HYDROGEN-OXYGEN ROCKETS

David A. Reierson
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Initial Publication Date: August 15, 2008

Summary

In this chemistry lab, students investigate how to build and launch a simple rocket that uses hydrogen and oxygen gases that will be mixed to propel the rocket (large bulb plastic pipette). Students will understand the principles of combustion reactions, kinetics, stoichiometry of reactions, activation energy, explosive mixtures, rocketry, and different types of chemical reactions. Students will explore and determine the proportions of hydrogen and oxygen mixture that will achieve the best launch results. Students will compare the balanced chemical reaction of hydrogen and oxygen with their lab results; students should discover that the optimal distance occurs when the mixture of hydrogen and oxygen is two to one hydrogen, oxygen mixture ratio and this can be determined theoretically from the balanced chemical reaction equation. Students will perform the lab, collect data, and discuss, compare, and contrast their lab findings with the balanced chemical reaction equation. Students will present their structured inquiry investigations using a power-point presentation. Other groups along with the teacher will assess each group by using a provided rubric. Group assessments will be the deciding assessment for the final lab score. A follow up activity could investigate how NASA scientists launch real rockets into space and propose a procedure to investigate and collect data on a launching a heavier object at the school football field.


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Learning Goals

This activity is designed so students will be learning in a structured setting and participating in a structured inquiry level through a controlled scientific experiment. During the activity, students should be able to construct a plastic bulb pipette rocket and test the rocket with varying mixtures hydrogen and oxygen by igniting the mixture with a high voltage tesla coil. The ratios will include zero to zero, ambient air, the control for the experiment, one to one, one to two, and two to one, hydrogen oxygen respectively for experimental trial. Students will launch their rockets at a forty five degree angle, a constant during all trials, and measure the distance the rocket travels from the launch platform. This activity directly meets the Minnesota State standards for chemistry content in several areas. Goal two is that students will observe and manipulate variables to better understand the fundamental chemistry concepts: principles of combustion reactions, kinetics, stoichiometry of the reactions, activation energy, explosive mixtures, rocketry, and different types of chemical reactions. This activity is designed for students to: use higher order thinking skills (critical thinking, math use in science, data analysis, synthesis of ideas, and modeling) that are developed by the rocket activity. This activity promotes critical thinking, data analysis, observation techniques, lab techniques, questioning, and other skills and equipment operations). The third goal is that students will review and use "Key" vocabulary words and ideas to better understand the significance of: balancing equations, combustion reactions, kinetics, stoichiometry, activation energy, explosive mixtures, rocketry, and types of chemical reactions. Finally, the most important goal is for students to explore and expand on their newly acquired information by investigating and researching a similar concept. Students will research and investigate how NASA scientists launch Saturn vehicles through the use of liquefied gaseous hydrocarbons and liquid oxygen for the rocket's first stage and liquid hydrogen and liquid oxygen for the second stage of the launch sequence. One follow-up activity might be to launch a 2-liter bottle filled with hydrogen at a remote location and analyze the rate mechanisms related to the hydrogen/oxygen combustion reaction.

Context for Use

This activity could include students in grades 9-12. We are an urban public school. There are 20-35 students in my class on any given day and hour. Students are divided up into small groups of four. Special equipment, including a high voltage tesla coil, wide-stem disposable pipettes, and pure hydrogen gas and pure oxygen gas, would be suggested for this activity. I would suggest not creating your own hydrogen gas and oxygen gas for this activity because I found that many students were not successful mixing pure gases properly. It would require some modification to meet the needs of all learners due to prior experience both in science and math. It requires some lecture, lab procedures, math skills demonstrations, and assembly modeling and demonstrations by the teacher. You should expect about three full days to develop all the concepts, building the rockets, launching the rockets, and fine tuning the hydrogen/oxygen ratio for maximum flight distance. It would be encouraged to discuss the balanced chemical reaction before the lab is conducted and perform a demonstration of various launch angles and procedure for igniting the fuels in the rocket. Students should be able to solve a one variable algebraic problem, understand that electrical current flows in a conductor to ground (high voltage tesla coil to ground), understand that the tesla coil generates a large kilovolt pressure to ignite the gases, and have been introduced and practiced stoichiometry and gas laws. Additionally, students should have some experience with small hand tools required to build the rocket launch mechanism.

