H2SO4(l)
+ HCOOH(l) 
CO(g) + H2SO4.H2O(l)
|
Experiments with Carbon Monoxide |
General Safety
Precautions.
Always
wear safety glasses. Gases in syringes may be under pressure and
could spray liquid chemicals. Follow the instructions and only use
the quantities suggested.
Toxicity.
Carbon
monoxide has a relatively high toxicity. The molecule binds to hemoglobin
about 300 times better than oxygen, thus disabling the ability of hemoglobin
to carry oxygen to tissues. Symptoms of carbon monoxide poisoning
include headache, mental dullness, weakness, nausea and vomiting.
If any of these symptoms are noted, seek fresh air. Recovery from
mild levels is rapid and complete with no cumulative effects. Higher
levels of exposure can lead to unconsciousness and death.
Chemical
Caution: Sulfuric Acid
Concentrated
sulfuric acid is an exceptionally dangerous chemical. The acid causes
severe chemical burns upon contact. If contact with the acid is suspected,
wash area with plenty of water. Contact with the eyes may cause permanent
damage and possible blindness. Wash the eyes with plenty of water
and seek immediate medical attention.
Suitability.
All of
these experiments are suited for use as classroom demonstrations.
The techniques described herein are more advanced than those used in the
first ten parts of this series. Individuals attempting these experiments
should be experienced with the simpler syringe/gas techniques. These
experiments are not generally advised for use as laboratory experiments
conducted by typical high school students. Advanced students or students
with special laboratory skills could be allowed to generate CO(g) by this
method under close supervision by the instructor.
Syringe Lubrication.
We recommend
lubricating the black rubber diaphragm of the plunger with silicone spray
(available from hardware stores) or medium-grade silicone oil (Fisher Catalog
Number S159-500; $34/500 mL.)
Equipment. (This equipment can be ordered from a variety of vendors including Educational Innovations, Flinn Scientific (US sales only), Micro Mole, and Fisher Scientific. Part numbers and links to their websites are provided.)
- several 60-mL plastic syringes with a LuerLOK fitting
- Latex LuerLOK syringe cap fittings
- Small plastic weighing boats
- balance capable of measuring to 0.01 g
- two pieces, latex tubing, 1/8-inch (3.175 mm) ID, 5 cm lengths
- two 18 x 150 mm test tubes
- two-hole #1 stopper fitted with two short lengths (2 cm) of glass tubing
- pinch clamp or hemostat
- ring stand and three suitable clamps to hold test tube and syringes
- small Bunsen burner
- matches or a lighter
- ‘permanent’ marker pen
Chemicals.
Carbon monoxide is produced by the Thermal Method. Theoretically, this mixture will produce over 100-mL CO(g) that is >95% pure. The production of CO is relatively fast and it typically takes 15 seconds to fill a syringe. Upon heating this mixture, CO(g) is produced according to the reaction:8 drops concentrated sulfuric acid 8 drops (0.23 g; 5 mmol) formic
H2SO4(l)
+ HCOOH(l)
CO(g) + H2SO4.H2O(l)
This method utilizes two clean, dry 60-mL syringes connected by latex tubing to a 120 x 15 mm test tube fitted with a suitable (#0) two-hole stopper. Short lengths of glass tubing are inserted through the rubber stopper. (CAUTION! Soak the rubber stopper in alcohol and lubricate the glass tubing with alcohol before inserting the tubing through the stopper. Hold glass tubing with a thick towel while inserting! Avoid puncture wounds! Do not force the glass!) Syringe plungers should move easily in barrels. This can be facilitated by applying a thin film of silicone oil to the plunger's rubber seal. The assembled apparatus is shown in Figure 1. Also needed is a small flame source such as a long-nosed butane lighter or an alcohol lamp. The left syringe, labeled 'CO' is used to collect relatively pure CO(g) and the syringe labeled 'Waste' is used to collect impure samples of gas and unwanted air. A pinch clamp or hemostat is used to pinch closed one of the latex tubes.
Place 8 drops of each concentrated sulfuric acid and formic acid in the test tube. The reaction will immediately commence forming small bubbles of CO(g). Insert the stopper firmly in order to form an air-tight seal. Hold the heat source with one hand while manipulating the tubing clamp or hemostat with the other. The 3-step maneuver is shown in Figure 2.
