Question

determine the molecular formula of an oxide of iron is which the mass percent of iron and oxygen are 69.9 and 30.1 given that molecular mass of the oxide is 159.8g.molecule9
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Answer 1

Given :

• % Fe = 69.9

• % O = 30.1

• Atomic mass of Fe = 55.8 g

• Atomic mass of O = 16 g

Solution :-

Relative no of atoms

We need to divide the % composition of the elements with their  atomic masses

➝ F = 69.9 / 55.8 = 1.25

➝ O = 30.1 / 16  = 1.875

Simple ratio

Divide all the values obtained with the least value (i.e. 1.25 ) in this case

➝ 1.25 / 1.25  :  1.875 / 1.25

➝ 1 : 1.5

➝ 2 : 3

➽ Empirical formula = Fe2O3

➽ Empirical mass = 2 Fe + 3 O = 2 x 56 + 3 x 16= 112 + 48 = 160 g

➽ Molecular mass = 160 g

➽ Molecular mass = Empirical mass

∴ Molecular formula = Empirical formula

The molecular formula of the compound is Fe2O3