Determining Empirical and Molecular Formulas

Empirical Formula

the simplest whole number ratio of atoms present in a compound.

Molecular Formula

a molecular formula shows all the numbers of each type of atom in a molecule

We are using _____ to help determine these formulas

Mass Percent Composition

Steps for Determining Empirical Formula

1. Simply turn the %’s into grams

2. Then turn the grams —→ Moles

3. Take the smallest moles answer and divide each of them by it

4. Round each answer to a whole number

5. Arrange accordingly

Steps for Determining Molecular Formula

1. Find the Molar Mass of the Empirical Formula

2. Divide that by the given Molar Mass

3. Use that answer to multiply each subscript of Empirical Formula

What is the empirical formula of a compound with 3.086% H, 31.61% P, and 65.31% O?

H₃PO₄

A compound containing nitrogen and oxygen is decomposed in the laboratory and produces 24.5 g N and 70.0 g O. Calculate the compound’s empirical formula.

NO₂

A compound sample contains 1.52 g N and 3.47 g O with a molar mass between 90 and 95 g. What is the molecular formula of this compound?

N₂O₄