Description and Teaching Materials

The lesson will be introduced as a lab during the stoichiometry unit and revisited or as a stand alone lesson during the gas laws unit. The lab works well to introduce gas law concepts in middle school lab, high school lab, and/or a classroom demonstration. To get started, show students during a demonstration how to prepare a mixture of O2 and H2 by displacing the water filled pipette with O2 and H2. This can be accomplished by transferring the gases from two different baggies filled with O2 and H2 via a straw with a non-polar lubricant for sealing purposes. Slowly squeeze the desired amount of gases from the baggy into the pipettes as needed. The procedure for filling and launching rockets is summarized here:
1. Cut the end off of a pipette leaving about 2 cm of stem attached to the bulb.
2. Immerse the pipette in a pan of water and completely fill the "rocket" with water.
3. Slip the water-filled "pipette rocket" into the straw end which is attached to the gas filled baggy. Slowly displace the water with the hydrogen or oxygen gases by slowly squeezing the baggy until the water is displaced by the gases. The water will leave the pipette by slowly massaging the bulb end of the pipette while holding it upside down in the water container at about a 45º angle, which works best. The teacher must practice this technique several times before unleashing it to the students. Be patient, it will work! Draw some water into the stem - without this, the rocket will not fly far when "launched". Challenge your students to explain why the water will make the rocket go farther. You might want to talk about Newton's Laws of motion here, if you have time.
4. Slip the pipette rocket over a copper wire (12-14 gauge) that is grounded to Earth. The tesla coil needs to be able to jump a gap surrounded by the gas mixture and any current needs to travel to ground in order to be effective here. Remember that hydrogen is lighter-than-air! Never tip the gas-filled rocket open-end up - the gas will escape.
5. The ends of the copper wire lead must be above the water in the gas-filled region of the rocket.
6. With some water in the stem, launch the rocket by triggering a spark. DO NOT aim the rocket at anyone! If the water leaks out of the stem while positioning the rocket over the wires, immediately fill the stem again by holding the wires and rocket in a cup of water and drawing a very small amount of water into the stem. The rocket should fly up to 10 m!
7. Vary the activity by changing the ratios of gas mixtures, and or try cutting the tips of the pipettes to two or three different lengths. This activity could lead to several variable changes for students that want to learn more, or teachers too.
8. Students should be given a full class period to explore and practice filling and launching the rockets. More time is needed if you have several students, unless you have a lot of equipment. In my class, the teacher and the tesla coil are the limiting factors most of the time. Please read the teaching tips section to aid in the discussion and have your students complete the follow-up , introductory, assessment questions, and advanced assessment questions when through with this lab.
Clean-up and storage:
At the end of the experiments, wipe excess lubricant off of straw and pipettes. Clean all syringe parts (including the seal), caps and tubing with soap and water. Use plenty of soap to remove oil from the pipettes. This extends the life of the pipettes. 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.

Teaching Notes and Tips

As stated earlier, this lab requires a day or two of demonstrations, explanation, and practice to work out the kinks. The following are some tips to make life easier for the teacher.
This activity offers many variable and this can be very overwhelming; to the point where learning might be hindered. It is less confusing if you keep this activity to one variable at first. Try starting out with just an air mixture as a demonstration and discuss why nothing happens (a control). Mix 2-parts hydrogen with one part oxygen and show the best results. I have discovered this is one assignment where kids will want to try it after the demo. Students got bored when they were not successful after a couple attempts and or just gave up. Find a way to make every student or group successful by the second attempt. Once they figure it out, there is no stopping them. After everyone gets how to make their rockets work, rein them in and start the lesson. Once the lab actually starts, students need to document and collect data for every trial and record the gas mixture ratio.
Safety: Most students are afraid of the high voltage tesla coil because they see a huge spark when you arc across air to the copper wire to ignite the gas mixture. I zap myself as a demo to prove that you will be OK if you accidentally become the "short path" to ground. It stings just a bit, not much more. Make a human chain and try it, some students will take the challenge. I always have my students where safety goggles during this activity because flammable gases are being ignited and rockets are being discharged at fast rates. State Law requires that students wear safety goggles during this sort of chemistry lab activity.

Teaching tips:


1. Use large bulb plastic pipettes for the rockets.

2. Award prizes for the rockets traveling the greatest distances.

3. One objective of this experiment is to encourage students to try various mixtures of hydrogen and oxygen. They will empirically discover that the best mixture is 2 parts hydrogen and one part oxygen.

