Molecular Formula Determination

\[\begin{aligned} n &= \frac{MW_{compound}}{MW_{empirical}} \\ MF &= EF\times n \end{aligned}\]

Variables

nmolecular formula multiplier

MWcmolar mass of compound (g/mol)

MWemolar mass of empirical formula (g/mol)

Description

What is this formula?

This formula determines the integer multiplier used to convert an empirical formula into a molecular formula.

When to use it

Use this formula when the empirical formula is known and the molar mass of the compound has been measured experimentally.

Example

Given:

Empirical formula = CH2

Empirical formula molar mass = 14.03 g/mol

Measured compound molar mass = 84.18 g/mol

Formula:

n = MWcompound / MWempirical

Substitution:

n = 84.18 / 14.03

Result:

n = 6

Molecular formula:

(CH2)6 = C6H12

Applications

Elemental analysis

Organic chemistry

Inorganic chemistry

Analytical chemistry

Chemical education

Note

The molecular formula is obtained by multiplying every subscript in the empirical formula by the integer factor n. In theory, n should be a whole number. Small deviations from an integer may occur due to experimental uncertainty in molar mass measurements, in which case the nearest reasonable integer is usually selected.