 Okay, goal. So let's try this problem here. How many grams of aluminum will react with 3 grams of oxygen? Okay, so we got the balanced equation here and we're just looking for the ratio of aluminum to oxygen. So it's a 4 to 3 ratio. So we know the mass of oxygen, O2, the mass and grams that we got. So we've got that mass of O2. That equals 3.00 grams. But in order to use the chemical equation, we've got to convert this to moles. So the number of moles of oxygen is going to equal the mass 0.00 grams times something that cancels grams and gives us moles. That something is the molecular weight of the molar mass. The molar mass of oxygen is 2 times 16.00 grams per mole, 32.00 grams per mole. We put 32.00 times the grams. Cancel those out. And all we have to do is use our calculator. Take 3 divided by 32 and we get 0.093. Okay, well that gives us the moles of O2, but we don't care about that. We care about the grams of Al. And in order to get the grams of Al, we've got to learn what the moles of Al are. So the moles of aluminum of oxygen, the ratio of oxygen to aluminum. So we take the moles of oxygen, 0.0, 9, 3 moles O2, or above that, 4 moles Al. So now hopefully you see that moles of O2 will cancel out. And we get 0.938 times 4 divided by 3. So our number of moles of Al is going to be 0.125. We don't need the moles, we need the grams of Al. So the mass of Al is going to be 0.125 moles for every 1 mole, 70 grams. 26.98 grams. 26.98 grams for every mole of Al. Those cancel out. 1.25 times 26.98 gives us the moles of Al. 3.37 grams. So 3.37 grams of Al will react with 3.0 grams of oxygen.