Element with a mass of 16 g, interacts with molecular oxygen of a mass of 6.4 g, forms an oxide

Element with a mass of 16 g, interacts with molecular oxygen of a mass of 6.4 g, forms an oxide of the composition EO. Determine what kind of element it is

1. Let’s compose the reaction equation (E is an unknown element):
2E + O2 = 2EO;
2. Let’s find the amount of substance oxygen:
6.4 / 32 = 0.2 mol;
3. The unknown element has a coefficient 2 times greater than that of oxygen. The amount of substance in the unknown element is 0.4 mol. Let’s find the molecular weight of the unknown element:
16 / 0.4 = 40 g / mol;
The unknown element is calcium, the oxide of which has the formula CaO.
Answer: in the first problem the unknown element is sulfur, in the second it is calcium.