PREPARATION AND PROPERTIES OF OXYGEN
The objectives of this experiment are to
prepare, collect and investigate the properties of oxygen gas.
This experiment is appropriate for a
general or first-year college-prep course. Many common household bleaches
contain oxygen in the form of sodium hypochlorite, NaClO. If the hypochlorite
ion, ClO-, is decomposed, oxygen gas can be produced. In this experiment,
cobalt(II) chloride, a catalyst, will be used to increase the rate of production
of oxygen. The properties of oxygen will then be investigated.
Two lab periods.
Modifications / Substitutions.
Chlorine bleach has a strong odor and
should be handled carefully. Never mix ammonia with chlorine bleach; chlorine,
which causes severe lung damage is produced. Avoid breathing the sulfur dioxide
produced when sulfur burns; it is poisonous. Do not look at burning magnesium;
retinal damage may result. Goggles must be worn throughout the experiment.
- cobalt(II) chloride
- distilled or deionized water
- chlorine bleach
- steel wool
- one hole stopper
- 250-mL Erlenmeyer flask
- Bunsen burner
- utility clamp
- pneumatic trough
- eye dropper
- rubber tubing
- litmus paper
- small gas collecting bottles
- glass plates
- deflagrating spoon
- Magnesium sparklers such as those used on the Fourth of July may be used in
place of magnesium ribbon.
- Charcoal is available in a variety of forms. Old fashioned stick charcoal
- Sulfur is available from garden supply stores in products such as Ortho's "Flotex".
- A 12-oz soda bottle may be substituted for the Erlenmeyer flask.
- Any type of fairly deep tray or pan can be used in place of a pneumatic
- Baby food jars and their lids may be substituted for the gas collecting
bottles and the glass plates.
- An old bent spoon or piece of bent copper foil can be used in place of the
- If cobalt(II) chloride is not available or too expensive, an alternate
reaction can be carried out in which 3 or 6% hydrogen peroxide, H202, is used in
place of bleach and allowed to react with controlled amounts of the dark royal
blue copper amine complex, Cu(NH3)62+. The 3% hydrogen peroxide is available
from grocery or drug stores, while 6% hydrogen peroxide can be obtained from
drug or beauty supply stores under the brand name "Clairoxide." The
copper complex can be prepared by mixing an ammonia solution (household ammonia
works fine) with 25 mL of 0.1 M copper(II) sulfate (available under the name "Rooteater"
from a garden supply store) until the copper hydroxide precipitate dissolves,
leaving the transparent, dark blue amine complex ion. If this alternate
preparation is used, a two-hole stopper should be substituted for the one-hole
stopper in the flask. The copper amine complex is added to the hydrogen peroxide
from an eye dropper inserted in the second hole in the stopper. A trial run
should be done by the teacher to determine the amounts of copper amine complex
and hydrogen peroxide necessary to fill the five jars with oxygen.
- Clamp the neck of a 250-mL Erlenmeyer flask to a ringstand. This will
prevent it from tipping over.
- Insert the glass tube from an eye dropper in a one-hole stopper that fits
the flask and attach a 0.5-m piece of rubber tubing.
- Fill five gas collecting bottles to the very top with water; cover with
glass plates. Fill the trough 1/4 full of water, and invert the bottles of water
into the water. Carefully remove the glass plates, keeping the mouth of the
bottle below the water level in the tray.
- Put 150 mL of bleach into the Erlenmeyer flask.
- Measure out approximately 4 grams of cobalt(II) chloride. Crush any chunks.
- When all is ready, add the cobalt(II) chloride to the flask and quickly
insert the stopper/hose assembly into the bottle's mouth. Lead the rubber hose
from the generator into the tray of water and allow bubbles to escape for a
short time to purge the system of air.
- Insert the end of the rubber hose under the mouth of one of the bottles of
water. As the oxygen bubbles from the hose, it will displace the water from the
bottle. When one bottle is full of oxygen, move the hose to one of the remaining
- Lift each bottle of oxygen just enough to slip a glass plate over the
mouth. Do not lift the bottle completely out of the water while this is being
done. Once the glass plate is over the mouth of the bottle, the bottle can be
removed from the trough.
- If the reaction stops or slows, swirl the contents of the flask to mix the
reactants. When this no longer works, measure another 50 mL of bleach, quickly
remove the stopper and add it to the generator. For steps 10-15 an observation
table should be prepared.
