Tutorials

Molecular Formula vs. Empirical Formula

Core Concepts

In this tutorial, you will learn about the differences between molecular and empirical formulas. You will also learn how to identify, and convert molecular formulas into empirical formulas through a series of examples.

Topics covered in other articles

Vocabulary

n-value: an integer that is multiplied by the empirical formula in order to obtain the molecular formula

molecule: A compound formed through the bonding of 2 or more atoms

Molecular vs Empirical Formula:

Molecular Formula

A molecular formula demonstrates the number of each atom present in a given molecule. Molecular formulas are able to describe a wide range of molecules, as they give no information about the structure.

The molecular formula, is the formula that is most commonly used in chemsitry.

Example:

C6H12O6 → The molecular formula used to describe fructose, glucose, and galactose.

N2O4→ The molecular formula used to describe nitrogen tetroxide.

C5H3N3→ The molecular formula used to describe cyanopyrazine.

Empirical Formula

The empirical formula demonstrates the simplified ratio of the number of atoms in a molecule. When doing an experiment, the empirical formula is typically obtained first. In order to determine the true number of each atom in a molecule, it is important to obtain an n-value. The n-value is an integer that is multiplied by the empirical formula in order to obtain the molecular formula. The molecular formula and empirical formula can at times be the same, as long as the ratio of atoms in the molecular formula is at its simplest.

The empirical formula is not used very often in chemistry. Generally, the molecular formula is used – and in most cases, they are the same.

Example:

CH2O→ The empirical formula of fructose, glucose, and galactose once reduced.

NO2→ The empirical formula of nitrogen tetroxide once reduced.

C5H3N3→ The empirical formula and molecular formula for cyanopyrazine are the same, as the ratio of the atoms cannot be simplified.

How to convert a molecular formula to an empirical formula:

  1. Let’s start with a compound, for example ethyl acetate: C4H8O2
  2. Find the greatest common factor (GCF) between the number of each atom. In this case, the GCF between 2,4, and 8 is 2 (2 is also the n-value, when multiplied by the empirical formula, the original molecular formula is obtained).
  3. Divide the number of each atom by the greatest common factor. In this case C= 4/2= 2 , H= 8/2= 4, O= 2/2= 1.
  4. Replace the previous values of each atom with the newly calculated ones. This would result in the empirical formula of C2H4O.

We hope you now understand an empirical formula vs molecular formula. Leave questions in the comments!

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