Question

What mass of potassium nitrate would you have in order to produce 1.00dm of oxygen at rtp?

Answer 1

Use PV = nRT; substitute rtp conditions and solve for n.

Then 2KNO3 ==> 2KNO2 + O2

You know mols O2 from above. Then
mols KNO3 = mols O2 from above x (2 mol KNO3/2 mols O2).
Finally, grams KNO3 = mols KNO3 x molar mass KNO3.