The three gases used in this experiment are the
three easy gases, carbon dioxide, hydrogen, and oxygen. A fourth
gas,
nitrogen, which is also easy to generate can be added to make the
experiment more
challenging. This laboratory experiment tests students’
abilities
to
identify the three (or four) gases based on their
differences.
Students
must design an experiment to make the correct identification.
By way of review, the following list summarizes
3 –
4 experiments that were performed by the students on each gas.
Experiments performed on carbon
dioxide:
Experiment 1.
Traditional limewater test for carbon dioxide.
Experiment 2. Acidity of
carbon dioxide
Experiment 3. Carbon
dioxide extinguishes fires
Experiment 4. Carbon
dioxide and aqueous sodium hydroxide react.
Experiments performed on hydrogen:
Experiment 1.
Traditional test for hydrogen.
Experiment 2. Hydrogen
bubbles are flammable
Experiment 3. Reduction of
CuO(s) with hydrogen
Experiments performed on oxygen:
Experiment 1.
Traditional test for oxygen
Experiment 2. Oxygen
supports combustion
Experiment 3. Dynamite soap
Students should design a series of experiments
to
correctly identify samples of each of these gases from the list
given
above.
INFORMATION
FOR THE TEACHER
Suitability
This laboratory activity is suited for high
school
chemistry students.
Background skills required
Students should be able to:
perform the
student experiments for carbon dioxide, hyrogen and oxygen
design an experimental
procedure
Time required
Students should be able to perform this
experiment
in a single 45 minute laboratory period.
Equipment
Microscale Gas
Kit
Piezoelectric lighter or
match
Chemicals
To make a gas
bag
full of CO2: Use 3 g NaHCO3
and 50 mL of vinegar
To make a gas bag full of H2:
Use 1 g magnesium and 50 mL 1.2 M HCl(aq)
To make a gas bag full of
O2: Use 0.5 potassium iodide and
60 mL 3%
H2O2(aq)
limewater
universal indicator
solution
concentrate ammonium
hydroxide solution (only the NH3
fumes
are needed)
magnesium ribbon
phenolphthalein solution
3% dish soap solution
Before students arrive
Prepare gas bags
filled
with
carbon dioxide, hydrogen, and oxygen.
Instructions
Each group of students will receive 3 syringes
marked “A” “B” & “C”. Each of the three syringes will
contain
a gas:
CO2(g), H2(g),
and O2(g). The students
themselves
will not know what gas is in what syringe by simply looking at the
syringes.
Vary the order from group to group. The students will be
asked to
perform test on each of the syringes using the information and
data
collected from prior Microscale Gas Experiments done for CO2(g),
H2(g), and O2(g).
Student instructions
For classroom use by teachers, one copy per
student
in the class may be made free of charge and without further
permission.
Student instructions and questions only (without teaching tips,
suitability information, etc.) can be downloaded free of charge as
a
Microsoft Word
document from the website. Would you like to download this
file
now?
Yes!
MYSTERY
GAS. INSTRUCTIONS
FOR
STUDENTS
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 dioxide, hydrogen and oxygen are all
relatively non-toxic. The first two are asphyxiants if
inhaled in
quantities
much larger than we will encounter today. Even pure oxygen
can be
toxic if inhaled in large quantities. Do not intentionally
inhale
any
samples of gas in these experiments.
Your assignment
You and your lab partner will be given three
syringes filled with three different gases, carbon dioxide,
hydrogen
and oxygen.
Your assignment is to correctly identify the contents of each
syringe
using the experimental procedures previously conducted.
Design an experiment
Design a method to identify each gas from the
three
possibilities, carbon dioxide, hydrogen and oxygen. You may
use
any
of the following experiments that you have already performed.
Experiments performed on carbon dioxide:
Experiment 1.
Traditional limewater test for carbon dioxide.
Experiment 2. Acidity of
carbon dioxide
Experiment 3. Carbon
dioxide extinguishes fires
Experiment 4. Carbon
dioxide and aqueous sodium hydroxide react.
Experiments performed on hydrogen:
Experiment 1.
Traditional test for hydrogen.
Experiment 2. Hydrogen
bubbles are flammable
Experiment 3. Reduction of
CuO(s) with hydrogen
Experiments performed on oxygen:
Experiment 1.
Traditional test for oxygen
Experiment 2. Oxygen
supports combustion
Experiment 3. Dynamite Soap
Conduct the experiment
Locate the necessary chemicals and equipment
needed
to perform the proposed experiments. Record all results in
your
laboratory notebook.
Clean-up and storage
At the end of the experiments, clean all
syringe
parts (including the plunger seal), caps and tubing with soap and
water.
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.
Questions
1. What
experiments allowed you to conclusively identify each gas?
2. What would happen if
you performed the experiment given for one particular gas on a
different gas?
For example, what would happen if you performed the limewater
test on
oxygen?
3. Identify a gas that
causes hot copper to darken and does not form acidic solutions
with
water.
4. Why is “Dynamite Soap”
not as useful as other experiments for the identification of
gases?
5. If you had to pick only
one experiment to try to identify each gas, which one would you
pick
for each
gas?
This
page updated on 26 Oct 2016
Download
pdf of Mystery Gas from our book Microscale
Gas Chemistry