Expt 033 -- Water Rocket

A small plastic rocket is constructed from the bulb of a plastic transfer pipet with a wide stem. This bulb is filled with water, and then most of the water is displaced first with hydrogen and then oxygen. Electrodes are inserted into the device. A spark causes the mixture to explode and launch the rocket.

Background

Mixtures of hydrogen and oxygen can explode and release considerable energy. This energy may be used to launch a rocket. A contest will be held to see whose rocket can be launched the furthest. Several variables can be tested, including: ratio of H₂ to O₂; amount of water left in the rocket; angle of launch; etc.

Safety

• The gas generating systems are dangerous and should be approached very cautiously. Keep them in the catch trays under the hood. The amounts of explosive mixture must be kept small. The sparking device can deliver a painful shock. Hold the "cap" by its edge; hold the button end between the first and second fingers, by the edge around the button, and press the button with the thumb. Water from the rockets causes a mess. Wash spills with water, and dry with paper towels. Wear goggles and apron. Wash hands after the experiment
• Point the rockets at an assigned target area.

Procedure

1. Obtain a plastic rocket made by cutting all but 1 cm from the stem of a wide-bore plastic transfer pipet. Fill the bulb and stem completely with water. Go to the hydrogen generator at the hood. Insert the gas delivery tube from that generator high into the bulb and fill the bulb partly with hydrogen; remove when the desired amount has been added. Go to the oxygen generator at the hood. Insert the gas delivery tube from that generator high into the bulb and fill the bulb partly with oxygen; remove when the desired amount has been added.

   !!!Click here to See Movie.

2. Place the bulb over the bare wires of an electronic sparking device. A small amount of water must remain in neck of the pipet. Point at an assigned target area.

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3. Spark the mixture.

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4. Note and record all observations.
5. Mix volumes of oxygen and hydrogen in the ratio of small whole numbers(i.e. 1/1,1/2, 2/1, 1/3, etc.). Record the distance traveled for each mixture.
6. Use a sponge to wash up spilled water.
7. Wash hands.

Questions

1. A mixture of hydrogen and oxygen appears to be stable indefinitely until sparked. Account for this observation.
2. Predict the outcome of sealing the gas rocket tube around the sparking wires (so that water cannot escape).
3. Predict the outcome of using a mixture of CH₄ and O₂ in the rocket.
4. Explain the role of the water remaining in the pipet. Predict the effect of emptying all of the water before sparking the mixture.

Handout Makeup

Name ___________________________ Class _______

Teacher __________________________

SmallScale 033 Water Rocket

Watch the movies. Describe the reactions for production of oxygen and hydrogen.

Describe the reaction in the rocket.

Curriculum-

Use when discussion hydrogen, oxygen, combustion, redox, explosions, or the difference between thermodynamic stability and the rate of reaction. This experiment also works for applied chemistry classes.

Safety-

• This is a good experiment for students, but it requires significant attention to safety issues by the instructor. Go through all of the safety precautions, one at a time.
• The gas generating systems are dangerous and should be approached cautiously. Keep them in the catch trays under the hood. The amounts of explosive mixture must be kept small. The sparking device can deliver a painful shock. Hold the "cap" by its edge; hold the button end between the first and second fingers, by the edge around the button, and press the button with the thumb. Water from the rockets causes a mess. Wear goggles and apron. Wash hands after the experiment
• Creating a generator is a safety issue. Both gas generating reactions release heat -- and a tightly sealed, closed, gas generating system releasing heat and producing gas is a potential bomb. Be careful. First, be certain that the stopper of the dropping bottle device is open. Test this by filling with water and dropping liquid from it. If drops come slowly and require a great deal of pressure, either try a different bottle or use a hot wire to open the hole in the dropper a bit. For this purpose, it can be too small but it really can't be too big.
• Horseplay can cause trouble. Be certain that students launch rockets toward a launch area at the end of the room or in a vacant hall. Make sure that students do not launch rockets at one another.

Time-

Teacher Preparation: 15 minutes

Class Time: 30 minutes

Materials-

These solutions are estimated per station set up in the hood.

• 40 mL of 3 % H₂O₂ -- (Available from drug stores; use as delivered. Buy fresh.)
• 40 mL of 0.5 M HCl -- (Add 16.7 mL 3 M hydrogen chloride (HCl) to enough water to make 100 mL solution.)
• 2 mL of 0.1 M Fe(NO₃)₃ -- (Dissolve 4.040 g iron(III) nitrate nonahydrate (Fe(NO₃)₃•9H₂O) in enough water to make 100 mL solution.)
• 5 g of zinc (mossy zinc)
• Set up a station for collecting H₂ and O₂ in each hood. If you have one large hood you may wish to set up 2 stations in that hood. (See Lab Hints.)
• 2 50-mL plastic bottle with a screw-top plastic dropping device
• 2 stem from a calibrated plastic transfer pipet (with a tapered tip)
• Shallow tray
• piezoelectric sparking mechanism

Construct the sparking mechanism.

