Sulfur dioxide (SO2) reacts with oxygen gas to make sulfur trioxide (SO3).

Question

How many grams of oxygen are used to produce 8.11 grams of sulfur trioxide?

Answer 1

2SO2 + O2 ==> 2SO3

mols SO3 needed = grams/molar mass = ?
Using the coefficients in the balanced equation, convert mols SO3 to mols O2.

Now convert mols O2 to grams. g O2 = mols O2 x molar mass O2.