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Electrolysis is the decomposition of hydrogen and oxygen in water. In other words you break apart the molecules that make up water to restore the elements to their original state. In this case both hydrogen and oxygen exist in a gaseous state. In order to perform electrolysis you must run an electric current through water that contains an electrolyte. The electrolyte allows current to pass through the water because pure water, or even tap water for that matter, is not conductive enough to allow electricity to pass through it. The electrolyte I added in this experiment was salt, a common household item.
 
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Step 1: Getting the stuff

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The materials you will need for this experiment are:

baking soda (it used to be salt but then I was informed that I may have been producing chlorine gas)

Hot water (enough to fill your container of choice)

a container preferably air-tight and definitely clear

a pair of screws (these will act as the electrodes you pass the
current through)

a battery (a nine volt will do nicely for your first try)

Space to work (I barely had any and that made it a lot tougher)

Materials you may want to have, but are not necessary:

a glue gun (to patch up any holes left by the electrodes)

a DC power source so you don't have to worry about the batteries
running out.

a container that can dispense the hydrogen and oxygen (see introduction)

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werd608 says: Mar 12, 2013. 6:32 PM
Do I cut completely through to the other side
ubuntuPenguin says: May 18, 2011. 4:13 AM
is vinegar a good electrolyte to use? does it produce any dangerous gases?
buckminsterfullerene says: Sep 16, 2009. 1:11 PM
you shouldn't use screws, the metat that they are made of will probably short out the circuit and will oxidize. you should use carbon rods, you can see this in one of my upcoming instructables
tinstructable says: Dec 4, 2010. 12:48 AM
Platinum is the metal that you should use. Platinum's corrosive process takes much much longer than graphite, steel, etc. The industrial electrolysis machines use platinum for its non-corrosive properties.
Tombini says: May 21, 2010. 4:24 AM

You seem to love your carbon allotropes Mr Fullerene :P

El Mano says: Mar 10, 2009. 4:40 PM
Won't the screws corrode? I've made two good electolysis units that I had to scrap because my electrodes (pencil graphite and steel) corroded.
dragoonpreston says: May 26, 2010. 10:05 PM
The screws will corrode, but the point of this guide is to make a simple Electrolysis unit.

If you want something of a more permanent nature i would recommend getting Stainless Steel Tubing, it will cost more but it wont corrode.
Alpha2904 says: Oct 14, 2010. 10:17 AM
Stainless Steel will rust IF it can not dry. It will take longer but it will still corrode
Hightechk says: Sep 28, 2010. 5:09 PM
ty i was wondering what i was going to use
I Love Guns says: Feb 9, 2010. 2:45 AM
I'd rather use salt. Baking soda makes carbon monoxide instead. Not a good idea. The best electrolyte would be a weak acid or base (caustic soda or hydrochloric is good)
S3anyBoy says: Apr 7, 2008. 5:59 PM
I have a charger from my old laptop that outputs DC, but I don't know what would be negative and what'd be positive.
jamesmcelroy92 says: Jan 24, 2010. 4:39 PM
the negative one is usually black and the red is usually red, but if not just using water with salt put both the endsof the wire into the water and the one that has little bubbles coming of it will be the negative..lol.. but dont use pencils( only if you want oxygen aswell)  just use the copper wires but dnt leave them in for to long becasue they will corrode..
jamesmcelroy92 says: Jan 24, 2010. 4:39 PM
*the red is usually positive sorry lol
Tombini says: Oct 3, 2008. 7:17 AM
a simple solution (get it) is to set up the apparatus and check which one bubbles ~20 times more. This is the hydrogen
professorred says: Nov 14, 2008. 11:12 PM
fyi, there is 2 times as much hydrogen as there is oxygen. not 20.
Tombini says: Nov 15, 2008. 11:15 PM
Urrrghh, I meant by volume! Hydrogen is roughly 10 times less dense than oxygen, so if there is twice as much hydrogen you get 20 times in volume. I have done this test many times the hydrogen filled up a test tube and the oxygen was barely 1cm full
electricmic says: May 13, 2010. 10:04 PM
It is terrific that you are speaking from your actual experimental results. Right on! The molecular weights shouldn't matter- the volumes should be 2 parts Hydrogen to 1 part oxygen. That's why I love electrolysis- it is so intuitively clear (except when it doesn't work as expected). I think your large volumes of missing oxygen must have attached themselves to atoms from one of the electrodes.
electricmic says: May 13, 2010. 8:41 PM
The mass and size of individual gas molecules has no relation to the volume they occupy when flying around as a gas. Gasses are mostly empty space.  It's fascinating! check out the ideal gas law.

