300cm^3 of Co is mixed and sparkled with 400cm^3 of air containing 21% of oxygen if all the volumes are measured at S.T.P calculate the total volume of residual gases

Answer 1

You have 300 cc Co with a density of 8.9 g/cc - >? grams. Then mols Co = g/atomic mass = approx 45. The oxygen in 400 cc air = 400 x 0.21 = about 84 cc and 84/22,400 = about 0.004 moles which is just a long way of telling you that the oxygen in the air is the limiting reagent and ALL of the oxygen in the air is used. So what's left? Just the nitrogen and other gases; i.e., 79%. So 400 x 0.79 = ? cc other gases = ? residual gases.