Question

Find the empirical formula of iron oxide which has 69.9% of Fe and 30% of oxygen by mass.

Answer 1

Hint: For determining empirical formula:
Start with the number of grams of each element, given in the problem.
-If percentages are given, assume that the total mass is 100 grams so that
the mass of each element = the percent given.
-Convert the mass of each element to moles using the molar mass from the periodic table.
-Divide each mole value by the smallest number of moles calculated.
-Round to the nearest whole number. This is the mole ratio of the elements and is
represented by subscripts in the empirical formula.

Complete step by step solution:
We have been provided with 69.9% of Fe and 30% of oxygen by mass,
We need to find the empirical formula of iron oxide,
So, for that:
The empirical formula of a chemical compound is the simplest positive integer ratio of atoms present in a compound,
So, now as we have been given:
The iron oxide has 69.9% iron and 30.1% dioxygen by mass.
Thus, 100 g of iron oxide contains 69.9 g iron and 30.1 g oxygen.
Now, we will be finding the number of moles of iron and oxygen,
The number of moles of iron present in 100 g of iron oxide are: $\dfrac {69.9} {55.8} =1.25$
The number of moles of oxygen present in 100 g of iron oxide are: $\dfrac {30.1}{32} =0.94$
After finding the number of moles, we will be calculating the ratio of the number of carbon atoms present in one formula unit of iron oxide,
So, the ratio would be: $\dfrac {2\times 0.94} {1.25} =1.5:1$,
So, the number of moles, we will be calculating the ratio of the number of carbon atoms present in one formula unit of iron oxide comes out to be: 3:2,

So, we can conclude that the empirical formula would be: $F{{e}_ {2}} {{O}_ {3}} $.

Note: Chemical formulas tell us how many atoms of each element are in a compound, and empirical formulas tell you the simplest or most reduced ratio of elements in a compound. If a compound's chemical formula cannot be reduced any more, then the empirical formula is the same as the chemical formula.