4. This reaction is used by NASA in their Saturn launch rockets.

6. The rocket idea comes from David Ehrenkrantz and John Mauch. Design for piezoelectric igniter is modified from a model developed by Bob Becker.

7. You may wish to generate a bag of hydrogen and oxygen for distribution to the students in order to save time in the laboratory.

Follow-up or Introductory Questions:


1. How far, in meters, did your rocket fly?

2. Why did you start by filling the rocket with water?

3. Which rocket would fly further: (a) a rocket filled with pure hydrogen; (b) a rocket filled with a mixture of hydrogen and air; (c) a rocket filled with a mixture of hydrogen and oxygen?


Assessment

1. How far, in meters, did your rocket fly?

2. Why did you start by filling the rocket with water?

3. Which rocket would fly further: (a) a rocket filled with pure hydrogen; (b) a rocket filled with a mixture of hydrogen and air; (c) a rocket filled with a mixture of hydrogen and oxygen?

4. Why must some water be left in the stem of the rocket in order for the launch to be successful?

5. What is the reaction occurring inside the rocket?

6. Which hydrogen-oxygen rocket is expected to fly farther, a rocket that is mostly filled with oxygen and some hydrogen or one mostly filled with hydrogen and some oxygen?

7. Would rockets filled with hydrogen and air fly at all?

Advanced Assessment Questions
8. What ratio of hydrogen to oxygen is optimal? Use a balanced chemical equation to answer this question.

9. Real rockets such as the NASA's Saturn launch vehicles use liquefied gaseous hydrocarbons and liquid oxygen for the rocket's first stage and liquid hydrogen and liquid oxygen for the second stage. What sort of design feature would keep liquid hydrogen and liquid oxygen from reacting until they are supposed to?

Assessment:
Using a plastic pipette and the proper mixture of hydrogen and oxygen gases, students will launch their rockets at forty five degrees and attempt to achieve a distance of ten meters. This is about the furthest I have been able to launch the rockets after a lot of practice. High level assessments could include comparisons between theoretical calculations using physics formulas used to evaluate projectile motions including rockets to actual data collected during the activity. Students would then expand their new knowledge by launching 2-liter pop bottles out in the football field at a later time if permitted. In either case, calculating the operating efficiency would be useful in understanding the rocket's optimal operating efficiency.

During the past rocket activities, no technology was used to understand rocket chemistry. This year, I plan on experimenting with Logger-Pro technology to analyze the exact amount of reactant gases using a spectrophotometer probe if possible. This tool provides students with a refreshing look at how technology is used to understand how to understand and analyze chemical mixtures and relate it to stoichiometry in the real world of chemistry and to measure science in society.

During the activity, using a rubric to assess gives important feedback to both the individual student and the student group performing the activity. Having high expectation from the beginning encourages student motivation and expectations of the rocket activity. As of last year, about 10% of the students that participated in this activity had successful rocket launches in my classes. This year I will put together a short video that we will watch that demonstrates the launch process and sequence that students can review during the activity. My goal would be to provide most students with an opportunity have successful launches. In the rubric, I will have each step of the process listed as an independent step. Student groups will be responsible for assessing each step on their own with teacher guidance and evaluations throughout the entire process. This in mind, it is important for teachers pursuing this activity to become very skilled at explaining the chemistry and understanding the operational mechanisms of the rockets before having students perform it.

Standards

The following standards have been adopted by the Minneapolis public school district and are directly aligned to the Minnesota state standards for high school chemistry and physical science, grades 9-12.
A. Structure of matter: The student will understand the nature of matter including its forms, properties and interactions.
16. The student will understand that the concentration of a solution may be expressed as molarity (M), percent by volume, percent by mass, or parts per million (ppm).
B. Chemical reactions: The student will describe chemical reactions and the factors that influence them.

1. The student will describe chemical reactions using words and symbolic equations, using IUPAC names.
4. The student will explain how the rearrangement of atoms and molecules in a chemical reaction illustrates conservation of mass.
6. The student will understand that the types of chemical reaction include synthesis, decomposition, single replacement, and double replacement, combustion, respiration and photosynthesis. (Predict the products only)
7. The student will use the mole concept to make stoichiometric predictions and limiting reactions.

References and Resources