Lab 4B – Putting Bubbles to the Test
Safety Note Wear safety goggles and aprons.
In Lab 4A you attempted to discover an unknown gas that “turns
limewater cloudy, turns Phenol red yellow, and extinguishes a lit match”. There is
one common gas that fits this operational definition. It is called carbon dioxide.
With this information a simple word statement can be written describing what
you did to get carbon dioxide. Shell + HCl → Carbon Dioxide. The “+” in the
word statement means you mixed the shell and HCl. The arrow “→” means
produces (or yields). This word statement is read, “ Shell and HCl, when mixed,
produces carbon dioxide”.
Keep in mind that you are gathering evidence to develop the particle
model and make it more useful. According to the model, shell, HCl, and carbon
dioxide are composed of tiny invisible particles. The carbon dioxide particles were
the result of mixing shells and HCl particles.
Suppose carbon dioxide could be produced by mixing HCl with other
materials. Would this mean that the particles in the other material were like the
particles in shell? And does HCl react with substances other than shell? In today’s
lab you will be able to answer these questions.
Working with your lab partner, you will need to gather the following
equipment from the supply area and bring them to your lab table:
1. 1 prepared test tube rack containing 5 test tubes of various materials
2. 1 small 10ml air piston
3. 1 50ml beaker of HCl from the fume hood
Question 1 In your notebook create and enlarge the following Table for
completion:
Test
Tube
#
Material & Amount
1
3ml ammonia solution
2
2ml lead nitrate solution
3
1 small piece of chalk
4
1 pinch of baking soda
5
1 small piece of zinc
Appearance Before
Adding HCl
Observable
Changes After
Adding HCl
Be sure to make observations using 4 of your senses, do not taste. Waft for
odor, hold test tubes for temperature, look for sight, and listen for hearing.
Activity A Make observations of each of the 5 test tubes and record them in
your Table.
Activity B Fill the small air piston with 2ml of HCl from the 50ml beaker.
Activity C (Keep all test tubes in the rack while adding HCl). Beginning with test
tube #1, hold the air piston approximately ½ inch above the open test tube and
add 2ml of HCl. Carefully place the air piston flat on a paper towel. Do not leave
it in the beaker for it might spill over! After 1 minute, record your observations of
any changes that occurred in the last column of the Table. If no observable
changes occurred, write “none”.
Activity D Repeat activity B & C above for the remaining 4 test tubes and record
your observations in the Table.
Question 2 List those materials that produced a gas when HCl was
added.
Question 3 How did ammonia solution and lead nitrate solution behave
when HCl was added to them?
Question 4 In what way was the behavior of chalk, baking soda and
zinc the same when HCl was added to them?
Several of the test tubes produced a gas. Can the gas be carbon dioxide in
each case? The operational definition tells you how to find out. Remember, “I
know I have carbon dioxide gas if limewater turns cloudy, Phenol red turns
yellow and a lit match is extinguished (goes out).”
You should test each of the combinations from the Table that produced a
gas. Testing the gas with a lit match requires a large sample. Therefore, you will
not use that test. The limewater and Phenol red tests will be enough to show
whether or not carbon dioxide is present. Large samples are not needed for
those two tests. You won’t need to collect jars of gas, either. You can bubble the
gas produced from each mixture through a few milliliters of limewater and then
through Phenol red solution. Therefore, in the next lab, you need to test the gas
produced by HCl and each of chalk, baking soda and zinc to have enough
evidence to make your conclusion whether or not the gas produced is carbon
dioxide.
Clean Up Now that you have finished all lab work, clean and put away your
equipment in the supply area as directed. Specifically,
1. Take the remaining 50ml HCL beaker back to the fume hood. Do not
rinse it out.
2. Take your test tube rack and air piston to the sink. Turn on the water.
3. Rinse out the air piston and return to the supply area.
4. Working with one test tube at a time, add water to the test tube and then
dump the test tube contents into the sink while the water runs.
5. Use the test tube scrubber to quickly and carefully wash each test tube.
6. Place the now cleaned test tube upside down on the rack pegs for drying.
7. Turn off the water and pick out the zinc and chalk pieces from the sink
and place them in the jars by the faucet.
8. Return the test tube rack to the supply area as directed.
9. Wipe down lab tables with damp paper towels and discard in the trash.
10.
Return safety glasses to the cabinet and fold away aprons.
11.
Wash hands with soap and water at any of the four sinks.
STOP here for today.