Chemical Quantities - The Mole.

Empirical Formula of a Compound Lab

In this lab you will determine the empirical formula of the compound magnesium oxide. The compound will be made by burning magnesium ribbon in air.

Before you come into lab:

  1. Write an introduction/background. Be thorough and follow everything from the lab writeup handout. When you discuss the problem to be investigated, be sure to state what information will be needed in order to determine the empirical formula. Also include any definitions you may think are relevant. This should be written in paragraph form in complete sentences.
  2. Write a hypothesis.
  3. Write the materials and procedure in your own words (or copy mine).
  4. Make up a data table.

Materials:
ring stand, ring, clay triangle, Bunsen burner, crucible with lid, tongs, magnesium ribbon, balance, goggles.

Procedure:

  1. Set up the ring stand with the ring. Place the clay triangle on the ring. Place the burner under the clay triangle.
  2. Clean a crucible and lid with water. Heat them to dry, then continue heating for 5 minutes. Allow to cool for 5 minutes. For the rest of the lab, use the tongs to handle the crucible, do not touch with your hands.
  3. Mass the crucible and lid. Record.
  4. Place a coiled 25 cm length of magnesium ribbon in the crucible. Mass the crucible, lid, and Mg. Record.
  5. Do not look directly at the magnesium burning. Over a high flame, heat the uncovered crucible until the magnesium ignites. As soon as it is burning, place the cover over the crucible and remove the burner.
  6. After smoke production has ceased, replace the burner and continue heating the crucible. Every 2-3 minutes, carefully lift the lid and check the reaction. After heating a total of 10 minutes, check to see that the reaction is complete. The magnesium should be completely converted to a white/light grey powder. If ribbonlike material remains, continue heating until it is gone.
  7. Turn off the burner. Allow the crucible to cool completely (at least 7 minutes).
  8. Mass the crucible, lid and magnesium oxide. Record.
  9. The solid can be disposed of in the trash. Wash out the crucible and put away the materials.

Notes on the procedure: If the crucible lid is not put on right away when the magnesium starts to smoke, product can be lost. Also, if a green-yellow solid is forming, too high of a temperature is being used and magnesium nitride may be forming.

Data Analysis:
Calculate the empirical formula for magnesium oxide using your data. Show all work clearly.

Evaluation: as usual.
Conclusion: as usual.


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