posted by deven .
If you have 13.0g of Na, how many grams of O2 are required for the reaction?
If Na2O is formed it is
4Na + O2 ==> 2Na2O
mols Na = 13.0/atomic mass Na.
mols O2 = 1/4 mols Na.
g O2 = mols O2 x molar mass O2.
If the reaction is the formation of Na2O2 then you have
2Na + O2 --> Na2O2
You can work it out from there, right?