In this lab, students create a stoichiometric mixture of hydrogen and oxygen gases to launch a soda bottle rocket.
This lab will help prepare your students to meet the performance expectations in the following standards:
- HS-PS1-7: Use mathematical representation to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.
- HS-PS3-3: Design, build, and refine a device that works within given constraints to convert one form of energy into another form of energy.
- Scientific and Engineering Practices:
- Using Mathematics and Computational Thinking
- Developing and Using Models
- Analyzing and Interpreting Data
By the end of this lab, students will
- Understand the importance of limiting reactants.
- Witness a combustion reaction.
- Construct a rocket that demonstrates understanding of many chemical concepts.
This lab supports students’ understanding of
- Limiting reactant
- Activation energy
- Gas laws
Teacher Preparation: 2 hours
Lesson: 3 hours
For each group:
- Soda bottle (2 L or 1 gal)
- 1-L graduated cylinder
- Water trough
- 125-mL flask with #5 stopper
- 250-mL flask with #6 Stopper
- Tygon/rubber tubing (about 18” length) with dropper tip
- 10% hydrogen peroxide (Dilute one part Baquacil Shock and Oxidizer with two parts water. Ex 250 mL of Baquacil + 500 mL of distilled H2O)
- Weighing paper
- Potassium iodide
- Calcium (calcium from Flinn works best)
- Aluminum foil
- Index cards
- It’s recommended to view the PowerPoint provided by the creator of this activity for proper set up, execution, and further safety tips.
- Always wear safety goggles when working in a chemistry lab.
- Even when the rocket is prepared, still wear safety goggles. When carrying the rocket from the lab to the field, be cautious.
- When launching, keep all students at a safe distance (approximately 50 feet) except for those who are setting up their rocket.
Please review the video below created by Steve Sogo, the instructor, to learn about safe execution tips of this activity with your class.
- An alternative outcome is achieved if students use juice, water, or milk bottles instead of soda bottles. Soda bottles can withstand high internal pressures, while juice, water, and milk bottles will explode when internal pressure rises. If a H2 + O2-filled juice, water, or milk bottle is ignited, a very loud explosion will be created, shredding the bottle to bits.
- Introductory Video available at Youtube Channel ACR92651: Rockets!!!
- This lab activity was originally designed to be run as a one-week project incorporating many different chemical concepts. The lab can be shortened (possibly to as little as two days) by cutting out the activation energy and catalysis concepts.
- Students can construct aluminum foil electronic igniters that they use to launch the rockets safely by plugging in a 50-foot extension cord. Upon ignition, each soda bottle will briefly display a flash of fire, which will propel the bottle into the air. Video: Rocket Igniter Construction
- If students have a 2-liter bottle, they should have calculated a volume of about 20 mL of H2O2. If they have a 1-gallon bottle, they should have calculated about 35 mL of H2O2.
- Remind students they don’t need to mass exactly 0.7 g of KI. The quantity of catalyst does not affect the quantity of oxygen created, only the rate at which the gas is created.
- If students have a 2-liter bottle, they should find they need close to 2 g of calcium. If they have 1-gallon bottle, the calculated mass should be around 4 g of calcium.
- An additional file, Student Worksheet—Activation Energy,can be used as a formative or summative assessment piece.
- Teacher introduce project expectations
- Lab groups assigned
- Each group begins stoichiometric calculations using the bottle they have brought
- Goal is to complete the activity through step 4c (if not met during class, students may complete as homework)
- Teacher discusses activation energy and catalysis—the energy diagram for combustion of magnesium metal is a good illustrative example.
- Students use Interactive Physics to model how a catalyst works
- Students continue completing the activity through step 5d
- Teacher shows students how to construct aluminum-foil igniters (instructional video available at: Rocket Igniter Construction)
- Aluminum foil, index cards, scissors, and rulers supplied for student use
- Students build at least two igniters and test at least one igniter using a 12-V transformer. Goal is to produce an instant spark upon plugging in the transformer.
- Students produce step-by-step instructions for launch day. Students must translate the information contained in the lab packet into a protocol: What must be done first? (fill bottle and trough with water!) What next? The teacher could also provide pages 5 and 6 from Student Activity Sheet, which contains a suggested protocol.
Days 4 & 5
- At my school, Thursday and Friday are 100-minute block periods, allowing for both generation of gases and launching of nine rockets per class without rushing. If only short periods are available, I recommend filling the bottles with O2 on day 4 and leave the bottles partially filled with water so as not to create an explosive mixture within the bottles. Then students will need to efficiently complete the filling of each bottle with H2 and proceed to launch the rockets on day 5.
- Teacher shows the instructional video to discuss how to generate O2 "perfectly" by packaging the KI catalyst. KI catalyzes the decomposition of H2O2 to generate oxygen gas.
- Students set up water displacement troughs and generate O2 gas, collecting the O2 in the soda bottles using displacement of water (the O2 should fill 1/3 the volume of each bottle).
- Students then generate H2 gas using the reaction of calcium with water (or a suitably active metal with acid). H2 is collected in the soda bottle until all the water in the bottle has been displaced.
- The bottles are ready for launch. Instructional video for launch procedures: Rocket Launching.
- Launch Tips
- I recommend using a pair of extension cords, one at least 50-feet in length. Rocket ignition is initiated by plugging the two extension cords together, transmitting power to the 12-V transformer. Ignition should be instantaneous. If ignition does not occur, the cords may be unplugged to allow troubleshooting. The most common cause of failure is a bad igniter or bad electrical connections.
