A sample of oxide iron weighing 2.40g was heated in a stream of hydrogen until it was completely converted to the metal. If the metal weighed 1.68g. What is the formula of the iron oxide? (Fe=56, O=16)

Fe₂O₃

Explanation:

To solve this question we must find the moles of Iron in 1.68g. With the difference of the masses we can find the moles of oxygen. The formula will be obtained with the ratio of both amount of moles:

Moles Fe:

1.68g * (1mol / 56g)  =0.03moles

Moles O:

2.40g-1.68g = 0.72g * (1mol/16g) = 0.045moles

The ratio O/Fe is:

0.045moles / 0.03moles = 1.5 moles. this ratio is obtained if the formula is:

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