When iron reacts with oxygen, it forms iron oxide, or rust. 4 Fe + 3 O2 2 Fe2O3

If 112 g of iron (Fe) combines with 24 g of oxygen (O2), how much iron oxide is formed?

Mass of iron oxide: 79.85 g  

Explanation:

Given data:

Mass of iron = 112 g

Mass of O₂ = 24 g

Mass of iron oxide formed = ?

Solution:

4Fe + 3O₂         →       2Fe₂O₃

Number of moles of Fe:

Number of moles = mass/ molar mass

Number of moles = 112 g/ 55.85 g/mol

Number of moles =  2 mol

Number of moles of O₂:

Number of moles = mass/ molar mass

Number of moles = 24 g/ 32 g/mol

Number of moles =  0.75 mol

Now we will compare the moles of oxygen and iron with iron oxide.

                 Fe           :             Fe₂O₃

                 4             :                2

                 2             :                2/4×2 =  1

                O₂            :             Fe₂O₃

                 3             :                2

                 0.75       :                2/3×0.75 =  0.5

The number of moles of iron oxide formed by oxygen are less thus it will be limiting reactant.

Mass of iron oxide:

Mass = number of moles × molar mass

Mass = 0.5 mol  × 159.69 g/mol

Mass = 79.85 g