PREPARATION AND CHEMICAL PROPERTIES OF OXYGEN
Introduction: Oxygen occurs in free state in the form of a diatomic species, O2.
Approximately, 1/5 of the earth's atmosphere is oxygen. Approximately, 89% of
the composition of water is oxygen. and 30% of earth's
crust by weight is oxygen. Therefore, we can draw the conclusion that oxygen is
a very important element in the free state or combined
chemically.
Oxygen can be produced in the laboratory by
1. the electrolysis
of water; 2H2O + (H2SO4 & Elect.)
-----------> 2H2 + O2
2. heating thermal
unstable metalic oxids;
2HgO + ∆----------> 2Hg + O2
3. peroxides
reacting with water; 2 Na2O2 + 2H2O + ∆-----------> 4 NaOH
+ O2
4. heating salts
that contain oxygen. 2KClO3 + (MnO2 + ∆) ---------> 2KCl + 3O2
In this experiment, oxygen will be prepared
by the decomposition of KClO3. KClO3 melts at 368.4oC.
It will decompose when the temperature is approximately 50oC above
its melting point (about 418oC). By adding the catalyst MnO2
to KClO3, the decomposition temperature is about 270oC.
Oxygen reacts with metals to form metallic
oxides, reacts with non-metals to form non-metallic oxides and oxidizes organic
and inorganic compounds.
2Ca + O2 ---------> 2CaO
CaO + H2O -------> Ca(OH)2
C + O2 ------------> CO2
CO2 + H2O -------->
H2CO3
S + O2 --------------> SO2
SO2 + H2O
----------> H2SO3
Procedure:
1. Preparation of oxygen by the decomposition
of KClO3.
Weigh 2.0 grams of MnO2 and
transfer to a crucible. Heat the crucible and MnO2 for several
minutes so that there are no combustible materials remaining in the MnO2.
Weigh 4.5 grams of KClO3 and transfer it to a large test tube.
Transfer the MnO2 to the same test tube and mix the two reagents.
Set up the apparatus.
Fill four 250 mL Erlenmeyer flasks with water
(no air bubbles) and place them in the pneumatic trough. Heat the test tube
with a low flame. While heating the test tube, wave the tube under the reaction
mixture. (When the reaction starts, it proceeds at a very rapid rate.) Collect
4 bottles of oxygen. With the aid of a glass plate, remove the bottles of
oxygen from the pneumatic trough and store upward.
Calculate the theoretical volume of oxygen
that should be produced at STP.
Chemical properties of oxygen:
A. Choose one bottle of oxygen and put a
glowing splint into the bottle of oxygen. Place the glass plate back on the
bottle immediately after dropping the splint into the bottle. Place 20 ml of
distilled water in the bottle and shake the mixture. Drop a piece of pH paper into
the bottle and determine the color and pH of the solution.
pH =
Write the chemical equation for this
procedure:
B. Place a small amount of sulfur (about the
size of a pea) in a clean deflagrating spoon. Place the spoon and sulfur over a
flame and ignite the sulfur (the color of burning sulfur is blue). Place the
burning sulfur in a bottle of oxygen. Place the glass place immediately on top
of the bottle. After the sulfur ceases to burn, remove the spoon and place 20
ml of water in the bottle. Shake the bottle and add a piece of pH paper to the
mixture. Determine the pH of the solution.
pH =
Write all chemical equations that has taken
place during this procedure.
C. Obtain a strip of magnesium ribbon about 2
inches long. Hold the strip with tongs and ignite the strip with the burner.
After ignition, place the strip in a bottle of oxygen (do not allow the burning
magnesium to touch the bottle). Place 20 ml of water in the bottle and shake
the mixture. Add a piece of pH paper to the mixture and determine the pH of the
solution.
pH =
Write all the chemical equations that have
taken place.
D. To the fourth bottle of oxygen add enough
distilled water to cover the bottom of the bottle. Hold a piece of steel wool with
tongs and ignite it with the burner. After ignition of the steel wool quickly
drop it into the bottle. Shake the mixture and add a piece of pH paper and
record the pH.
pH:
Write the equation for this reaction.