Piezoelectric Effect

Experiment Introduction

This experiment demonstrates the principles of jet propulsion through the explosive combustion of hydrogen obtained by water electrolysis and chemical reactions with metals. We'll use the bulb of a Pasteur pipette as a rocket, marking it to measure flight distances and compare the efficiency of different gas mixtures. Hydrogen generation will be performed through two methods: water electrolysis and reaction of metals (aluminum and zinc) with water. Oxygen will be obtained from hydrogen peroxide decomposition. The resulting explosive mixture will be ignited with a piezoelectric lighter to propel our improvised rocket.

Theoretical Foundations

Hydrogen Generation

1. Water electrolysis:

2H₂O(l) → 2H₂(g) + O₂(g) At the cathode (negative electrode): 2H⁺ + 2e⁻ → H₂ At the anode (positive electrode): 2OH⁻ → H₂O + ½O₂ + 2e⁻

2. Reaction with aluminum:

2Al(s) + 6H₂O(l) → 2Al(OH)₃(s) + 3H₂(g) Aluminum displaces hydrogen from water, especially in the presence of catalysts.

3. Reaction with zinc:

Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g) Zinc reacts more vigorously in acidic medium.

Oxygen Generation

Hydrogen peroxide decomposition:

2H₂O₂(aq) → 2H₂O(l) + O₂(g) The reaction is accelerated with catalysts like MnO₂ or heat.

Explosive Combustion

Combustion reaction:

2H₂(g) + O₂(g) → 2H₂O(g) + energy This reaction releases 286 kJ/mol, providing the energy for propulsion.

Propulsion principle:

According to Newton's third law, the rapid expulsion of hot gases backward generates an equal and opposite force that propels the rocket forward.

Materials and Reagents

Laboratory Materials

• Pasteur pipettes: To create the rockets (use only the bulb)
• Electrolysis source: 9V battery and electrodes
• Small containers: For collecting gases
• Syringes: For transferring gases and liquids
• Piezoelectric lighter: For safe ignition
• Ruler or meter: For measuring flight distances
• Permanent marker: For making marks on pipettes

Reagents

• Distilled water: For electrolysis
• Sodium sulfate (Na₂SO₄): Electrolyte to improve conductivity
• Aluminum powder or shavings: Hydrogen generation
• Granular zinc: Alternative hydrogen generation
• Dilute hydrochloric acid (HCl 1M): To activate reaction with zinc
• Hydrogen peroxide (H₂O₂ 3%): Oxygen source
• Manganese dioxide (MnO₂): Optional catalyst

Safety Equipment

• Safety goggles
• Nitrile gloves
• Laboratory coat
• Ventilated area or outdoors
• Safety fire extinguisher

Experimental Procedure

Rocket Preparation

Prepare the pipettes:

Cut the thin end of the Pasteur pipettes, keeping only the bulb Make marks every 1.5 cm on the outside of the bulb with marker Number the marks to facilitate distance measurement Check tightness: The bulb should be able to retain gases temporarily

Hydrogen Generation by Electrolysis

Preparation steps:

Dissolve a pinch of Na₂SO₄ in 100 mL of distilled water Pour into a small container Connect electrodes to a 9V battery Submerge electrodes in the solution Observe hydrogen bubble formation at the cathode Collect gas in inverted container submerged

Hydrogen Generation with Metals

Zinc method:

Place zinc granules in a test tube Add HCl 1M drop by drop Collect the generated hydrogen

Aluminum method:

Mix aluminum powder with water Add a few drops of NaOH to activate the reaction Collect the released hydrogen

Oxygen Generation

Catalytic decomposition:

Place hydrogen peroxide in a container Add a pinch of MnO₂ as catalyst Collect the oxygen released in bubbles

Mixture Preparation and Launch

Fill the rocket:

Submerge the pipette bulb in water Aspirate hydrogen from the chosen source (electrolysis, Al or Zn) Add oxygen from hydrogen peroxide until filling 3/4 of the bulb Leave a small air chamber

Perform the launch:

Place the rocket horizontally on a smooth surface Bring the piezoelectric lighter close to the opening Activate the spark to ignite the mixture Observe the flight and measure the distance reached

Data recording:

Note the type of mixture used Measure and record the flight distance Repeat the experiment 3 times for each mixture

Results Analysis

Efficiency Comparison

Differences in performance are expected according to the hydrogen generation method:

• Zinc + HCl: Produces hydrogen quickly, purer mixture
• Aluminum + H₂O: Slower reaction, may contain water vapor
• Electrolysis: Very pure hydrogen, but smaller volumes

Factors Affecting Performance

• Gas purity: Purer mixtures explode with more energy
• H₂:O₂ ratio: The stoichiometric relationship 2:1 is optimal
• Total volume: More gas means more available energy
• Temperature: Hot gases expand more when exploding

Measurement and Calculations

Average distance calculation:

Average distance = (d₁ + d₂ + d₃) / 3

Relative efficiency:

Efficiency = (observed distance / maximum distance) × 100%

Safety and Precautions

Experiment Risks

• Uncontrolled explosion: The H₂/O₂ mixture is highly explosive
• Fragment projection: Pipette debris can be ejected
• Burns: Hot gases can cause injuries
• Gas inhalation: Avoid breathing combustion products

Mandatory Safety Measures

• ALWAYS perform in open space or very ventilated area
• Use ALL indicated personal protection
• Keep people at least 3 meters away
• Have fire extinguisher or water available
• Never exceed 1 mL of gas mixture per test
• Never direct the rocket toward people or fragile objects

Emergency Procedure

1. In case of accident, evacuate the area immediately
2. If there's fire, use CO₂ extinguisher or sand, NEVER water
3. For minor burns, apply abundant cold water
4. Immediately notify the teacher or person in charge

Scientific Principles Demonstrated

Chemistry

• Electrolysis: Decomposition of compounds by electricity
• Metal reactivity: Metal activity series
• Redox reactions: Electron transfer
• Catalysis: Acceleration of chemical reactions
• Combustion: Exothermic reactions with oxygen

Physics

• Newton's third law: Action-reaction principle
• Momentum conservation: System momentum
• Thermodynamics: Conversion of chemical energy to kinetic
• Fluid mechanics: High-speed gas expulsion

Applications and Extensions

Technological Applications

• Space rockets: Similar propulsion principles
• Jet engines: Gas expulsion for propulsion
• Hydrogen production: Fuel of the future
• Fuel cells: Clean electricity generation

Experiment Variations

• Try different gas proportions
• Use different catalysts to generate oxygen
• Measure flight time in addition to distance
• Study the effect of launch angle
• Compare with other combustible gases (methane, acetylene)

Educational Conclusions

This experiment spectacularly integrates fundamental concepts of chemistry and physics, showing how chemical reactions can be converted into mechanical energy. Gas generation by different methods allows comparing efficiencies and understanding chemical reactivity principles. Quantitative distance measurement using marks on the bulb adds scientific rigor to the experiment, allowing statistical analysis and objective comparisons between different experimental conditions. Finally, strict safety measures teach the importance of responsible handling of dangerous substances and careful planning in high-energy experiments.