Making Ionic Compounds

Background:

Elements combine to form compounds in order to become more stable.  Ionic compounds are formed from the attraction between positive and negative ions.  Ions are formed when atoms gain or lose electrons.  If energy is released as the compound is formed, the resulting product is more stable than the reacting elements.  How can you tell a reaction releases energy?  What observations should you be able to make?  What element is necessary for something to burn?  What are the two major elements that make up the air we breathe?  Think about these questions as you continue to read this lab.

Objective:

You will react elements to form two compounds.  You will test the compounds to determine its properties.  In this lab, you will actually be MAKING two ionic compound using magnesium. You will determine those characteristics which make an ionic compound quite different from a covalent compound.

Materials:

• magnesium metal (in ribbon form)
• crucible
• crucible tongs
• ring stand and wire mesh
• Bunsen burner AND Fisher burner
• stirring rod
• triple beam balance
• 100 mL beaker
• 50 mL graduated cylinder
• wash bottles with distilled water
• conductivity tester (one for the whole class)

Procedure:

DO NOT LOOK DIRECTLY AT THE BURNING MAGNESIUM

IT WILL PERMANENTLY DAMAGE YOUR EYES.

1. You will use TWO burner setups at the same time: One using a Fisher burner and another using the bunsen burner.  (Use both gas outlets at your bench.)
2. Set up the ring stand and wire mesh so that is is no more than 2" above the Fisher burner top.
3. Measure the mass of a clean, dry crucible and record the mass in the data table.
4. Roll approximately 10-12 cm of the magnesium ribbon around your finger so it forms a loose coil.
5. Place the rolled magnesium into the crucible and measure the new mass of the crucible plus magnesium. Record in data table.
6. Place the crucible (by itself) on the wire mesh and heat up the crucible using the Fisher burner.  Heat 6 minutes. The crucible will get VERY, VERY hot.
7. Light the bunsen burner and adjust so that it has a very short blue cone (1.5" tall).
8. Drop the coil of magnesium into the hot crucible. 
9. Turn the lit bunsen burner over into the crucible to light the magnesium making sure that the tip of the inner blue cone comes in contact with the magnesium.
10. When the magnesium metal catches fire, turn off the gas of the BUNSEN burner.  Keep the FISHER burner going underneath the crucible until the reaction is complete (about 30 seconds or so).  Then, turn off the gas to the Fisher burner.
11. Your crucible should now contain an ash.  Let cool completely.
12. Measure the mass of the crucible plus product.  Record on data table.
13. Take a dry glass stirring rod and "crush up" the ash in the crucible.  Be sure to look VERY CAREFULLY AT THE COLOR(S) of the ash.  What color(s) do you see?  Record your observations in the data table.
14. Was the reaction endothermic or exothermic?  (If you don't know what these words mean, google them.) Record on data table.
15. Carefully pour out the ash product into the beaker.
16. Add 40 mL of distilled water to the product in the beaker.
17. Stir with stirring rod until dissolved.
18. Take the beaker with your ash solution to your teacher.  You will check the mixture with a conductivity tester and record your results on the data table.
19. Dump out the solution into the TRASH.
20. Thoroughly rinse out the crucible and return to the teacher.
21. Return all other tools CLEAN and put away.

Data Table:

Print off the data table here.

Analysis:

Answer the questions on the data table.