RSSHydrogen-Oxygen Bottle Rocket
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20: For Kids of All Ages, Page 90.
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Subscribers—read this article now in your digital edition!Use electricity to split tap water into hydrogen and oxygen gases, then use this explosive gas mixture to power a two-stage, electronically timed rocket.
Photos by Sam Murphy, Ed Troxell, Tom Zimmerman
Illustrations by Timmy Kucynda
Schematic Notes
Tom Zimmerman
December 12, 2008
CIRCUIT SUMMARY
The circuit consists of a 555 timer that outputs pulses at about one per second to a 4017 counter/decoder. The pulse rate is determined by the 1 M variable resistor, indicated by the flashing green LED connected to pin 3 of the 555 output. When the FIRE switch is closed the 4017 counter/decoder raises the output of one pin at a time, turning on in sequence the green, yellow and red LEDs, to provide a visual count down, then turns on transistor Q1 to fire stage one, followed by Q2 to fire stage two. If the rocket starts curving back to earth before stage two fires, decrease the variable resistance to speed up the sequence rate.
HOW TO LAUNCH
To launch open both the ARM and FIRE switch and make sure no LED is on. Connect the igniters to the circuit with alligator clips. When the rocket is on the launch pad and you are ready to launch, close the ARM switch and make sure the green sequence rate LED is flashing about once per second. Make sure the launch area is secure, yell "FIRE IN THE HOLE" (my favorite part), watch the yellow sequence LED go on, then run to safety. If after a minute the rocket doesn’t take off, walk back cautiously and turn off both switches.
| Part Label | Part Number | Description | Vendor Number |
|---|---|---|---|
| Q1, Q2 | BUZ72L | MOS Power Transistor | Jameco #209058 |
| U1 | LM555 | Timer | Jameco #27423 |
| U2 | CD4017 | Decade Counter/Decoder | Jameco #12749 |
The record for a multistage water rocket is 1,000 feet. Mine went under 100 feet because the fins were too small, not low enough on the bottle and didn't have a nose cone, so it tumbled. I also didn't optimize the mix of water, HHO gas, and air. I focused on making fuel (HHO gas) and reliably igniting multiple stages. I leave it to the readers to optimize the water rocket part, since many people have been working on those aspects.
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- Chemistry?
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I'm curious about the chemistry of this rocket. The article hinted a little bit about the electrolysis and the need to add sodium bicarbonate as an electrolyte. But can anyone add some insight as to why the water molecule will decompose when there is a voltage potential between the two electrodes? And can anyone offer a little more detail on what the voltage and amperage needs to be at to induce electrolysis? Thanks!Posted by Compgeek on November 08, 2009 at 17:07:33 Pacific Time
- Chemistry?
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Glad you are curious so let’s dive into some electrochemistry. Current is the flow of electrons (1 amp = 6.24 × 10^18 electrons per second). Current flows in a liquid through ions which are atoms that have a charge due to an unequal number of electrons and protons. Pure water has very few ions (about 2 pairs per billion molecules!).
An electrolyte is a molecule that dissociates (breaks into ions) when dissolved in water. The baking soda (NaHCO3) creates lots of Na+ and HCO3- ions enabling chemical reactions that exchange electrons, resulting in a flow of current through the solution. Voltage creates a force that pushes electrons through the electrodes and provides energy to drive chemical reactions.
The electrolyte ions also neutralize charges at the electrodes that would otherwise oppose the flow of current, i.e. H+ ions around the anode and OH- ions around the cathode. Finally the Na+ and HCO3- are not as electrochemically active (have less favorable electrical potential) than the H+ and OH- ions so H2 and O2 gas are formed. If you use NaCl (table salt) as an electrolyte, chlorine gas is formed instead of oxygen because chlorine is electrochemically more favored than oxygen.
Further reading;
http://www.science-projects.com/Electrolysis/eLysis.htm
http://www.crscientific.com/electrolysis.html
http://en.wikipedia.org/wiki/Electrolysis_of_water
http://en.wikipedia.org/wiki/Standard_electrode_potential
Posted by Tzim on November 10, 2009 at 16:38:00 Pacific Time
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