Answer:
26.18 g
Explanation:
The molar volume of oxygen at 1 atm and 0ºC is 22.4 L/mol.
If you want to react 7 L it means you will use
7/22.4 = 0.3125 moles of oxygen
the balanced equation is 3 Fe + 2 O2 = Fe3O4
which means that 2 moles of oxygen reacts with 3 moles of iron
If you have 0.3125 moles of oxygen, 0.468 moles of iron will be needed.
Iron molecular weight is 55.84 and than, 0.3125 moles corresponds to a mass of iron equal to 26.18
