Question

A sample was analyzed and shown to have 63.52% iron and 36.48% sulphur. Determine the empirical formula.

Answer 1

Hint: The answer here is based on the concept of empirical formula calculation of a chemical compound where the molar mass of the compound is to be calculated and then the ratio of these will give the empirical formula.

Complete answer:
In the lower classes, we have studied the concepts of writing the chemical formula of a compound which also tells about the empirical formula calculation and related calculation which is related to this concept.
Let us now see this concept in detail and can deduce the required answer.
- Empirical formula in chemistry is defined as the simplest positive integer ratio of atoms present in a compound.
- Now, we are given the data where a sample is having 63.52% iron and sulphur which has 36.48% in composition.
Let us assume the sample to be of 100g which is an unknown sample.
We shall calculate the molar mass of the given substance individually.
For iron, molar mass = 55.845 g/mol
For sulphur, molar mass = 32.06 g/mol
Now, we shall calculate the total number of moles of each atom present in the sample.
For iron, $63.52g\times \dfrac{1}{55.845g/mol}\approx 1.137$ moles of $Fe$
For sulphur,$36.48g\times \dfrac{1}{32.06g/mol}\approx 1.138$ moles of $S$
Now, as the total number of moles of iron and sulphur are in the same ratio that is 1 : 1, the ratio of these elements are same and hence the empirical formula for the given data can be written as, $FeS$
Hence, the empirical formula is $FeS$

Note:
Note that empirical and molecular formulas are different terms where empirical formula shows the simplest whole number ratio of atoms in a compound whereas molecular formulas show the number of each type of atom in a molecule.