How many grams of Fe are needed to form 5 grams of Fe2O3?

Answer 1

We'll need to write the balanced equation for the formation of Fe2O3 from Fe. This is basically the formation of rust (iron oxide: Fe2O3) from iron (Fe).

4Fe + 3O₂ ==> 2Fe₂O₃ ... balanced equation

This tells us that 4 moles of Fe will react with 3 moles of O₂ to make 2 moles of 2Fe₂O₃. We will use this relationship to find the grams of Fe needed to react to form 5 grams of 2Fe₂O₃, BUT FIRST we must convert everything to MOLES and then back to GRAMS.

Molar mass 2Fe₂O₃ = 160 g / mol

Atomic mass Fe = 56 g / mol

5 g 2Fe₂O₃ x 1 mol 2Fe₂O₃ x 160 g = 0.031 mols 2Fe₂O₃

Using the balanced equation we find the moles of Fe needed:

0.031 mols 2Fe₂O₃ x 4 mols Fe / 2 mols 2Fe₂O₃ = 0.062 mols Fe needed

Converting this to grams of Fe, we have...

0.062 mols Fe x 56 g / mol = 3.47 g Fe = 3 g Fe (1 significant figure)