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Determine the molecular formula of an …

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Determine the molecular formula of an oxide of iron,in which the mass per cent of iron and oxygen are 69.9 and 30.1, respectively
  • 1 answers

Gaurav Seth 5 years, 1 month ago

We have given,

Mass percent of iron (Fe) =69.9%

Mass percent of oxygen (O)=30.1%

Number of moles of iron present in the oxide =69.90/55.85 =1.25

Number of moles of oxygen present in the oxide=30.1/16.0

=1.88

Ratio of iron to oxygen in the oxide,

1.25:1.88

=1:1.5

=2:3

Therefore the empirical formula of the oxide is Fe2O3.

Empirical formula mass of Fe2O3= [2(55.85) +3(16)]g

Molar mass of Fe2O3=159.69g

Thus, n= Molar mass/Empirical Formula mass =159.69/159.7g

 =0.999 = 1(approx.)

Molecular formula of a compound is obtained by multiplying the empirical formula with n. Thus, the empirical formula of the given oxide is Fe2O3 and n is 1.

Hence, the molecular formula of the oxide is Fe2O3.

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