A sample of an oxide of iron was analyzed and found to contain 70 % of iron by mass. Assuming the remaining mass is entirely due to oxygen, which of the following represents the empirical formula of this oxide? [Given atomic masses: Fe = 56 u , O = 16 u ]

Step-by-step solution

Let the total mass of the oxide sample be 100 g . Mass of iron ( Fe ) = 70 g Mass of oxygen ( O ) = 100 g - 70 g = 30 g Number of moles of Fe = 70 56 = 1.25 mol Number of moles of O = 30 16 = 1.875 mol Molar ratio of Fe : O = 1.25 : 1.875 Dividing by the smaller value ( 1.25 ): Ratio = 1 : 1.5 Multiplying by 2 to obtain a whole number ratio: Ratio = 2 : 3 The empirical formula of the oxide is Fe ₂ O ₃ . Answer: Fe ₂ O ₃