Figure 1. |
Method for generating CO(g). Notice that a simple long-nosed butane lighter is all that is needed to produce CO within seconds. |
 |
 |
 |
Replace the latex tube from the CO-filled syringe with a latex syringe cap. The CO-filled syringe is > 95% pure and ready for experiments. Allow the apparatus to cool. The plunger in the Waste syringe may move outward at first because gas generation may continue for several seconds after the test tube is removed from the flame. The plunger may move inward as the apparatus cools. Note: It is possible to generate multiple syringefuls of CO(g) by scaling up the amount of reagents used.
Washing the
gases.
It is
not necessary to wash CO(g).
Preparation
of Carbon Monoxide in the Microwave Oven.
Samples
of CO(g) also can be prepared conveniently in a microwave
oven.
Disposal.
Unwanted
samples of CO(g) including the contents of the Waste syringe can be discarded
in a fume hood or out of doors. The liquid remaining in the test
tube is partially hydrated H2SO4
which can be dissolved by adding about 10-mL water to the test tube and
discarded as acidic wastes. The test tubes can be reused unless they
have been damaged.
| Experiment 1. Blue Jets!
Combustion of CO(g) with a Blue Flame.
Equipment:
Fit a 15 cm piece of latex tubing into a pipet as shown in Figure 3. It should make a snug fit. Generate a syringeful of CO(g) as described above. Replace the syringe cap with the latex tube/glass pipet. |
Figure 3.
|
Part A. While holding the end of the pipet 2 - 3 cm from a candle flame, discharge 30 mL CO over a period of 10 seconds through the flame. A jet of blue fire should appear on the opposite side of the candle.
Part B. While holding the end of the pipet <1 cm from the flame, slowly discharge CO(g) near the flame in order to ignite the pipet tip. It will burn with a gentle blue flame which can be sustained by carefully discharging the CO at a slow rate.
Part C. Place a candle
in a large (> 1 L) vessel that can be sealed such as a pickle jar or a
desiccator. Light the candle and cover the vessel, creating a closed
system. Darken the room. The candle flame will diminish in
size and lose it's characteristic yellow color as the O2(g)
is depleted. As the flame becomes smaller, note the increased size
of the blue region especially near the lower part of the flame. The
blue color is attributed to the combustion of CO(g) which replaces CO2
as the dominant product of combustion and is itself combustible.
Experiment 2. Wimpy Soap
Bubble Explosions and Wimpy Rockets.
Equipment:
CO(g) + 1/2 O2(g)
CO2(g) DH
= -283.0 kJ
This mixture can be 'exploded':
(a) in the form of soap bubbles similar to Experiment 5 of the Oxygen
Chapter or (b) with the use of a piezoelectric igniter
as described in Experiment 6 of the Oxygen Chapter.
The 'explosions' are mild. The rocket, for example, produces a bright
flash of light but only travels a few dm. Other gas mixtures will
not leave the launcher but do produce a flash of light. Exploding
various gas mixtures such as C2H2/O2,
H2/O2, and CO/O2,
would provide a useful comparison and reveal the relative reactivities
of these gases. (See: General information on successfully filling
and launching rockets.) (See: Instructions for the assembly
of a piezoelectric sparking device — needed for launching the rockets.)
Experiment 3. Quantification
of Carbon Monoxide. Reaction with CuCl(aq).
Equipment:
CuCl(aq) + CO
Cu(CO)Cl(H2O)2
This reaction allows for the quantification of CO(g) in gas mixtures.
Cuprous Chloride Solution.
Prepare
a stock solution of 1.6 M CuCl(aq) in 3 M HCl. To prepare 100-mL
of the solution, prepare 100-mL of 3 M HCl by diluting 25-mL concentrated
HCl to 100-mL with distilled water. To this solution, dissolve 16-g
anhydrous cuprous chloride, CuCl. The solution will be deep forest
green in color. This solution will react with CO(g) in a 1:1 volume
ratio: 1-mL solution will react with 1-mL CO.
Part A. Quantification.
Prepare
a syringe filled with 30-mL pure CO(g). To this syringe suction in
30-mL 1.6 M CuCl(aq) solution. Attach the syringe cap and shake the
contents vigorously. Within 30 s the CO will have completely reacted
with the solution. Vigorous shaking is necessary because CO(g) is
nearly insoluble in water. The amount of gas that did not dissolve
in the solution represents gases other than CO. For quantification
purposes, record the volume of gas originally present by noting the position
of the plunger's rubber seal. Record the volume of gas again after
the reaction is over. The volume of CO(g) originally present is equal
to the difference in these two values.
Part B. Color of Complex.
