Micro Mole Rockets
Student Laboratory Kit
Materials Included In Kit
Hydrochloric acid, HCl, 3 M, 250 mL Hydrogen peroxide, H2O2, 3%, 250 mL Yeast, Baker’s (active), 1 packet* Zinc, mossy, Zn, 100 g
Pipets, Beral-type, graduated, 60 Wood splints, 15 *Freshly prepare yeast suspension for each class.
Additional Materials Required
(for each lab group) Water Beaker, 250-mL Graduated cylinder, 10-mL Marker (permanent pen) Paper towels Piezo sparkers (optional)†
Rubber stoppers, to fit test tubes, 4 Safety matches Spatula Test tubes, 13 x 100 mm, 4 Test tube rack †See the Supplementary Information in the Extensions section.
Prelab Preparation
Yeast Suspension, 2%: Add 100 mL of lukewarm tap water to 2 g of active, dry yeast. Prepare freshly before use.
Safety Precautions
Hydrochloric acid is toxic by ingestion and inhalation and is corrosive to skin and eyes. Zinc metal dust may be present on the bottom of the mossy zinc bottle. Zinc dust is flammable; avoid contact with flames and other sources of ignition. Do not use zinc dust in this experiment. If zinc is dusty, rinse it with distilled water to remove the dust. Hydrogen peroxide is a skin and eye irritant. Avoid contact of all chemicals with skin and eyes and carefully clean up any spills. Wear chemical splash goggles and chemical-resistant gloves and apron. Remind students to wash hands thoroughly with soap and water before leaving the laboratory. Please consult current Safety Data Sheets for additional safety, handling and disposal information.
Disposal
Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. The waste solutions may be flushed down the drain with excess water according to Flinn Suggested Disposal Method #26b.
Lab Hints
- Enough materials are provided in this kit for 30 students working in pairs or for 15 groups of students.
- This lab should take approximately 50 minutes for students to complete. Many students may want to experiment, however, with different variables to see how far their rockets will travel.
- When cutting the pipet bulb and stem, discretion should be taken based on the method of ignition. The written procedure cuts the bulb to allow a 5-mm wide wire from a piezoelectric sparker to be inserted. If a different method is chosen, the bulb will need to be cut to best accommodate the ignition source.
- The loudness test is obviously arbitrary. Nonetheless, the results are remarkably consistent from class to class. Students tend to anticipate that the 3:3 mixture will be the loudest, and this could certainly bias their results. Encourage students to pop-test their mixtures in a blind and random fashion, and also to repeat all of the tests at least once. Have one student in the group collect a gas mixture, without telling the other student in the group what the gas ratio is. Let the “blind” partner do the pop-test and judge the result. The partners should then switch roles and repeat the process to collect a second set of data.
- The target at which the rockets are launched can be a bull’s-eye or goalpost drawn on the chalkboard or, better yet, an open box at one end of the room. Although the rockets are very soft and safe, students should avoid aiming the rockets at one another, and they should be reminded to keep their goggles on at all times. The rockets should not be scaled up. Do not attach any hard objects to the rocket.
- The concentrations of hydrochloric acid and hydrogen peroxide were selected to give an even rate of gas generation. The hydrogen gas generator will almost certainly slow down to an inefficient rate before all of the gas mixtures can be collected and tested. The oxygen gas generator tends to be a bit more constant and will probably remain active for at least 30 minutes. It is recommended, however, that each group prepare two gas generators for both oxygen and hydrogen in advance. That way, if one of the generators slows down, the group can easily switch to the other generator without losing too much momentum.
- Instruct students to use mossy zinc pieces and not zinc dust. Zinc metal dust may be present on the bottom of the mossy zinc bottle. Zinc dust is flammable; avoid contact with flames and other sources of ignition. Rinsing the mossy zinc with distilled water will remove most of the dust.
- Have students practice filling the bulb completely with water. Squeeze the bulb to remove as much air as possible, then fill with water. Turn the bulb upside down to remove the remaining air and again fill to the top with water.
