A sample of sulfur having a mass of 1.28 g combines with oxygen to form a compound with a mass of 3.2g. What is the empirical formula. So what i did is found the mass of oxygen which is 1.92g . Then converted the 1.28g S to 0.04 mol. Then converted the 1.92g O2 (as it says oxygen, or should it be just O?) to get 0.24mol O. I found online that the answer should be SO3, but I get SO6 because of Oxygen. Should I not assume it is diatomic, and just go with as just element?