Fe2O3 oxid feric M(masa moleculara)=2.56+3.16=160
160goxid-----------112gFe---------48gO
100g----------------x-------------------y
x=100.112:160=70 la suta Fe
y=100.48:160=30 la suta O
FeO oxid feros M=56+16=72
72gFeO-----------56gFe----------16gO
100----------------a---------------------b
a=100.56:72=77,7 la suta Fe
b=100.16:72=22,3 la suta O