Greetings Hydrogen lovers!
I know you are out there, even if hesitant to call yourself out as such... I know I was always fascinated by Hydrogen, or at least as soon as I realized how easy it was to generate that basic yet potent element - one that is capable of flying most everyday objects many meters up in the air just with the amount of material inside 1/50 cup of water. Ahhhh, the potential... Ohhhh, the danger... So, when I was about to give a class to my weekly science/makers 8th graders, their curriculum revolving around gases, liquids and atomic characteristics, it was bound to have electrolysis in it, and if electrolysis is concerned, why not build a nice Hydrogen rocket while at it? I mean, what could possibly go wrong? Well, historically, a lot. But these were other times, when people blindedly believed that technology will not only improve their lives but will save them from themselves. Luckily, today... ehhhh, well, let's change the subject. Dead Simple Hydrogen Rocket, did I say? Let's get to work!
Before proceeding, you should know that firing Hydrogen rockets can be dangerous. Be sure to take the necessary precautions and if in doubt, do not hesitate to write me. I do this with 8th-garders, but since I cannot personally supervise your build, I also cannot take responsibility for any injury caused during the preparation of this guide. Needless to say, Hydrogen is extremely inflammable and may lead to serious injuries when dealt with un-cautiously.
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Step 1: Materials & Tools
Plastic bottle (cap not needed)
Plastic box, about 1-2 liters in volume
30-60 cm thick ground wire, preferably copper, threaded
1-2 meters well insulated speaker wire (or, as far as you want to be from the launch site)
Screw terminal block, 2 terminals (usually comes in chunks of 12, though)
Rectangular piece of thick acrylic (8-10mm) that can fit into your box, flat
Scrap piece of styrofoam
Wire strippers or cutter
20-30V, 3-5 Amps power supply - either a lab power supply or a laptop charger
Drill and 10mm Drill bit
(or a laser cutter, if you have one)
Soldering iron and solder (optional)
Step 2: Electrolysis!
In this stage we will build the electrolysis device that will generate the Hydrogen needed to fuel our rocket. Basically, to save time & headache I use the same setup both for electrolysis and for the actual launching, more on that soon.
Start by preparing a salt water mixture - just add 5-6 tablespoons of salt to 2 liters of water and mix well.
Next, prepare the anode (oxygen) electrode: take a piece of the ground wire and twist it into a spiral, then place it inside the plastic box. Leave just enough wire to form a hook that will clip onto the rim of the plastic box.
Next comes the cathode (hydrogen) electrode: drill a 10mm hole in the piece of thick acrylic and stuff the hole with as many wooden skewers as you can, making sure that the skewers's dull end is aligned with the plane of the acrylic. Now take another piece of ground wire and tightly twist it around the wooden skewers starting from the acrylic plate and going upwards. Again, leave enough wire at the beginning so that after placing the acrylic flat inside the box, there will be enough wire to reach the rim and form a clip that will latch onto it.
That was quite a mouthful. See the diagram before proceeding!
Pour the salt water into your plastic box, making sure the electrodes are completely covered. if not, add more salt water or re-shape the electrodes so that they are completely covered.
Connect the electrode ends to a 20-30V, 4-5 Amps power supply. Make sure bubbles are forming next to the electrodes. Can you tell which electrode emits more bubbles? Can you think of the reason why?
Step 3: Ignition Electrodes
The ignition electrodes will be placed inside the plastic bottle that will gradually get filled up by Hydrogen. In the moment of launch, we will pass high voltage through them, which will create a small spark. This spark will ignite the Hydrogen, causing the rocket to take off...
Start by cutting 2 screw terminal blocks from the pack of 12, so that they remain connected. Connect the two speaker wires to these terminals from one side.
Cut two 2cm pieces of ground wire and attach them to the other end of the screw terminals. Bend the wire ends so that they are about 1cm apart (see image).
Cut a 1 by 2 cm piece of styrofoam and make sure it can fit your bottle. Next, attach it to the speaker wires using masking tape, just before the screw terminal. Connect the other end of the speaker wires to your gas grill igniter by soldering or just twisting the wires around the terminals of the igniter.
Test ignition electrodes by pressing the igniter and making sure a spark appears at the end of the cable, between the short ground wire ends. If no spark appears, the problem might be isolation-related: Separate the speaker wires from one another and retry. If still no spark appears, check the electrical connections in the circuit.
Finally, insert the electrodes into the bottle and secure the wire to the bottle with some masking tape.
Step 4: Moment of Truth
So, here we are at the final step...
Go outside. Seriously. You do not want to do this at home. Take an extension cord with you, for your power supply.
Place the plastic box on the ground and insert the bottle onto the skewers. Once the bottle is touching the water, gently press and release it so that salt water will be forced into it and the electrode wrapped around the skewers will be covered by salt water. If not covered, pressing the bottle harder to pull in more water.
Connect both electrodes to the power supply. Remember: the positive terminal gets connected to the anode, the electrode outside the bottle, while the negative gets connected to the cathode, the electrode inside the bottle.
Watch the bubbles steam as the solution gets muddier and muddier due to the disintegration of the electrodes, while contemplating on the amount of popularity this launch will most surely bring to your life. After about 3-5 minutes, depending on the Hydrogen generation rate, disconnect the power supply and get ready... connect the ignition electrodes to the grill igniter, making sure the bottle is facing upwards - you don't want it thrusting into your face - and press the trigger. Hydrogen should ignite, forming pressure inside the bottle, pushing water forcefully back into the plastic box, creating an opposite momentum (by Newton's 2nd law I think) causing your bottle rocket to reach sky-high altitude.
Depending on the amount of water, the width of the bottle nozzle and the amount of Hydrogen accumulated, the launch will probably make a notable sound (up to a gunshot, actually), and the bottle may reach anything from 20-200 meters. Be careful... the plastic bottle can take only certain amount of pressure, and over pressurising it might lead to raptures in the plastic, and consequently pieces of plastic shreds and sprays saltwater flying in high velocity in your radius. So, you may want to use protective goggles, rubber gloves, or any other means of protection.
Blast Away! Stay Safe!
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