a. transform raportul masic in raport molar
nFe:nO=21/56 :8/16
= 0,375:0,5......IMPART prin cel mai mic
= 1: 1,33
formula compusului: (FeO1,33)n
masa lui molara : nx(56gFe+1,33x16gO)=232g------n=3----> Fe3O4
b. n(niu)Fe3O4= 116g/232g/mol= 0,5mol
deduc moli Fe si moli O2 din care se obtin 0,5mol compus
3mol 2mol,,,,,,.......1mol
3Fe + 2O2-------->Fe3O4
1,5mol....1mol.........0,5mol
m,Fe = 1,5molx 56g/mol=.........................calculeaza!!!!
c. 232gFe3O4.........64gO
100g........................x....................calculeaza !!!!