Final answer:
To determine the unreacted fraction of the excess reactant in the FeS formation reaction, we calculate the number of moles of iron and sulfur using their atomic weights and find the limiting reactant.
Step-by-step explanation:
The question involves a stoichiometry calculation to determine the fraction of the original mass of excess reactant left unreacted after the formation of iron sulfide (FeS) from iron (Fe) and sulfur (S). Stoichiometry uses the concept of mole ratios derived from balanced chemical equations, allowing us to relate quantities of reactants and products.
To solve this problem, we must first determine the mole ratio of iron to sulfur in the reaction to form iron sulfide, which is 1:1. Using the atomic weights provided for iron (56) and sulfur (32), we calculate moles of each reactant and apply the mole ratio to determine the limiting reactant. Since the reactants are provided in equal mass, we find the number of moles by dividing the mass by the respective atomic weight.
By identifying the limiting reactant, we can then determine the mass of FeS produced and the mass of the excess reactant left unreacted. The fraction of the original mass of excess reactant that is unreacted is calculated by dividing the mass of unreacted reactant by the initial mass of the reactant and expressing it as a fraction.