- Manganese, manganese dioxide and potassium iodide may also be used as catalysts for the decomposition of hydrogen peroxide. In our experience, yeast provided the longest lived oxygen gas generator.
- If the first pop test does not work, wait about a minute and recollect the gas. The generating gas must first purge the air out of the test tube.
- Some students may wonder why pure hydrogen gives a positive, albeit very faint, pop-test result. Hydrogen by itself, of course, should not react. The slight popping sound occurs as hydrogen escaping from the bulb mixes with oxygen in the air. For each volume of H2 expelled from the bulb, an equal volume of air is drawn back in. Eventually, a combustible H2/O2 mixture is produced in the bulb and the flame backfires into the bulb.
Teacher Tips
- Why do the micro mole gas rockets travel considerably farther when some water is left in the bulb? It’s rocket science! The water gives the expanding water vapor produced in the reaction something to push against—it is a propellant.
- Review Avogadro’s Law before beginning this experiment. It provides the foundation for the experiment as written, namely, that the volume ratios of the gases are equal to their mole ratios.
- In schools where “micro mole rockets” have become a tradition, students look forward with anticipation to trying to beat the class and school records for distance traveled by a rocket. The gymnasium, after all, showcases track records, and the pool swim records—why shouldn’t the chemistry lab showcase micro mole rocket records? Streamlining the pipet-bulb rockets with fins and a nose cone greatly increases the distances the rockets will travel.
- A wonderful extension of this lab would be to run the reaction in reverse. Generate hydrogen and oxygen together via the electrolysis of water and demonstrate that the gases are indeed produced according to the stoichiometric mole ratio. Call, write or e-mail Flinn Scientific to request a complimentary copy of publication No. 10461,“Microscale Electrolysis.”
Further Extensions
Supplementary Information
Piezo Sparker/Rocket Launcher The piezo sparker/launch pad is quite simple to construct from an empty piezoelectric barbecue lighter (such as the Scripto™ brand “Aim-n-Flame”™). Most people tend to discard the lighter once the butane runs out, but the piezo sparking mechanism is still good and will last almost indefinitely.
- Cut a 10-cm length of double solid speaker wire (24 gauge) and spread the two wires apart at one end to make a Y shape.
- Strip about 1.5–2.0 cm of the insulation off the two split ends (see Figure 5).
{13869_Extensions_Figure_5}
- Place a small straw (use the same piece of pipet that was used for the gas generator nozzles) over the butane outlet nozzle in the tip of the lighter (see Figure 6).
{13869_Extensions_Figure_6}
- Now for the tricky part: Straighten out one of the two stripped ends and thread it into the butane nozzle hole. This may be a snug fit; twisting back and forth as you insert the wire helps it go in smoothly (see Figure 7).
{13869_Extensions_Figure_7}
- Lay the other stripped end along side the metal shaft of the lighter (see Figure 8), and wrap with 2–3 layers of electrician’s tape around the wire, leaving about 1 cm of wire exposed (see Figure 9).
{13869_Extensions_Figure_8}
{13869_Extensions_Figure_9}
- Bend over the end of this wire and wrap with two or three more layers of tape (see Figure 10). Use hot melt glue to fill in the area around the nozzle and to keep the wire from slipping out of the nozzle. This piezo sparker may be used instead of matches to test the explosive reactions of the oxygen and hydrogen gas mixtures.
{13869_Extensions_Figure_10}
- To use the piezo sparker as a rocket launch pad: Make a hole in the center of a film canister lid. Thread the protruding speaker wire through the hole in the lid, and hot melt glue it in place from behind (see Figure 11). The lid will serve as a launch platform and prevent some of the water from spraying the shooter. You’re finished!
