Piezo Ping Pong Popper

Introduction

Demonstrate piezoelectricity while performing this exciting micro-scaled explosion!

Concepts

• Piezoelectricity
• Combustion

Background

Piezoelectricity, defined as the change from mechanical to electrical energy resulting from stress, is found in everyday items such as watches, microphones, pressure gauges and grill lighters. Quartz, SiO₂, is a perfect example of how piezoelectricity works. Quartz is composed of silicon and oxygen atoms that are neatly arranged in rows throughout a crystal lattice. When pressure is applied to a quartz crystal, the oxygen ions, which are negatively charged, move in relation to the positively charged silicon atoms. The centers of positive and negative charges in the quartz crystal no longer cancel and a voltage occurs.

The piezoelectric lighter given in this kit does not actually contain quartz. Instead, it contains a ceramic piece that has been formed under an electric field which properly aligns the atoms during formation. When stressed, this ceramic piece can generate between 13,000 and 15,000 volts! The igniter holds the ceramic piece in a small plastic case along with a steel hammer that is attached to a spring mechanism. When the button of the igniter is pressed, the spring is compressed until it reaches a point where it releases the hammer. The hammer then rapidly strikes the ceramic piece. Piezoelectricity is generated, runs through the wires of the circuit and creates a spark between the small gap in the wires.

In this demonstration, the piezoelectric igniter will be used to burn ethyl alcohol in a small enclosed space—a ping pong popper. As the current enters into the popper and a spark forms, combustion of the ethyl alcohol–air mixture occurs. As the ethyl alcohol–air mixture burns, a large amount of energy is released due to the formation of carbon dioxide and water molecules. The energy heats the carbon dioxide and water vapor molecules that are formed in the initial reaction and causes the gases to expand. The expansion of the gases exerts a large amount of force on the side of the canister and lid. This force pops the top off the canister and launches the lid through the air.

Materials

Safety Precautions

Be very careful when performing this demonstration. Ethyl alcohol is a flammable liquid and a dangerous fire risk. Do not use more than 2 mL of ethyl alcohol. Do not substitute a more volatile liquid; many are dangerously combustible. Do not ignite the alcohol without the ping pong ball in place! Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Please review 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 piezoelectric apparatus may be used again and again. Excess alcohol may be disposed of according to Flinn Suggested Disposal Method #26b.

Procedure

1. Insert the “free” end of the lamp cord through the hole in the side of the ping pong popper approximately 1-inch deep.
2. Add 2 mL (~ 40 drops) of ethyl alcohol to the ping pong popper. Do NOT add more than 2 mL of alcohol to the canister!
3. Place a ping pong ball on the popper. Cup the popper in your hands and gently shake and warm. This will speed up the vaporization of the alcohol. Allow vapor to build up for a good 20 to 25 seconds.
4. Hold the popper in one hand and point it in a safe direction. Do not point the ball toward anyone! The ping pong ball can take off in strange directions!
5. Warn students that this apparatus may make a loud noise and that they should cover their ears.
6. Depress the button and away the ping pong ball goes!

Student Worksheet PDF

12013_Student.pdf

Teacher Tips

• This kit contains enough ethyl alcohol to perform the demonstration more than 25 times. Enjoy!
• A small flame may be present at the mouth of the popper after ignition. Extinguish the flame before repeating the demonstration!
• Be sure not to point the popper toward anyone at the time of ignition.
• The ends of the wire should be clipped occasionally to refresh the copper leads.
• Do not upscale this demonstration! Excess ethyl alcohol in a large container would be very dangerous!
• The demonstration may not be able to be repeated immediately. If there is excess CO₂ in the popper, there will be no combustion. Allow the ping pong popper to ventilate before repeating this demonstration.

Answers to Questions

1. Describe what happened in this demonstration.

   Ethyl alcohol was added to a “ping pong popper.” A piezolelectric igniter attached to the popper was initiated, and the ping pong ball flew out of the popper with a loud bang.

2. Write a balanced chemical equation for the combustion of ethyl alcohol.

   C₂H₆O(l) + 3O₂(g) → 2CO₂(g) + 3H₂O(g)

3. What is piezoelectricity?

   Piezoelectricity is the change from mechanical energy to electrical energy that occurs as a result of a stress. Piezoelectricity often occurs when some sort of pressure is applied to a material in which the ions are aligned a certain way. A forceful enough pressure causes the electrical charge in the material to change, creating voltage. One common material used in piezoelectricity is quartz, which is found in most watches.

References

Special thanks to retired teachers Walter Rohr and Lee Marek for providing this activity.