Question

A sample weighing 3.193 g is a mixture of Fe2O3 (molar mass = 159.69) and Al2O3 (molar mass = 101.96). When heat and a stream of H2 gas is applied to the sample, the Fe2O3 reacts to form metallic Fe and H2O(g). The Al2O3 does not react. If the sample residue (the solid species remaining after the reaction) weighs 2.864 g, what is the mass fraction of Fe2O3 in the original sample?

Answer 1

Let the mass of Fe2O3 be x

​Therefore the reaction of Fe2O3 with H2

​Fe2O3 + 3H2 ---> 2Fe + 3H2O

​moles of Fe2O3 = x/159.69 now if y/159.69 moles react

​Fe2O3 mass = x-2y , Mass of Fe = 2y*63.5/159.69

Therefore we see from reaction one mole of Fe2O3 will produce 2 moles of Fe , since we know the solids present will be only Fe2O3 ,Fe, and Al2O3 so the 2.864 grams containing will be these three compounds

We now know the mass of all the three compounds We evaluate them

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