The molecular formula and empirical formula of a compound are related by a simple whole number multiple.
Understanding Empirical and Molecular Formulas
Before exploring their relationship, let's define each term:
- Empirical Formula: This formula shows the simplest whole number ratio of atoms in a compound. It is the most reduced form of a chemical formula.
- Molecular Formula: This formula indicates the exact number of each type of atom present in a molecule of the compound.
The Relationship
The key relationship is: Molecular Formula = n × Empirical Formula, where 'n' is a whole number. This means that the molecular formula is always a multiple of the empirical formula. The reference states this general relation: (Molecular Formula = n × Empirical Formula).
Explanation
- 'n' Value: The 'n' value represents how many times the empirical formula unit is repeated to form the actual molecular formula. If n = 1, the empirical and molecular formulas are the same.
- Finding 'n': You can find 'n' by dividing the molar mass of the molecular formula by the molar mass of the empirical formula.
n = (Molar mass of Molecular formula) / (Molar mass of Empirical formula)- Practical Insights:
- The empirical formula is often derived from experimental data, such as elemental analysis.
- The molecular formula is needed to understand the actual number of atoms in a single molecule of the compound.
Table of Examples
| Compound | Molecular Formula | Empirical Formula | n |
|---|---|---|---|
| Water | H₂O | H₂O | 1 |
| Hydrogen Peroxide | H₂O₂ | HO | 2 |
| Glucose | C₆H₁₂O₆ | CH₂O | 6 |
| Benzene | C₆H₆ | CH | 6 |
Points to Remember
- The empirical formula is always the simplest ratio.
- The molecular formula gives the actual number of atoms.
- The 'n' factor can be any whole number (1, 2, 3, etc).
- The empirical and molecular formulas might be the same.
Conclusion
In essence, the molecular formula shows how many atoms exist in one molecule, and the empirical formula presents the simplest ratio between these atoms. The molecular formula can be derived from the empirical formula if the molar mass of the compound is known through the relationship (Molecular Formula = n × Empirical Formula).
