LAB 8,
FORMULA OF AN OXIDE OF
MAGNESIUM
x Mg(s) + 1/2y O2(g)  MgxOy(s)
The 20 cm. piece of
lustrous metallic metal
you used as a reactant
in the beginning.
Molecular oxygen
from the atmosphere
is your gain of mass.
The white/grey powder
that exists as your
product in the crucible
at the end of the lab.
INTRODUCTION:
In this lab you will react metallic Mgo metal with molecular oxygen in the air. It is
important to remember that atmospheric oxygen is a diatomic molecule, while oxygen in
compounds is evaluated as individual atoms. Therefore the ratio of O 2 as a molecular gas to O
atoms in compounds is usually 1:2 or ½:1. In this lab the magnesium will bond to the oxygen,
which effectively fixes the oxygen in the solid product, which can be massed. Pleas consider the
following parameters of this lab:
A) The reaction is a REDOX, the Mg is oxidized and the oxygen is reduced.
B) The reaction is a synthesis, two elements are combining to form a
compound. The general formula is A + B  AB.
C) Oxygen as O2(g) can exist as a gas because it is non-polar and has weak
attractions.
D) Mg(s) is a metallic substance, which explains its luster and softness.
The results will yield the mass of Mg used and the mass of oxygen that reacted with it.
Both quantities can be converted to moles and the mole ratio can be calculated to give
the empirical formula.
MATERIALS:
1)
2)
3)
4)
5)
A 20-25 cm. strip of Mg metal.
A crucible and cover that fits/
A ceramic crucible triangle to hold the crucible on the ring stand.
Small ring and ring stand, Bunsen burner and lighter.
Spatula, balance.
SAFETY:
1) Use tongs to manipulate the crucible, do not get into the habit of
touching it as this may lead to burns.
2) If your crucible falls off of the ceramic triangle, let it fall to avoid
suffering any burns.
3) The magnesium metal may ignite and burn (sorry, it will not
explode). DO NOT LOOK AT IT as the flame is bright enough to
hurt your eyes. Call your teacher and remove the burner.
4) Wear goggles and apron, DO NOT SIT, stools under table.
PROCEDURE:
1) Obtain a piece of solid Mg of about 15 cm. and record the length in your
lab journal. Scrape the strip with a spatula to the point that it is shiny
(lustrous) and coil it as your teacher shows you..
2) Mass a clean dry crucible, place the Mg from step one into it and weigh
it again, record the combined mass of the crucible with the Mg metal. Be
certain that the coil of Mg is seated on the bottom of the crucible.
3) WITH THE CRUCIBLE COVER COMPLETLEY ON begin to heat the
crucible for about two min.. IF THE Mg IGNITES, REMOVE THE
BURNER (which should allow the flame to stop) , DO NOT LOOK
AT THE FLAMES. Continue to heat after the flame is extinguished for
about three min.
4) With the cover partially off heat the reaction for about two min., cool the
crucible for one min and add two drops of water, This will remove any
nitrogen compounds (nitriles) from your product.
5) With the cover off, heat to constant mass recording all masses in your
journal.
6) Clean up well.
DATA and QUESTIONS.
1) Write the oxidation states of Mg and oxygen both before and after
reaction.
2) Express the Mg in both grams and moles.
3) Express the oxygen in both grams and moles.
4) What is the ratio of Mg and oxygen (as O).
5) What is the empirical formula YOU calculate.
Caiafa 12/04