Answer
The mass of unreacted iron (III) oxide is 2.53 g.
Work Step by Step
Strategy: to find the mass of iron (III) oxide, we should apply the law of conservation of mass for the chemical reaction. Note however that it is written that at the end of the experiment, it was found that the final mixture contained an undetermined amount of unreacted iron (III) oxide. We should add this mass when we apply the law of conservation of mass.
1- Step one: Apply the law of conservation of mass for this chemical reaction:
m (of aluminum) + m (of iron (III) oxide) = m (of iron) + m (of aluminum oxide) + m (of unreacted iron (III) oxide)
By applying the law of conservation of mass, we can find the amount of unreacted iron (III) oxide.
2- Step two: Replace the mass of aluminum, mass of iron (III) oxide, mass of iron and mass of aluminum oxide, in order to find the mass of unreacted iron (III) oxide:
5.40 g + 18.5 g = 11.17 g + 10.20 g + m (of unreacted iron (III)
23.9 g = 21.37 g + m (of unreacted iron (III)
m (of unreacted iron (III) = 23.9 g – 21.37 g
m (of unreacted iron (III) = 2.53 g
2.53 g, is the mass of unreacted iron (III) oxide .