Notes for Mini-Hindenburgs (#44)
Steve Sogo, Laguna Beach High School ssogo@lbusd.org
Overview: In this lab, students investigate the reaction rates of zinc and aluminum with
hydrochloric acid. A central mystery is why the reaction of aluminum pellets with hydrochloric
acid starts so slowly. After performing an initial scripted reaction, students design experiments
to test variables that may increase aluminum’s reaction rate. This lab is best done after students
have some knowledge of single-replacement reactions (electron-transfer reactions) involving the
activity series.
Why do this lab?
 The reactions, including the capture of gas in balloons, are visually appealing
 Exploding the hydrogen-filled balloons at the end of the class is fun!
 Students are empowered to design an experiment based on scientific principles. Ideally,
students apply a molecular/atomic perspective to intelligently design an experiment to
enhance the reaction rate of aluminum.
 In addition to investigating reaction rates, the lab also includes stoichiometric
calculations.
Materials:
For each lab station:
 2 x 125 mL Erlenmeyer flasks
 1 x 200 to 300 mL Florence flask (used for the student-designed experiment)
 9” helium-quality balloons required (3 per table) Can be distributed via the buffet table.
Preselected pieces of zinc and aluminum provided on a central “buffet table”. Jars should be
clearly labeled. PLACE PAPERS ON BUFFET TABLE TO REMIND STUDENTS how many
pieces to take!
 Mossy Zinc = students use a single lump of 1.5 to 3.5 grams
 Aluminum pellets = students instructed to use two pellets (total mass = 0.6 to 1.2 grams)
Instructor should be prepared to provide upon request:
1. 10 M HCl (undiluted pool acid)—acid concentration is a testable variable PHOTO?
2. Granulated aluminum metal—provides a greater surface-to-mass ratio
3. Aluminum foil—provides a much greater surface-to-mass ratio
4. Copper chloride for “skinning” aluminum pellets—CuCl2 (aq) is able to dissolve the
outer “skin” of aluminum oxide present on the pellets
5. Microwave to heat HCl (or hot water bath?)—temperature is a testable variable
6. Sandpaper/file for physically abrading aluminum pellets to remove the oxide layer
Video Support:
An Instructional Video is available at http://youtu.be/1X5Fn4VrrNg. This video demonstrates
how to attach balloons to flasks, discusses acid molarity (shows dilution process), and
demonstrates the explosion of hydrogen-filled ballons.
An additional video is available at http://youtu.be/xOHBJc6CIqg showing the results of
experiments done to remove the aluminum oxide layer on the pellets.
Comments:
1. This lab is designed for a 90-minute period.
2. The key to this lab’s success is meaningful discussion between instructor and students as they
are considering the design of their self-directed experiment. Students will often have a good idea
(e.g. increase the surface area of the metal), but will be unable to see how to test the idea
scientifically. For example, many students will want to add more pellets of aluminum instead of
changing to aluminum foil or granulated aluminum. The instructor should listen to student ideas
and help guide them to develop a well-controlled experiment.
3. This lab words best when different groups investigate different variables. The instructor
should steer each group to develop an experiment that does not “copy” the work another group is
doing. In a class with 8 or 9 lab groups, some duplication is likely to occur, but to have many
groups doing the same experiment is counterproductive. The lab instructions encourage students
to circulate at the end of the period to discover what other groups have done and extend their
learning through this discussion process.
4. Good ventilation is required at the end of the period when the balloons are exploded. A fume
hood or exhaust fan may be helpful.
5. Occasionally, the rubber of a balloon will ignite when placed in a Bunsen burner flame.
Dunking in water will extinguish this flame.
6. Students must wear glasses during the explosion phase!
7. A large wash acid jar must appear on buffet table to collect the liquid remains from student
flasks. This wash acid is useful in descaling glassware and can be stored for use throughout the
school year.
Assignment #44: Mini-Hindenburgs
Hydrogen go Boom!
Overview: In this lab, you will react samples of aluminum and zinc with hydrochloric acid to generate
hydrogen gas. You will use a balloon to capture the hydrogen that is generated. At the end of class, we
will ignite these balloons to create some nice explosions.
There central concept you will be investigating in this lab is: What factors determine the SPEED of an
electron transfer reaction (the reaction rate).
Step 0: Put on Safety Gear! You also need a periodic table and calculator.
Step 1: Obtain metals.
Obtain two pieces of aluminum metal and one piece of zinc metal from the designated supply jars on
the buffet table. Weigh each sample of metal.
Total Mass of Al = ___________
Mass of Zn = ____________
Step 2: Balanced equations for electron transfer reactions.
In the space below, write a balanced equation for the reaction of ZINC METAL with HYDROCHLORIC
ACID (include phase notations!) and a balanced equation for the reaction of ALUMINUM METAL with
HYDROCHLORIC ACID. In each of these reactions, identify the electron donor, the electron acceptor, and
the spectator ions.
Eqn #1:
Eqn #2:
Step 3: Thinking about the chemistry that occurs.
