Empirical Formulas

• Gives the lowest whole-number ratio of the elements in a compound.

• Example: Hydrogen Peroxide (H2O2)• Empirical Formula- HO

Steps

• Determine the number of moles for each element.

• Divide all elements by the smallest number of moles.

• You may need to multiply in order to get all elements in whole numbers.

Determining Empirical Formulas

• A compound is analyzed and found to contain 25.9% nitrogen and 74.1% oxygen. What is the empirical formula?

• Calculate the empirical formulas:

• 94.1% O, 5.9% H

• 67.6% Hg, 10.8% S, 21.6% O

Molecular Formulas• Can be a multiple of the empirical formula.• Example: H2O2 can be divided by 2 to become HO.

Finding Molecular Formula of a Compound

• Calculate the molecular formula of a compound whose molar mass is 60.0 g/mole and the empirical formula is CH4N.

• CH4N has a empirical formula mass of 30.0 g/mole.

• So 60.0 g/ 30.0 g = 2• Molecular formula = C2H8N2