What is the mass of oxygen in the copper oxide?

Question

- the initial mass of copper powder and the beaker: 83.620g

- the final mass of copper oxide and the beaker after the reaction: 89.920 g

- the gain in mass equal to the added mass of oxygen

- The number of moles of oxygen in the copper oxide, given a molecular weight of oxygen euqal to 16.00 g/mole

Answer 1

The oxygen added to the copper is 3.300 grams.  

  89.920 - 83.620 = 3.300 g oxygen

That is 0.2063 moles of oxygen.

  3.300 g O x (1 mol O / 16.00 g O) = 0.20625 mol O

Now, if we knew the mass of the beaker, we could determine the mass of the Cu, the moles of Cu and the empirical formula of the copper oxide.