When 2.50 g of copper reacts with oxygen the copper oxide product has a mass of 2.81 g. what is the simplest formula of the copper oxide?

In a chemical reaction, total mass of reactants should be equal to total mass of products. The total mass of copper oxide which has been produced during the reaction is 2.81 grams, at the beginning there were 2.50 grams of copper which leads us to the mass of Oxygen that has been used in the reaction. 2.50 grams of Copper + X grams of Oxygen = 2.81 grams of Copper Oxide, from this equation the total mass of Oxygen is 0.31 grams. Molar mass of Oxygen is 16 gram/mole so in this oxidation reaction 0.0194 mole of Oxygen is used (0.31/16). Molar mass of Copper is 63.546 gram/mole, in the reaction 0.0393 mole of copper used (2.50/63.546). In order to get the simplest formula, smallest number is used for proportioning. (0.0194/0.0194 = 1) 1 Oxygen (0.0393 / 0.0194 = app. 2) 2 Cu. Simplest formula for this reaction is Cu2O, Copper (I) oxide.