30 points! how many moles of oxygen gas are needed to completely react with 145 grams of aluminum? report your answer with 3 significant figures. mole o2.

First a balanced reaction equation must be established:
    →    

Now if mass of aluminum = 145 g
the moles of aluminum = (MASS) ÷ (MOLAR MASS) = 145 g ÷ 30 g/mol
                                                                                    =  4.83 mols

Now the mole ratio of Al : O₂ based on the equation is  4 : 3  
                                                                [4Al  + 3 O₂ → 2 Al₂O₃]

∴ if moles of Al = 4.83 moles
  then moles of O₂ = (4.83 mol ÷ 4) × 3
                              =  3.63 mol   (to  2 sig. fig.) 

Thus it can be concluded that 3.63 moles of oxygen is needed to react completely with 145 g of aluminum. 

     

I’m guessing you’re more alert to yourself or your surroundings if you’re more concentrated

We can’t you if you only tell us that you have to show us what the answers are