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In the previous blogpost, we have discussed on the Common Errors on Calculating Empirical Formula, when given Composition by Mass. Today we shall go one step further and see how we can determine the Molecular Formula from an Empirical Formula.

The Molecular Formula shows all the atoms of each element contained in one molecule.

Empirical Formula shows the simplest ratio of the different types of elements present in a molecule.

For example, Hexane has Molecular Formula of C₆H₁₂ and Empirical Formula of CH₂.

As such, Molecular Formula is a simple multiple of the Empirical Formula:

Molecular Formula = n X Empirical Formula

where n = 1, 2, 3, etc

The molecular formula can be calculated from:

1. Empirical Formula
   
2. Relative Molecular Mass, Mr of Compound

Let’s take a look at an example.

Example:

Glucose has empirical formula CH₂O and relative molecular mass of 180. Find the molecular formula of glucose.

(given: H = 1.0; C = 12.0; O = 16.0)

Suggested Answer:

Relative mass of Empirical Formula, CH₂O = 12 + 2(1) + 16 = 30

Relative molecular mass = n X relative mass of the empirical formula

thus, n = Relative molecular mass / relative mass of the empirical formula

= 180 / 30 = 6

Therefore, Molecular Formula of Glucose = 6 X CH₂O = C₆H₁₂O₆

PS: Let me know how you feel about this blogposts. Drop me a comment.

Related Articles:

• O Level Chemistry: Molecular & Empirical Formulae
• O Level Chemistry: Mole Concepts / Chemical Calculations
• O Level Chemistry: Types of Formula
• O Level Chemistry: Common Errors in Calculating Empirical Formula
• O Level Chemistry: Mole Concepts / Chemical Calculations