Question

Iron can form three different oxides, FeO,Fe2O3 and Fe3O4. A sample of iron oxide was analyzed and was found to contain 69.943% iron with the rest of the mass from oxygen. Determine the empirical formula to determine the identity of the iron oxide

Answer 1

The empirical formula of the iron oxide is $Fe_2O_3$.

And the empirical formula is in an agreement with $Fe_2O_3$ that is iron(III) oxide.

Given:

A sample of iron oxide with 69.943 % of iron and rest with of the mass from oxygen.

To find:

The empirical formula of iron oxide & to identify the type of iron oxide.

Solution:

Consider in 100 grams iron oxide has 69.943 % of iron.

Percentage of oxygen in 100 grams of iron oxide :

= 100% - 69.943%=30.054%

• Mass of iron in 100 grams sample =$100g\times \frac{69.943 }{100}=69.943 g$
• Mass of oxygen in 100 grams = $100 g\times \frac{30.054}{100}=30.054 g$
• Moles of iron = $\frac{69.943 g}{55.845 g/mol}=1.2524mol$
• Moles of oxygen = $\frac{30.054 g}{15.999 g/mol}=1.8785 mol$

Let the empirical formula of iron oxide be $Fe_xO_y$

For empirical formula divide all moles of elements with the least value of moles of an element in the compound:

$x=\frac{1.2524mol}{1.2524mol}=1\\\\y=\frac{1.8785 mol}{1.2524mol}=1.5\\\\Fe_xO_y=Fe_1O_{1.5}\\\\=Fe_{10}O_{15}=Fe_2O_3$

The empirical formula of the iron oxide is $Fe_2O_3$.

And the empirical formula is in an agreement with $Fe_2O_3$ that is iron(III) oxide.

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