How much oxygen is needed to burn 3.00g of magnesium to form magnesium oxide? How can I illustrate in the Law of Conservation of Mass?

Answer 1

2Mg + O2 ==> 2MgO
mol Mg = g/atomic mass = 3.00 g/24.3 = 0.123
mols O2 required = (1/2)*0.123 = 0.0617
grams O2 = 0.0617 x 32 g = 1.97
Law conservation of mass says you don't gain or lose mass. So
Total MgO produced should be 3.00 + 1.97 = 4.97 g
NOTE: You can calculate how much MgO is produced. Since 1 mol Mg produces 1 mol MgO, then 0.123 mols MgO will be 0.1234 x 40.3 = 4.97 g MgO.