How many grams of oxygen gas must react to give 2.80g of ZnO?

Answer 1

2Zn + O2 ---> 2 ZnO

Zn = 65
O = 16

ZnO = 81 g/mol

2.8 g / 81 g/mol = .0346 mol ZnO
half as many O2 mols = .0173 mol O2

.0173 * 32 g/mol = .553 mol O2