A mixture of FeO and `Fe_3O_4` when heated in air to a constant weight gains `5%` in its weigh. Find the composition of the initial mixture.

Explanation

Let the total mass of the mixture = 100g
Let the mass of FeO in the mixture be xg
Mass of `Fe_3O_4` will be (100-x)g
Both the oxides on heating will change to` Fe_2O_3 `on heating.
`underset(144g)2FeO + 1/2O_2rarrunderset(160g)Fe_2O_3`
xg of FeO on heating will produce `Fe_2O_3 = (160/144)xg`
`underset(464g)2Fe_3O_4 +1/2O_2 rarr underset(480g) 3Fe_2O_3`
(100-x)g of `Fe_3O_4` will produce `Fe_2O_3`= (480/464)xx(10-x)g`
Total mass of `Fe_2O_3` actually formed = 100+5 =105g
(160/144)xg+(480/464)`xx`(10-x)g=105g
x = 21g
`% `of FeO =21
`% `of `Fe_3O_4 = 79`