Experiment 1: Finding the Formula of a Compound for AP Chemistry

By — McGraw-Hill Professional
Updated on Feb 2, 2011

For a quick review on stoichiometry, refer to the following concepts:


The formula of a compound is determined by using the mass of the original substance, usually a metal, and the mass of a compound of that substance, usually an oxide.


      analytical balance
      crucible and cover
      support stand
      triangle crucible support

Experiment 1: Finding the Formula of a Compound


  1. the mass of the crucible and cover
  2. the mass of the original sample and the crucible and cover
  3. the mass of the reacted sample and the crucible and cover

The last measurement must be done after the sample has cooled to room temperature.


The mass of the sample is calculated by taking the difference between masses 1 and 2. The mass of the substance that combined with the original substance is calculated from the difference between masses 2 and 3. The moles of the substances must be calculated by dividing each mass by the molar mass of the substance. The empirical formula is calculated from the simplest ratio of the moles of the elements present.


This procedure will allow you to calculate the empirical formula of the substance. The experiment is often performed by reacting magnesium metal with atmospheric oxygen to form magnesium oxide.

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