Burning Mg Ribbon
Lab #5
Purpose:
To find the formula of magnesium oxide.
Materials:
Mg ribbon
Tongs
Burner
Crucible
Balance
Background:
When magnesium ribbon burns in the presence of oxygen a compound
called magnesium oxide is formed.
Prelab Question:
1. If you start with 3 grams of Mg, how many moles of Mg do you have?
Procedure:
Find the mass of a crucible and lid.
Find the mass of about 5 inches of Mg ribbon in the crucible with the
lid.
Use the Bunsen burner to heat the crucible for about 15 minutes or
however long it takes to turn the ribbon to ash. Cool for a minute then
add 3 mL of water to the ash. Heat the mixture for another five
minutes.
Allow to cool and find the mass of the magnesium ash, crucible and
lid.
Data:
1. Mass of crucible and lid
2. Mass of crucible, lid, and Mg before heating
3. Mass of crucible, lid, and Mg after heating
__________
__________
__________
Analysis:
Calculate the grams of Mg that you started with.
Calculate the grams of oxygen in the compound. You get this by
subtracting the (mass of crucible, lid, and Mg after heating) from (mass of
crucible, lid, and Mg before heating).
Calculate the moles of Mg.
Calculate the moles of Oxygen
Divide the moles of Oxygen by the moles of Magnesium to get the mole
ratio.
The mole ratio gives you the formula for the compound. What is the
formula for the compound?
Discussion:
What are some of the potential sources of error in this experiment? List at
least three.
Why was water added to the mixture?