The moles of Al that are needed to react completely with 17 .5 moles of FeO is 11.67 moles
calculation
2Al +3 FeO → 3 Fe + Al₂O₃
The moles of Al is calculate using the mole ratio
That is; From equation above the mole ratio of Al :FeO is 2:3 therefore the moles of Al
= 17.5 moles x 2/3 = 11.67 moles
