq)`

Oleum, fuming sulfuric acid is concentrated sulfuric acid saturated (sometimes it is less concentrated) with `SO_3(g)`.