Empirical & Molecular formula

Calculating The Empirical and Molecular Formula

-Scientists use two kind of formula: molecular and empirical

 

Empirical Formula VS Molecular Formula

-Empirical formula of compound gives the lowest –term ratio of atom OR moles in the formula. All formula of Ionic compounds are empirical formulas.

-Molecular formula of a compound gives all atoms which make up a molecule. It is the formula of the ionic or covalent compound.

Examples

-Molecular Formula: C₆H₁₂O₆

-Empirical Formula:  CH₂O

- Molecular Formula:  Na₂C₂O₄

- Empirical Formula:  NaCO₂

Formula and Molecular Formula Converting between Empirical

- Molecular Formula = Empirical Formula x Whole number

- Molecular Formula Mass = Empirical Formula x Whole number

-Mass of one Mole = Empirical Formula Mass (in grams) x Whole number

Example

Find the molecular formula of a liquid with an empirical formula C₅H₁₂ and mass of one mole is 144.0g?

Step1: Calculate the empirical mass in grams of C₅H₁₂.

            5 x 12.0g + 12 x 1.0g =72.0g/mol

Step2: Since mass of 1 mole = empirical formula mass x Whole number

           144g / 72.0g=2

Answer: (C₅H₁₂) x 2 = C₁₀H₂₄