The concepts listed below all affect the rate at which the reaction depicted above will occur. For each
concept, jot down an idea for how/why this factor will affect the rate of the electron transfer reaction:
i. The speed at which ions swim through the aqueous medium
ii. The extent of the metal’s surface area exposed to the acid
iii. The metal’s position on the activity series
iv. The concentration of hydrogen ions within the aqueous solution
After discussing the concepts given above, make a PREDICTION (a sentence) for which metal (Zn or Al)
will react FASTER in this experiment. Defend your prediction.
Assignment #44: Mini-Hindenburgs (continued)
Step 4: Experimental procedures.
0. You must be wearing proper safety glasses and shoes for all experimental work.
1. Pour 20 mL of 6-molar HCl in each Erlenmeyer reaction flask.
2. Drop your metals into each flask simultaneously (or as close to simultaneous as possible).
Place a balloon atop each flask to capture the gas produced. Note: be prepared so that you
don’t lose any initial burst of gas!
3. As your reactions run, answer the questions on the next page. Note: the question page
will be turned in for credit.
4. When you get to question C on the question page, discuss ideas and devise an experiment
with the help of your instructor. You will use a Florence flask (the round flask) to run the
reaction you have designed.
5. 10 minutes before the end of the class period, VISUALLY ESTIMATE THE VOLUME of
hydrogen collected in each reaction by comparing the size of the balloons to objects of
known volume, such as a 400 mL beaker, a 1-liter cube, etc. Write these estimates in the
proper spaces on question D.
6. Talk to neighboring groups to learn about their experimental methods and results.
7. TERMINATE your reactions by REMOVING THE BALLOONS AND TYING THEM SHUT (don’t
lose your hydrogen gas when you do this!!!). Do this even if the reactions are not completed.
8. Dump your leftover acid solutions into your instructor’s large WASH ACID bottle (on the
buffet table). Shake leftover bits of metal into the trash (not in the sink!!!).
9. At the end of the hour, your hydrogen-filled balloons will be ignited in a designated spot
(your INSTRUCTOR MUST SUPERVISE the explosions). To ignite the balloons, you will need
to hold your balloon with TONGS and bring the balloon into the flame of a Bunsen burner.
EVERYONE MUST WEAR SAFETY GLASSES DURING THESE EXPLOSIONS!
10. Help your instructor CLEAN UP the mess made from the exploding balloons.
Write-up instructions:
For this lab, you will do a “hybrid” write-up. EVERYONE WILL TURN IN THE QUESTION SHEET.
This question page will give you 7.5 points (if it is well done). If you want to earn more than 7.5
points for the lab, you must also turn in a paragraph-based write-up (typed or hand-written) that
covers the following topics:
Start with an introduction that summarizes what happens in this E.T reaction (i.e. who
swims, who sits immobile, who is strong, who is weak, where the electrons go).
Follow with a theoretical discussion that discusses your IDEAS about the factors that
influence the rate of the reaction. Show your thoughtfulness by using well-crafted sentences
(possibly with supporting diagrams). You’re trying to explain WHY the reaction rate should
depend on various factors. Try to relate your discussion to the atomic scale picture shown
on the previous page.
The next section (analysis of experimental work) should discuss the RESULTS of your
experiments in a manner that relates to the theoretical IDEAS discussed earlier. Discuss
your self-designed experiment in detail—try to sound like a professional scientist (thoughtful
design, keen observations, intelligent interpretation of data). You are encouraged to include
the experimental results of other groups in your class when you write this section.
Assignment #44: Mini-Hindenburgs--Lab Questions:
A. An electron transfer reaction can be thought of as a struggle (or competition) for electrons. In these
reactions, are the METALS (zinc and aluminum) acting as ATTACKERS or DEFENDERS? Explain.
B. All acids contain H+ ions. Would another acid such as hydrobromic acid (HBr) or sulfuric acid (H2SO4) be
a reasonable acid to substitute for the HCl in this lab? That is, would the electron transfer still occur if you
used HBr instead of HCl? Hint: think about the role of “spectator ions”.
C. You may have been surprised that the aluminum reaction starts out as a real dud. When the aluminum first
hits the acid, there is little to no reaction visible. However, as time goes by, the aluminum’s rate of reaction
becomes faster and faster. Discuss ideas for WHY the aluminum’s reaction is slow at first and then INVENT AN
EXPERIMENT for how to increase the aluminum’s initial reaction rate. When you think you have a good idea on
how to speed up the aluminum’s reaction, CONSULT WITH YOUR INSTRUCTOR so that you can run your
experiment with proper scientific controls.
Describe your experiment in the space below, INCLUDING YOUR UNDERLYING HYPOTHESIS (the WHY).
D. Using calculations similar to those shown below, calculate the VOLUME of hydrogen gas that should be
produced in each of your reactions (given the weights of metals you used in these expts). Then compare these
CALCULATED volumes of gas to the VISUALLY ESTIMATED SIZES of your balloons. If your calculation doesn’t
match your visual estimation, you may have made an error in calculation.
Note: the density of H2 (g) = .089 grams per liter
Visual estimates for balloon volumes
Sample calculation: Imagine you reacted 1.22 grams of Mg metal
with HCl:
Zinc rxn
Original Al rxn
Modified Al rxn