A 5.687 g sample of iron reacts with oxygen, forming an iron oxide. The final mass of the iron oxide is 8.131 g. What is the formula of the iron oxide

Fe₂O₃

Explanation:

Mass of Iron = 5.687 g

Mass of Iron oxide = 8.131 g

Mass of Oxide = Mass of Iron oxide - Mass of Iron

Mass of oxide = 8.131 - 5.687 = 2.444 g

Moles of Iron =  Mass / Molar mass = 5.687 / 55.845 = 0.1018 moles

Moles of Oxide  =  Mass / Molar mass = 2.444 / 16 = 0.15275 moles

To determine the formular, we have to find the smallest whole number ration that exists between the elements.

To do that, we divide by the smallest number;

Iron = 0.1018 / 0.15275 = 0.6664 = 2/3 (Approximately)

Oxygen = 0.15275 / 0.15275 = 1

To get the smallest whole number ratio, multiply all through by 3.

Iron = 2/3 * 3 = 2

Oxygen = 1 * 3 = 3

The formular will be;

Fe₂O₃

i believe you are right for all except the 3rd ( look at sqdancefan his answer is much better)