Given 4Fe(s) + 3O2(g) ➡️ 2Fe2O3(g)

Question

how many grams of solid iron reacts when 7.986g of Fe2O3(s) is produced?

Answer 1

The units of the chemical reaction equation are moles so we need to convert the 7.986 g of Fe₂O₃ into moles to use the equation. We do that using the molar mass, which we need to calculate:

Fe → 2 x 55.845 = 111.69

O → 3 x 15.999 = 47.997

111.69 + 47.997 = 159.687 g/mol

7.986 g / 159.687 g/mol = 0.05 moles of Fe₂O₃

Since there are twice as many moles of solid iron required per mole of Fe₂O₃ produced (molar ratio is 4:2), we can multiply the 0.05 moles of Fe₂O₃ by 2 to get 0.10 moles of Fe.

Now we can multiply 0.10 moles x 55.845 g/mol to get 5.585 g of Fe (using 4 sig figs)