1. Experiment 3 Determining an Empirical Formula
IUG, 2019

2. To determine the empirical formula of magnesium oxide .
OBJECTIVE
To determine the empirical formula of magnesium oxide .

3. Empirical formula Molecular formula
Which gives the smallest whole number ratio of atoms in a compound.
Molecular formula
Which gives the actual number of each type of atom in the compound.

4. The empirical formula of a compound can be determined either by
1-Decomposition reactions
2-Formation reactions

5. MgO(s) + H2O(l) → Mg(OH)2(s) (3)
When magnesium metal is heated in air, two chemical reactions occur simultaneously. A portion of the magnesium reacts with oxygen to form magnesium oxide and the other part of the magnesium reacts with nitrogen to form magnesium nitride.
Mg (s) + O2(g) → MgO(s) (1)
Mg(s) + N2(g) → Mg3N2(s) (2)
The mixture of these two compounds can be easily converted to relatively pure magnesium oxide by the following reactions:
MgO(s) + H2O(l) → Mg(OH)2(s) (3)
Mg3N2(s) + H2O(l) → Mg(OH)2(s) + NH3(g) (4)
Mg(OH)2(s) → MgO(s) + H2O(g) (5)

6. PROCEDURE
1-weight the empty crucible. 2- weight of crucible and magnesium. (Mg metal about g) 3-Heat with cover. 4-Heat with out cover (5 mins). 5-Add (5-7) drop water. 6-Heat for 10 mins. 7-Cooling. 8-Weight .

7. Results Determining Empirical Formula of Magnesium Oxide
(At.wt. Mg=24.3g/mol , At.wt. O =16g/mol )
1. Mass of empty, cooled crucible (g) ____________
2. Mass of crucible and magnesium (g) ____________
3. Mass of magnesium (g) ____________
4. Mass of crucible and magnesium oxide (g) ____________
5. Mass of magnesium oxide (g) [ step 4 – step 1 ] ____________
6. Mass of oxygen (g) [ step 5 – step 3 ] ____________
7. Moles of magnesium (mol) ____________
8. Moles of oxygen (mol) ____________
9. Mole ratio of magnesium to oxygen ____________
10. Empirical formula of magnesium oxide ____________
11. Percent Mg by mass in compound (%) ____________
12. Percent O by mass in compound (%) ____________