Determine the chemical formula of magnesium oxide

1
Lab18 Date Combination Rxn of MgO
Purpose -
Determine the chemical formula of magnesium oxide
Experiment -
(M1) Mass of empty crucible lid _______ g
Sand off a 10 strip of Mg, wind into a loose
coil. Place in crucible.
(M2) Mass of crucible lid Mg coil ____ g
Heat crucible with lid ajar
2
When Mg burns, cover crucible. Lift and close
lid every few seconds until Mg no longer burns
when lid is lifted.
Heat crucible with lid ajar for about 5 minutes
Let the crucible cool.
When cooled, slowly add 10 drops of pure water to
Mg, note smell.
Heat crucible strongly with lid off for about 5
minutes
Let the crucible cool.
(M3) Mass of crucible lid oxidized Mg ____ g
3
(M1) Mass of empty empty crucible w/ lid
_______ g
(M2) Mass of crucible, lid Mg coil ____ g
(M3) Mass of crucible, lid oxidized Mg ____ g
Analysis

1. Calculate the mass of the Mg that you began with.
2. Calculate the mass of the oxidized Mg that you
   produced.
3. Calculate the mass of the oxygen that combined
   with the Mg.
4. Convert the mass of the Mg into moles.
5. Convert the mass of the oxygen into moles.
6. Are there more moles of Mg or oxygen? By how
   many times? Round to the nearest whole number.
7. What is the chemical formula for magnesium oxide?
   Explain how you know.

Results
4
Skipped these in 2011-2012
Questions
1. Nitrogen gas is also present in the atmosphere
and it reacted with the Mg to magnesium nitride.
Write a balanced chemical equation for this
reaction. 2. When you added water to the
crucible. The water reacts with the magnesium
nitride (as heat is applied) to form magnesium
hydroxide and ammonia gas (NH3). You should have
smelled this ammonia when you added water. Write
a balanced chemical equation for this
reaction. 3. The magnesium hydroxide is
decomposed to magnesium oxide and water by
further heating. Write a balanced chemical
equation for this reaction.