4 Al(s) + 3 O2(g) ---> 2 Al2O3(s)
Use dimensional analysis and equation coefficients to convert moles of Al2O3 to moles of O2, to grams of O2:
[(1.00 mol Al2O3)/1][(3 mol O2)/(2 mol Al2O3)][(31.998 g O2)/(1 mol O2)] =
48.0 g of O2
