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Chemistry Lessons Review Links

Empirical Formula from Mass

This will guide you through determining the Empirical Formula a compound just based on the mass of its parts.

Empirical Formula: The simplest ratio of the atoms present in a molecule.

Problem: Find the empirical formula for the oxide that contains 42.05 g of nitrogen and 95.95 g of oxygen.


As with most stoichiometry problems, it is necessary to work in moles. The ratio of the moles of each element will provide the ratio of the atoms of each element.

  1. Convert the mass of each element to moles of each element using the atomic masses.

  2. Find the ratio or the moles of each element by dividing the number of moles of each by the smallest number of moles.

  3. Use the mole ratio to write the empirical formula.

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