A mixture of FeO and Fe3O4 when heated in air to constant weight gains 5% in its weight. The % of FeO in the sample is

Asked by Anil | 19th May, 2017, 10:28: PM

Expert Answer:

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


Consider the following reactions.


2 FeO + 1/2 O2 ------> Fe2O


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 Fe2O


'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 %

Answered by Vaibhav Chavan | 20th May, 2017, 06:29: PM