In order
to observe the color of the complex Cu(CO)Cl(H2O)2,
repeat the reaction above using 30-mL 0.4 M CuCl(aq) solution (prepared
by dilution the stock solution with water in a ratio of 1:3). Under
these conditions, the complex can be observed to have a blue-green color.
from left:
(a) syringe containing CO(g);
(b) immediately after CuCl(aq) is drawn into syringe;
(c) after shaking -- all of the CO reacts leaving air
(d) dilution shows the color of Cu(CO)Cl(H2O)2
|
Experiment 4. Carbon Monoxide Detectors. Equipment:
|
Figure 4. |
You will
need 5 mL CO for this experiment. It is advisable to know how to
reset the alarm prior to performing this demonstration. Place a digital
CO(g) detector in a 1 gallon (4-L) sealable (air-tight) plastic bag and
zip shut with plenty of air locked inside. Plug the device into the
electrical service by pushing the prongs through the plastic bag.
Poke asmall hole with a pencil and work the latex tube through the hole.
Connect the tube to a syringe of CO(g) and slowly inject 1 - 5 mL of CO(g)
into the bag as shown in Figure 4. Most detectors need about three
minutes to register CO(g) so the display will not change right away.
The level of CO should be 250 ppm for 1-mL CO(g) diluted into 4-L air.
| Experiment 5A. Reduction
of CuO with CO(g)
Equipment:
|
Figure 5. |
Start by constructing the reaction chamber. With the assistance of the wire tamping tool provided, push copper wool (from a grocery store Chore Boy cleaning pad - without soap) into the glass pipet as shown in Figure 5.
You will need a syringe filled with CO and a second syringe filled with air before you proceed. Connect the air-filled syringe to the pipet with a short (3 cm) connecting tube. Heat the test tube just below the copper for a few seconds with a gentle burner flame. The copper will begin to darken. Note how the copper becomes black due to CuO:
2 Cu(s) + O2(g)
2 CuO(s)
Attach the CO(g) syringe as shown in the figure and slowly pass the CO(g) through system. The characteristic shiny metallic orange color of copper will immediately return upon exposure to CO(g):
CuO(s) + CO(g)
2 Cu(s) + CO2(g)
This oxidation/reduction process
can be repeated over and over. The gas mixture collected contains
CO2(g) which can be qualitatively characterized with
lime water.
Initially: Pure Cu in test tube oxidizes to black CuO in the presence of air. |
Still at elevated temperatures, carbon monoxide is passed through the CuO-coated copper wool instantly reforming shiny copper metal. |
| Experiment 5B. Quantitative
Reduction of CuO with CO(g)
Equipment:
|
Figure 5. |
Assemble the apparatus shown in Figure 5. The 120 x 15 mm test tube fitted with a suitable (#1) two-hole stopper. The glass tube connected to the CO-syringe goes to within a few mm of the bottom of the test tube. Wrap 2-g copper turnings or copper wool tightly around the long glass CO delivery tube. (We use pieces of copper scouring pads sold in grocery stores.) Begin to insert the wrapped copper turnings into the test tube while maintaining the position of the glass tube through the copper. A wire or glass rod is useful if pushing the copper into the position shown in the figure. Seat the rubber stopper very firmly into position to make sure it will seat properly.
Remove the stopper just far enough to add about 5-g powdered CuO(s) to the test tube. The intensely black powder will gather in the copper turnings. Very little of it should make it to the bottom of the test tube where it could potentially clog the glass CO delivery tube. Reposition the stopper firmly into the test tube as before. Generate two syringes of CO(g). Pass the CO through the system at a rate of about 60-mL/min. Discard the first 25-mL of gas collected because it is mostly air. After the first CO(g) syringe is spent, switch to the second. Continue to collect gas until 60-mL has been collected. This gas is almost entirely CO2. Remove the heat.
The CO2-content of the syringe can be quantified by reaction with NaOH. Draw 10-mL of 3 M NaOH(aq), or 5-mL 6 M NaOH into filled gas-collection syringe. Immediately fit the LuerLOK with a syringe cap. Shake the syringe. The plunger will move inward as the CO2(g) reacts with the aqueous NaOH(aq) forming NaHCO3 and/or Na2CO3. The reaction is:
2 NaOH(aq) + CO2(g)
Na2CO3(aq) + H2O(l)
The amount of gas that remains
represents non-CO2 gases, including air and unreacted
CO. We have achieved >90% conversion to CO2.
Experiment 6. Carbon Monoxide
Poisoning.
