If 250g of iron react with oxygen gas to produce iron (iii) oxide, how many moles of oxygen gas will be needed?

= 3.358 moles

Explanation:

Iron react with oxygen to form iron(iii) oxide according to the following reaction;

4Fe(s) +3O2(g) → 4Fe2O3(S)

Moles of Iron in 250 g is;

= 250 g/55.845 g/mol

= 4.477 moles

Using mole ratio; Iron : oxygen = 4 : 3

Moles of oxygen gas = 4.477 × 3/4

                                   = 3.358 moles

Therefore. it means 3.358 moles of oxygen gas are required to react with 250 g of iron to form iron (ii) oxide.