Experiment 3 Determining an Empirical Formula IUG, 2019

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

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.

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

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)

PROCEDURE 1-weight the empty crucible. 2- weight of crucible and magnesium. (Mg metal about 0.1-0.2g) 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 .

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 (%) ____________