Equipment:
| Obtain an absorbent pad from a package of fresh beef, pork or poultry. It is necessary that the pad be soaked with red meat juices. Lay the pad flat in a plastic bag and freeze for easier handling. While frozen, cut the pad into strips that will fit into test tubes. Keep the strips frozen. Fill a series of stoppered test tubes with various gases such as N2, O2, air, and CO. Place one frozen strip in each test tube. Place the test tubes in a rack and store them at room temperature. Observe the test tubes over the next hour and over night. The sample in the CO atmosphere will become very bright red. The others will become gray. Discard all samples without handling. |
Juice absorbent pads from fresh beef after two hours exposure to oxygen (left), air (middle), and carbon monoxide (right) |
Experiment 7. Reduction
of Palladium and Silver Ions with Carbon Monoxide
Equipment:
Pd+2(aq) + CO(g)
+ H2O(l)
Pd(s) + CO2(aq) + 2 H+(aq)
This reaction is used by medical examiners to test for the presence of CO in samples of blood from individuals suspected of CO-poisoning. The appearance of a metallic luster of palladium confirms the presence of CO.
Solutions of 0.1 M AgNO3 are not reduced by CO(g) unless the diamminesilver(I) complex [Ag(NH3)2]NO3 is first formed. Dissolve 1 g AgNO3(s) in 50-mL distilled water and slowly add concentrated ammonium hydroxide solution. A brown precipitate will initially form and then disappear as more (2 - 3 mL) ammonium hydroxide is added. The clear, colorless solution of Ag(NH3)2+ complex will react with CO(g) as described for Pd+2(aq). The reaction is:
2 Ag(NH3)2+(aq)
+ CO(g) + H2O(l)
2 Ag(s) + CO2(aq) + 2 NH4+(aq)
This curious effect was made
by the reduction of Pd+2 as described above.
Subtle vibrations on the
countertop caused the crystals to migrate
into the center of the plastic
cup. PhotoShop was used to
duplicate the image, creating
a "pair of eyes"!
Experiment 8. Reaction
Between Carbon Monoxide and KMnO4
Equipment:
Experiment 9. Catalytic
Converters and Your Car
Equipment:
2 CO(g) + O2(g)
2 CO2(g)
This experiment requires the Gas Reaction Catalyst Tube which is sold by Educational Innovations has specifically designed a for these microscale gas chemistry experiments. The catalyst is housed in a glass tube as shown in Figure 12. 6
Figure 12.6 Gas Reaction Catalyst Tube, shown attached to two syringes.
The assembled apparatus is shown in Figure 12.6. The syringe on the left contains the reagent gas mixture ready to be passed though the catalyst. A 2-cm length of latex tubing connects the syringe to the tubing. To the right of the catalyst tube is the receiver syringe, also connected by latex tubing. The plunger of the receiver syringe must be able to move freely in the syringe barrel. This is assured by lubricating the black rubber plunger diaphragm. Two ring stands and clamps, not shown, hold the two syringes in the appropriate position above the burner's flame. The clamps should not hold the syringes too tightly, and should allow for free rotation of the syringes and catalyst tube for even heating.
Fill
the reagent syringe with 40 mL air (0.34 mmol O2)
and 20 mL carbon monoxide (0.82 mmol.) Cap the syringe and allow
the gases to mix for several minutes. Connect the reagent syringe
to the catalyst tube and assemble the apparatus as shown in the figure.
Pass about 10 mL of gas mixture through the catalyst tube to (a) check
for leaks, (b) determine that the plunger in the receiver flask moves freely;
and (c) displace air (or previous gas mixtures) from the catalyst tube.
(Option: Remove the receiver syringe from the catalyst tube, discharge
the 10-mL air from the receiver syringe and reconnect to the catalyst tube.)
Heat the catalyst tube evenly on all sides for a total of about 30 seconds.
(CAUTION:
Heat from a Bunsen burner flame is capable of softening the glass portion
of the catalyst tube. When the glass is soft, it is susceptible to
deformations and even "blow holes" if the pressure inside the system is
increased by moving the plunger of the syringe. To prevent overheating
the glass, use only a cool Bunsen burner flame. Minimize the amount
of air used so that the flame has a soft, ill-defined blue inner cone.
Position the catalyst tube at least 1 cm above the tip of the inner cone.
Watch for traces of red, orange or yellow in the flame above the catalyst
tube. These colors indicate that the glass is softening. If
this should happen, remove the flame and adjust the flame.)
