CBSE Class 11-science Answered

Let us consider weight of FeO & Fe₃O₄ be 'a' & 'b' gm respectively. 

Consider the following reactions.

2 FeO + 1/2 O₂ ------> Fe₂O₃ 

Fe₃O₄ + 1/2 O₂ ------> 3Fe₂O₃ 

Molar mass of FeO =144 g and that of Fe₂O₃ is 160 gms. 

Thus 144 g FeO gives 160 g Fe₂O₃ 

'a' g FeO will give 160 x a/144 gm Fe₂O₃ --------------(1) 

Similarly, weight of Fe₂O₃ formed by ‘b’gm Fe₃O₄ = 160 x 3b/464 --------(2) 

Assuming total weight i.e. (a+b) = 100. -------- (3) 

As there is an increase of 5 % we get, from eqn. 1,2 & 3 . 

(160 x a /144) +160 x 3b/464 = 105 

solving we get, 

a= 21.06 & b = 78.94 

Thus % of FeO = 21.06 % & that of Fe₃O₄ = 78.94 %