1. Cut a 50-cm length of intercom wire (Radio Shack #278-559). Select one end to prepare for attachment to the mechanical sparking device. Remove 10 cm of covering. Separate the two wires. Cut one wire so that it extends 4 cm past the covering. Strip one cm of the covering. Insert it into a suitably sized butt connector (Radio Shack #64-3036). Solder the end of the short wire to the butt connector.

   !!!Click here to See Movie. Click |> to advance slides.

2. Obtain a mechanical sparking device, usually from a kit used to spark gas mixtures in outdoor gas barbecue grills. (A hardware store selling gas grills is a likely source. For example, Universal Ignitor, Part # 4184681, CharBroil, P. O. Box 1240, Columbus, GA 31993.)
3. Slide the butt connector over the tip in the center of the sparking device.

   !!!Click here to See Movie. Click |> to advance slides.

4. Strip 6 cm of covering from the long wire. Wrap this stripped wire around the wire in the handle of the device. Secure the entire area from the button end to about 2 cm onto the unstripped wire with electrician's tape.

   !!!Click here to See Movie. Click |> to advance slides.

5. Turn to the other end of the wire. Remove 4 cm of plastic covering. Strip the insulation from about 2 mm of the ends of each wire. Use a sharp object or a red hot metal wire to create a hole in the center of the top of a file canister. (A nail heated in a flame with tongs work well.) Insert the wire through this top, pulling through some covered wire so that it fits snugly.

   !!!Click here to See Movie. Click |> to advance slides.

6. Press the button at the end of the device.

   !!!Click here to See Picture.

7. A small spark should span the gap between the wires at the other end of the device. If this device is held incorrectly or wired improperly, the person holding the device may experience a small but very noticeable electric shock.

Disposal-

Discard the spent H₂O₂ solution at the sink with a large volume of water. With water running, decant the liquid from the zinc into the sink. Wash the zinc with distilled water twice, and decant the wash into the sink.

Lab Hints-

• Perform this demonstration for the class. Fill a bulb 2/3 with hydrogen, 1/3 with oxygen, squeeze out the water, and mount on a support with a buret clamp. Bring a lighted match to the end. The mixture will explode rather loudly, and usually gives a blue flame. Use this to initiate safety discussions.
• Several devices have been suggested for generating and delivering gases. A 50-mL plastic bottle with a screw-top plastic dropping device works very well (for example, Flinn AP1695). Cut the stem from a calibrated plastic transfer pipet (with a tapered tip), and fit that over the top of the dropping device on the cap of the polyethylene dropping bottle. This stem fits snugly. The tip fits easily into the short stem of the 'rocket' bulb making admission of gas into the bulb straightforward.

  !!!Click here to See Picture.

• Creating a generator is a safety issue. Both gas generating reactions release heat -- and a tightly sealed, closed, gas generating system releasing heat and producing gas is a potential bomb. Be careful. First, be certain that the stopper of the dropping bottle device is open. Test this by filling with water and dropping liquid from it. If drops come slowly and require a great deal of pressure, either try a different bottle or use a hot wire to open the hole in the dropper a bit. For this purpose, it can be too small but it really can't be too big.
• Remove the top from a bottle. Fill the bottle about 1/2 to 3/4 with mossy zinc. Add 0.5 M HCl to fill the bottle to about 80% volume. Screw on the top. Attach the extending stem.
• Remove the top from a second bottle. Fill that bottle to about 80% volume with commercially available 3% H₂O₂. Add 2 mL 0.1 M Fe(NO₃)₃. Screw on the top. Attach the extending stem.
• Place the gas generators in a tray to collect water. Place these in a hood.

  !!!Click here to See Picture.

Answers-

Q1. A mixture of hydrogen and oxygen appears to be stable indefinitely until sparked. Account for this observation.

A1. Although the mixture is unstable, in the absence of some initiating factor (spark, catalyst) the oxygen and hydrogen react too slowly to observe.

Q2. Predict the outcome of sealing the gas rocket tube around the sparking wires (so that water cannot escape).

A2. Eventually the bulb will explode; if the rocket cannot move off the sparking device, an explosion that tears up the bulb is likely.

Q3. Predict the outcome of using a mixture of CH₄ and O₂ in the rocket.

A3. This mixture should work. As it turns out, the mixture may need to be on the lean side (more O₂ than stoichiometric) in order to sustain an explosion.

Q4. Explain the role of the water remaining in the pipet. Predict the effect of emptying all of the water before sparking the mixture.

A4. The water acts as a temporary launch pad. The expanding gas mixture from the explosion will escape quickly through the opening of the pipet. Most of the energy of the explosion will not be tranferred to the pipet.

CoopLearn-

This is an excellent activity for group work. The activity lends itself to healthy competition; which group can launch their rocket the furthest. Moreover, there are several within group divisions that are possible. One person can work on the launch angle. Another can work on the gas mixture ratio. Another can work on the amount of water, if any, to leave behind in the rocket. A competition of 3-person teams works very well.

Reference-

This experiment was first developed by Robert Becker of Kirkwood, Missouri.

Key Words 1-

dihydrogen, dioxygen, explosion, hydrogen, oxidation, oxygen, redox, reduction, rocket, water formation

Elements-

H O Fe Zn Cl