Stochiometry
Reaction
2Fe + O₂ ⇒ 2FeO
atomic mass Fe = 56 g/mol
molar mass FeO = 72 g/mol
moles of iron: 2.4 : 56 = 0.043
moles of FeO = 2.56 : 72 = 0.035
moles of FeO based on limiting reactant
because the coefficients of FeO and Fe are the same, then from the number of moles, Fe is an excess reactant
moles of oxygen: 1/2 x 0.035 = 0.0175
mass of oxygen: 0.0175 x 32 g/mol = 0.56 g