{13869_Extensions_Figure_11}
Correlation to Next Generation Science Standards (NGSS)†
Science & Engineering Practices
Analyzing and interpreting data Planning and carrying out investigations Using mathematics and computational thinking
Disciplinary Core Ideas
MS-PS1.A: Structure and Properties of Matter MS-PS1.B: Chemical Reactions HS-PS1.A: Structure and Properties of Matter HS-PS1.B: Chemical Reactions
Crosscutting Concepts
Energy and matter Scale, proportion, and quantity Cause and effect
Performance Expectations
HS-PS1-4: Develop a model to illustrate that the release or absorption of energy from a chemical reaction system depends upon the changes in total bond energy.
Answers to Prelab Questions
- Write the balanced chemical equation for the single-replacement reaction of zinc and hydrochloric acid to generate hydrogen gas.
Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g)
- Write the balanced chemical equation for the yeast-catalyzed decomposition of hydrogen peroxide to generate oxygen gas and water. Note: Since a catalyst is not really a reactant or product, it is usually written over the arrow.
{13869_PreLabAnswers_Equation_1}
Sample Data
{13869_Data_Table_1}
Answers to Questions
- Draw a bar graph to illustrate the relative loudness produced by pop-testing various oxygen/hydrogen gas mixtures.
{13869_Answers_Figure_3}
- Explain the relative loudness of pure oxygen and pure hydrogen in the pop-test.
Pure oxygen does not produce a noise in the “pop-test.” Oxygen supports combustion, but is not itself combustible. Hydrogen produces only a faint pop as it combusts with the available oxygen in the air.
- Write a balanced chemical equation for the combustion reaction of hydrogen and oxygen to give water.
2H2(g) + O2(g) → 2H2O(l)
- Complete the following sentence to describe the number of moles of each reactant involved in the combustion of hydrogen: Two moles of hydrogen react with one mole of oxygen to give two moles of water.
When the reactants in a mixture are present in the mole ratio given by the balanced chemical equation, all of the reactants should be used up when the reaction is over. There will be no “leftover” reactants. However, if one of the reactants is present in an amount greater than its mole ratio, then that reactant cannot react completely, and some of it will be left over at the end of the reaction.
- Use the mole ratio of hydrogen to oxygen from Question 4 to determine what happens when various hydrogen/oxygen gas mixtures are allowed to burn. Complete the following table to indicate which reactant (H2 or O2) is present in excess, and how much of it will be left over after the combustion reaction is complete. Note: The second one has been completed as an example.
{13869_Answers_Table_2}
Note: Some students pick up on this concept right away, while others struggle. For those students who are having trouble visualizing the idea of limiting and excess or leftover reactants, an effective teaching method is to have them write down the parts H2 and O2 as symbols. Five parts H2 and 1 part O2 would look like this: H2 H2 H2 H2 H2 O2. Tell the students to cross off the symbols as they get used up in the reaction. But remember, they have to cross off two H2s for every O2 they cross off! In the above case, we would get:
{13869_Answers_Figure_4}
Hydrogen is present in excess and there are three parts left over at the end of the reaction.
- Which oxygen/hydrogen gas mixture produced the most explosive mixture? Explain why this mixture was most explosive.
The most explosive gas mixture contained two parts oxygen and four parts hydrogen. When this gas mixture was burned, there was nothing left over. It was the most efficient reaction, and thus the most explosive.
- Why do the hydrogen and oxygen gas mixtures in the collection bulb not react as soon as they are collected? Note: Consider the role of the match and the properties of gas molecules at room temperature.
Even if H2 and O2 are both present in a combustible ratio, and the H2–O2 collisions are occurring at a considerable rate, the collisions are generally not occurring with enough energy at room temperature to form the activated complex. The reaction, therefore, does not occur at a detectable rate at room temperature. The flame or piezo sparker provides extra energy, in the form of heat or electricity, that makes the gas molecules move faster and increases the collision energy when they collide. The “energized” gas molecules have sufficient energy to form an activated complex and enable the reaction to begin. The minimum excess energy that must be supplied in the form of a flame or other source of ignition is called the activation energy for the reaction.
References
This activity is from Flinn ChemTopic™ Labs, Volume 7, Molar Relationships and Stoichiometry; Cesa, I., Ed., Flinn Scientific: Batavia, IL, 2002.
|