Slowly pass about half
of the CO/air reagent gas mixture through the catalyst tube over the course
of about 30 seconds. Be alert for problems — the volume of gases
collected in the receiver syringe should almost equal the volume decrease
in the reagent syringe. After half of the gas mixture has been passed
through the catalyst tube, remove the heat. Remove both syringes
and cap them with latex syringe caps. Label the syringes with a marker
pen.
Qualitative test for the presence of CO2(g) is possible by the Limewater test for CO2: Place 10 mL limewater in a 15 x 180 mm test tube. Equip the syringe with a 15 cm length of latex tubing. Discharge 10 - 20 mL of the gas above the limewater solution. Remove the syringe and tubing. Stopper the solution and shake to mix gaseous layer with limewater solution. A white suspension of calcium carbonate confirms the presence of carbon dioxide. CO2:
CO2(g)
+ Ca(OH)2(aq)
CaCO3(s) + H2O(l)
Other catalytic reactions
take place in your car's catalytic converter as well. These reactions
will be discussed in a later chapter.
 |
|
Experiment 10. Demonstrating
the Water-Gas Shift Reaction.
Equipment:
'Water-gas' is the name given to a mixture of H2 and
CO produced by passing steam over red-hot coke:
C(g) + H2O(g)
CO(g) + H2(g)
The CO/H2 mixture can be burned directly as a fuel or reacted further at a lower temperature to convert the CO(g) to more desired products by means of the so-called the 'water-gas shift' reaction:
CO(g) + H2O(g)
CO2(g) + H2(g) DH
= -41.0 kJ DS
= -42.3 J/K
The water-gas shift reaction, which we will demonstrate in this experiment, is catalyzed by iron or Fe3O4 at elevated temperatures.
The apparatus used for this reaction is shown in Figure 6. The 15 x 180 mm test tube is fitted with a 2-hole stopper equipped with a long glass tube that extends to 2-mm from the bottom of the test tube and a shorter glass tube. The latter is connected to the gas collection syringe by a short piece of latex tubing. An additional gas collection syringe is necessary. Lubricate the plungers of the gas collection syringes; they must move easily. Steel wool comes coated with a protective film to reduce oxidation. Unfold a 4 - 5 g piece of fine (#00) steel wool. Hold the steel wool with crucible tongs and ignite it from the bottom with a small burner (butane lighter) flame. The organic film will burn with the production of considerable smoke, leaving behind Fe3O4. Remove the stopper from the test tube just far enough to wrap a 2.0-g piece of the burned steel wool around the long glass tube and work it down into the test tube. The steel wool should be densely packed. Re-seat the stopper. The glass tube should run through the steel wool as shown in the figure. With a pipet, add 1-mL H2O(l) to the test tube via the long glass tube. The glass tube should be under the surface of the water.
Generate two syringefuls of CO(g). Push 30-mL CO through the system via the long glass tube. This purges the system of air. Switch syringes so that a full syringe of CO(g) is available for the reaction. Heat the test tube to near its softening temperature (ca. 400 oC) directly below the steel wool (and not the water). Radiant heat will cause the water to start to boil. When the water begins to boil, slowly deliver the CO(g) from the syringe. As it bubbles through the water, it sweeps H2O(g) with it through the steel wool, where the reaction is catalyzed. In order to prevent steam burns, do not switch syringes while the system is hot.
The gas collection syringe contains CO2(g) and H2(g) along with unreacted CO(g) and H2O(g, l). The contents of the syringes can be qualitatively tested for CO2(g) using limewater.
As
a 'control', repeat the experiment without heating the catalyst.
No CaCO3(s) will appear in the limewater test.
|
|
Photograph of assembly shown in Figure 8. |
At the
end of the experiments, wipe excess lubricant off of rubber diaphragm.
Clean all syringe parts (including the diaphragm), caps and tubing with
soap and water. Use plenty of soap to remove oil from the rubber
seal. This extends the life of the plunger. It may be necessary
to use a 3-cm diameter brush to clean the inside of the barrel. Rinse
all parts with distilled water. Be careful with the small parts because
they can easily be lost down the drain. Important: Store plunger out of
barrel.
| This article first appeared
in Chem13 News in March, 1999. The authors of the original
Chem13 article are:
From the Department of Chemistry, Creighton University, Omaha, Nebraska 68178 USA: Also from Creighton University:
Rimantas Vaitkus, Department of Chemistry, Vilnius Pedagogical University, 2034 Vilnius, Lithuania *Author to whom correspondence should be addressed. E-Mail: xenon@creighton.edu |
Some of the CO-researchers: from left: Maneesh Bansal, Andrew Mattson, Anand Rajani and Rebecca Catahan.
|
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