Chemical quantities (AS)

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If you heat 3.970 g of a mixture of Fe₃O₄ and FeO to form 4.195 g of Fe₂O₃, what is the mass percent of FeO originally in the mixture?
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Corrie writes .....
 
Let's assume you have Z g of FeO in your mixture to start with. This means you have (3.970 - Z) g of Fe₃O₄ in the mixture.
 
The fraction of Fe in FeO is [56/(56 + 16)].
The mass of Fe in Z g FeO is therefore [56/(56 + 16)] x Z g.
 
The fraction of Fe of Fe in the Fe₃O₄ is (3 x 56)/[(3 x 56) + (4 x 16)].
 
Thus the mass of iron in the Fe₃O₄ is
 
= (3.970 - Z) x (3 x 56)/[(3 x 56) + (4 x 16)]
 
Add these two masses together to obtain the total mass of Fe in the mixture, in terms of the unknown Z.
 
Similarly, the mass of Fe in 4.195 g of Fe₂O₃ will be 4.195 x (2 x 56)/[(2 x 56) + (3 x 16)]
 
Work out this mass. It is equal to the total mass of Fe in the mixture above. Solve for Z to find the mass of FeO in the mixture.
 
Hope this helps? If not, come back to us via Re:act, not email, please.
 

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updated: 26 March 2008