please need help in this chemistry question with a reasonable explanation

Question

You heat 3.854 g of a mixture of Fe3O4 and FeO to form 4.148 g Fe2O3. The mass percent of FeO originally in the mixture was:

A) 92.9%

B) 55.8%

C) 44.2%

D) 38.5%

Answer 1

To my way of thinking, you really don't need the balanced equation, nor the amount of oxygen incorporated. If we use moles and percent composition, we should be able to find the answer. My approach is as follows:

Fe₂O₃ = 159.69 g/mol

FeO = 71.845 g/mol

Fe₃O₄ = 231.533 g/mol

4.148 g Fe₂O₃ x 1 mol Fe₂O₃/159.69 g x 2 mol Fe/mol Fe₂O₃ x 55.85 g Fe/mol Fe = 2.901 g Fe in the product

Let x = g FeO and let y = g Fe₃O₄

x + y = 3.854 g

x = 3.854 g - y

2.901 g Fe = (3.854 - y)(55.85 g Fe/71.845 g FeO/mol) + y(167.55 g Fe/231.533 g Fe₃O₄/mol)

y = 1.679 g Fe₂O₃

x = 3.854 g - 1.679 g = 2.157 g FeO

Mass % FeO = 2.157 g/3.854 g (x100%) = 55.9% (ANSWER B)

Answer 2

To solve this problem, you need to consider the Law of Conservation of Mass. You have 3.854 g of reactants and 4.148 g of product. What accounts for the difference in mass? Oxygen!

Before attempting to balance the chemical equation, think about how to calculate the amount of oxygen included in the reaction.

4.148 g - 3.854 g = 0.294 g O₂

See if you can use this information to balance the chemical equation:

(a) Fe₃O₄ + (b) FeO + (c) O₂ --> (d) Fe₂O₃