Question: how to calculate mass percent of oxygen in potassium chlorate?
Answer: Procedures: 1. ... 
mass of oxygen driven off___ x 100 = experimental percentage of oxygen in mass of potassium chlorate used KClO3
0.74 g x 100 = 37.6 %
3 mol O x 16.00 g/mol x 100 = 39.17 %
122.55 g/mol.
valueaccepted
0.772 g – 0.74 g x 100 = 4.14%
0.772 g.