- Light a candle. Remove the plate from one inverted bottle of oxygen just
enough to let out any water. Then hold the inverted bottle over a burning candle
and remove the glass plate. Observe the flame of the candle.
- With forceps hold a small tuft of steel wool in the flame of a Bunsen
burner for a few seconds. As soon as it begins to glow red, quickly remove the
cover from a second upright bottle of oxygen and hold the hot steel wool in the
oxygen gas. While holding the steel wool, use the glass plate to close off as much of the mouth of the bottle as possible. You want to collect any products
from the reaction between the oxygen and steel wool. Observe the steel wool.
When the reaction stops add 10 mL of distilled water to the bottle, replace the
glass plate and shake up the water and collected gas.
- In a similar fashion, heat the magnesium in the flame. When the magnesium
begins to burn, test it in a similar fashion as that used with the steel wool.
Don't forget to add the distilled water before shaking.
- Repeat step 11 with a small piece of charcoal.
- Use a deflagration spoon to test the reaction of burning sulfur in oxygen.
Put a small piece of sulfur about the size of a pea on the spoon. Hold the
Bunsen burner soon as the sulfur begins burning, hold the spoon in a bottle of
oxygen, and cover the mouth of the bottle as much as possible with a glass
plate. When the reaction is over, add the distilled water, replace the plate and
- Test the water in each of the bottles with litmus paper, and record your
Decant all solids and place in chemical
waste receptacle. The remaining liquid waste may be flushed down the drain with
copious quantities of water.
This experiment is a variation of
the preparation of oxygen used in kinetic studies. The reaction for the
- What physical properties must oxygen gas possess to allow it to be
collected by water displacement instead of air displacement? (Remember ALL gases
are less dense than water.) Would this method of gas collection be good for
collecting ammonia gas too?
- What physical and chemical properties of oxygen were illustrated in step 10
when the oxygen-was poured over the candle?
- Write a balanced equation for each burning reaction which occurred in steps
11-14. Write a second balanced equation for those reactions with water which
produced a color change in litmus paper.
- Give a reason for the difference between how things burned in the air
compared to how they burned in oxygen.
- Compare the litmus paper results in steps 11 through 14. Suggest a reason
why the results may have been the same or different.
- Suggest how you can "predict" the litmus paper results based upon
the substance you heat in the Bunsen burner.
2 NaOCl (aq) ----> 2 NaCl (aq) + O2 (g)
Other reactions for this
experiment are listed in order below.
4 Fe (s) + 3 O2 (g) ----> 2 Fe2O3 (s)
2 Mg (s) + O2 (g) ----> 2 MgO (s)
C (s) + O2 (g) ----> CO2 (g)
S (s) + O2 (g) ---->
Alyea, H.N. and Dutton, F.B., Tested
Demonstrations in Chemistry, American Chemical Society, Washington, 1960
pp. 7, 87, 91. -- Experiments using oxygen are described.
- If the magnesium oxide produced by the burning of magnesium ribbon proves
to be insoluble in water, suggest that students transfer the mixture to a test
tube and warm gently before testing with litmus paper.
- Do not use activated charcoal. After heating, it produces very little
change when held in the oxygen gas.
- The z-shaped spoons used to burn sulfur should be made up ahead of time and
tested to be certain they'll fit easily into the gas collection jars. If old
spoons are not available, a piece of copper foil or light gauge copper metal can
be bent into a spoon shape and used.
- The experiment should not be done with more than the 150 mL of bleach
called for or the reaction may force black cobalt oxide into the delivery tube
and into the collection bottles.
Joseph, A., Bandwein,
P.F., Marhott, E., Pollack, J.F., Castka, J.F., A Sourcebook for the
Physical Sciences, Harcourt, Brace and World, Inc., New York, 1961, pp.
32, 136, 150. -- The preparation of oxygen from hypochlorite and hydrogen peroxide
Summerlin, L.R., Chemistry of Common Substances, Silver Burdett Co., New York, 1979, p. 25. -- Describes experiments with oxygen.
Metcalfe, H.C., Williams, J.E., and Castka, J.F., Modern Chemistry,
Holt, Rinehart, and Winston Publishers, New York, 1982, p. 185. -- This work
describes the chemistry of oxygen.
Woodrow Wilson Leadership Program in Chemistry
The Woodrow Wilson National Fellowship Foundation
CN 5281, Princeton NJ 08543-5281