How many grams of aluminum are needed to react with 192 g of oxygen gas?

First determine the balanced chemical reaction:

4Al + 3O2 ---> 2Al2O3

Next figure out the number of moles of oxygen you start with by dividing 192 by the molecular weight of oxygen (16 g/mol). Then use the coefficients from the reaction to determine how many moles of Al would need to react with the oxygen to convert all the oxygen and aluminum to aluminum oxide.

192 g * (1 mol O / 16 g O) * (4 moles of Al/6 moles of O) = 8 mol of Al

Finally multiply by the molecular weight of Aluminum to figure out the mass:

8 mol Al * (27 g/mol) = 216 g of Al