A strip of electrolytically purified copper weighing 3.178 grams is strongly heated in a stream of oxygen until it is all converted to a black oxide.The resultant black powder weighs 3.978 g.What is the formula of the oxide?

Question

Quizplus · Accepted Answer

The increase in mass (3.978 g - 3.178 g = 0.800 g) is due to the oxygen that combined with copper. The molar mass of copper (Cu) is approximately 63.55 g/mol, and that of oxygen (O) is about 16.00 g/mol. The amount of copper is 3.178 g / 63.55 g/mol ≈ 0.050 mol, and the amount of oxygen is 0.800 g / 16.00 g/mol = 0.050 mol. Since the molar ratio of copper to oxygen is approximately 1:1, the formula of the oxide is CuO.

A Strip of Electrolytically Purified Copper Weighing 3