Lab 21
Date:
Combination Rxn of MgO
Objective 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
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
(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.
2.
3.
4.
5.
6.
Calculate the mass of the Mg that you began with.
Calculate the mass of the oxidized Mg that you produced.
Calculate the mass of the oxygen that combined with the Mg.
Convert the mass of the Mg into moles.
Convert the mass of the oxygen into moles.
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 –
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.