A 1.56g sample of copper reacts with oxygen to form 1.95g of the metal oxide. What is the empirical formula?

Answer 1

grams O present = 1.95 g - 1.56 g Cu = 0.39 g

moles Cu = 1.56 g x 1 mol Cu/63.5 g = 0.0246 moles Cu

moles O = 0.39 g O x 1 mol O/16 g = 0.0244 moles O

Note that the mole ratio of Cu to O is 1:1 (~0.24 moles of each)

Empirical formula = CuO