- Test that the transformer is "live" by using a voltmeter (or tapping the alligator clips together to observe sparking) prior to trying to launch any rockets.
- Keep all students at a safe distance (approximately 50-feet) except for those who are setting up their rocket.
- When going outdoors to launch, bring a big cardboard box to act as a windbreak, scissors, masking tape, transformer, sharp pencil (to separate tip of aluminum foil igniter), paper towels, trash bags, launch pads with various rings.
- A ring stand with several rings of varying diameters works well as a launch pad.
- One member of each student team should be designated to be "on the cord". This student should clearly demonstrate that the extension cords are NOT plugged in while students (and teacher) are setting up the launch pad.
- Plug your ears if igniting a gallon jug! The explosion can be deafening (and may set off car alarms nearby).
For the Student
You will make a rocket using plastic bottles with volumes between 1 L and 4 L. You will fill the bottles with a mixture of hydrogen gas and oxygen gas in an appropriate ratio. When ignited, the reaction will produce water gas at a very high temperature. The hot molecules will generate a propulsive force (or the bottle will simply blow up).
- The first thing to determine is the appropriate ratio of hydrogen and oxygen to use in your rocket. You need an explosive mixture to launch your rocket. A mixture too rich in H2 will burn quietly like a Bunsen burner instead of igniting explosively. A mixture too rich in O2 will explode, but weakly. A mixture that is just right will produce maximum power for your rocket. The unbalanced equation for the propulsion reaction is as follows:
H2(g) + O2(g) → H2O(g)
If you balance the equation shown above, you will know the correct mole ratio of H2 to O2 needed to achieve the maximum propulsive force.
- Use a 1-L graduated cylinder to accurately measure the total volume of your bottle. Using the mole ratio of H2 to O2 that you discovered from your balanced equation, you can figure out how much H2 and how much O2 you will need to fill the plastic bottle. In the space below, sketch a picture of your bottle (label total volume) and draw a line showing what fraction of the bottle you will fill with H2 and what fraction you will fill with O2. Convert these fractions into actual volumes of H2 and O2 (in liters). Discuss how the mole ratio compares to the volume ratio that you sketch in your picture.
- Use the ideal gas law and your picture above to calculate how many moles of H2 you will need, and how many moles of O2 you will need in your bottle. Also give a one-sentence explanation for why 22.4 L/mole is not a valid measurement to use for this experiment.
You just determined how much H2 and O2 you need for your rocket, but you will have to generate these gases by running chemical reactions.
This part discusses production of O2 gas.
- O2 can be generated from the decomposition of H2O2. The unbalanced equation is:
H2O2(l) → H2O(l) + O2(g) ΔH = -190 kJ/mol
The reactant in this reaction, hydrogen peroxide, is thermodynamically unstable and can rearrange its atoms to form water and oxygen gas. This reaction is extremely slow at room temperature unless a catalyst is added. You will use potassium iodide (KI) as a catalyst to speed up this reaction. When running the actual reaction, a small scoop of the catalyst (about 0.7 grams ) will be “packaged” in weighing paper and then added to the H2O2. You will place the stopper on the reaction flask and then shake it to allow KI to come out of its package. This method should enable you to collect ~100% of the gas created in this reaction.
- Balance the equation shown above and use stoichiometry to calculate the mass of H2O2 needed to generate enough O2 for your rocket. (Remember, you calculated the O2 quantity in step #3.)
- The H2O2 that you will use to generate O2 is a liquid, which is a solution of H2O2 and H2O. The solution contains 10% H2O2 by mass, the other 90% is H2O. Use your value from (a) to calculate how many grams of the solution you will need. You can draw a picture of what the 10% solution of H2O2 will look like to help with this calculation.
- Assume the 10% H2O2 solution has a density of 1.0 g/mL. Convert the grams you calculated in (b) into milliliters of solution.
- Refer to the sketch that represents the energy diagram of the uncatalyzed decomposition of H2O2.
i. In the sketch, label the following: H2O2, H2O + O2, activation energy (Ea), and DH.
ii. Below, sketch an energy diagram for the catalyzed decomposition of H2O2. Then, to the right, explain how the catalyst helps the reaction proceed at room temperature.
This part discusses the production of H2.
- Hydrogen can be generated in many ways. You will use the method shown below:
Ca(s) + H 2O(l) → H2(g) + Ca(OH)2(s) ΔH = _________
- Balance the equation shown above.
- Calculate DH for the reaction (in kJ/mole) with the following information: the reaction is exothermic and produces 10.4 kJ for each gram of calcium that reacts. Write the calculated value in the space provided above.
- Use stoichiometric calculations to determine the mass of Ca and volume of H2O needed to produce enough H2 for your rocket. Remember, do you know how much H2 you need?
- The amount of H2O you have calculated is the amount that will actually react with the Ca that you will weigh out. This is not a smart way to run this reaction. Circle two of the choices below that express reasons why it is a good idea to add excess H2O when you carry out this reaction. When you run the reaction, you will want to use a large excess (as large as your reaction flask permits). To the right, sketch what your flask should look like if you use a large excess of H2O.
- i. extra water will create extra hydrogen
- ii. extra water will create more heat in the reaction flask
- iii. extra water will keep the reaction flask cool
- iv. extra water will reduce the amount of air that goes into the rocket
- e. Calcium is a very reactive metal. Even while inside its jar, the outer surface of calcium is oxidized to some extent (forming CaO). This reduces the amount of actual calcium in the lumps that you will use. How can you correct for this problem?