Question

When 3 grams of sulfur are combined with 3 grams of oxygen, 6 grams of sulfur dioxide are formed. What mass of oxygen would be required to convert 3 grams of sulfur into sulfur trioxide

Answer 1

S + O2 ==> SO2
2SO2 + O2 ==> 2SO3
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Multiply equation 1 by 2 to obtain
2S + 2O2 ==> 2SO2 then add equation 2
2SO2 + O2 ==> 2SO3 to obtain
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2S + 3O2 ==> 2SO3
mols S in 3.00g S = 3.00/32 = 0.0938
Convert to mols oxygen using the final equation above as follows:
0.0938 mols S x (3 mols O2/2 mol S) = 0.0938 x 3/2 = ? mols O2, then
? mols O2 x 32 g O2/mol = ? grams O2.
Post your work if you get stuck.
You can do this another way. You know you have 3 g O2 from the problem to form SO2. So calculate the grams SO2 the firs equation gives you, use that to calculate the grams O2 to make SO3, then add the two together. Both answers should be the same.