1. The problem statement, all variables and given/known data When M2S3 is heated in air, it is converted to MO2. A 4.000g sample of M2S3 shows a decrease in mass of .277 g when it is heated in air. What is the average atomic mass of M? 2. Relevant equations 3. The attempt at a solution I dont not really know how to tackle this problem. I know the mass of MO2 would be 3.833g.