(Actually, all matter turns out to be mostly empty space if you could look closely- check out this link to Rutherford's experiment which measured the nucleus of gold atoms http://en.wikipedia.org/wiki/Geiger%E2%80%93Marsden_experiment)
Tombini says: May 21, 2010. 4:22 AM
You're right when it comes to volumetric analysis but I think there is a bit more to a gas than Avagadro's law or an "ideal" gas.  In reality all gasses have intermolecular forces which allow them to liquify and solidify, if there where no forces between these particles why would they condense?
This is where the definition of an "Ideal" gas comes in which is most closely related to Helium (If I remember correctly) because the only intermolecular forces are dispersion forces relating to the instantaneous positioning of electons in an electron cloud.

In gasses such as H2 and O2 (because of there lack of dipole moment) dispersion forces are also present but to a larger degree because of the larger size of the electron cloud and the number of electrons (shown by a higher melting point)

The other intermolecular forces of gasses include dipole-dipole and hydrogen bonding (I think).  Anyway both hydrogen and oxygen have low melting points proving the forces between them are negligable when looking at gasses at around 300 kelvins.
Default117 says: Mar 12, 2009. 3:45 PM
To correct you on your math: if you were going by densities, then there would be two Hydrogen atoms and One Oxygen atom (if you were to split a single water molocule). The two Hydrogen atoms would equal one fifth of the Oxygen atom.
Tombini says: Mar 14, 2009. 11:15 PM
Lol, smartypants... still the basic rule applies, whichever bubbles more is the Hydrogen
marmique123 says: Feb 9, 2010. 1:47 AM
aww... my friends said that its just boiling water... not hydrogen gas >o<
tinstructable says: Dec 4, 2010. 12:50 AM
Your friend doesn't know what they're talking about. It's hydrogen.
Default117 says: Mar 15, 2009. 10:25 PM
Yeah... I mean no... I mean... Aww crap Your making me think XD
ReCreate says: Mar 18, 2009. 7:36 PM
{{{ }}}
brain explodes
bylerfamily says: Aug 13, 2009. 6:16 AM
brain explodes.
ReCreate says: Aug 13, 2009. 4:19 PM
Much better
bylerfamily says: Aug 14, 2009. 10:04 AM
Yeah.
ReCreate says: Aug 14, 2009. 11:23 AM
:D Wow look [http://www-jpc.physics.ox.ac.uk/home_status.html JPC] can now boot Graphical linux distros!
ReCreate says: Aug 15, 2009. 4:16 PM
I forgot that code does not get executed in monospaced text XD
nodrog19 says: May 1, 2009. 7:27 PM
Equal amounts (by the mole) of gas at the same conditions have equal volume. You will get 2 volumes of H2 and one volume of O2. Look up the ideal gas law.
wiebevandomburg.hotmail.com says: Jun 21, 2009. 2:00 PM
yep , 22,4 liters of gas / mole
professorred says: Jun 27, 2009. 10:54 PM
Moles are furry and cute.
digital01 says: Jul 7, 2009. 9:06 PM
No they are curry and fute
professorred says: Aug 13, 2009. 10:38 AM
MMmmm. Mole curry.
ReCreate says: May 1, 2009. 7:38 PM
Everything now explodes,including brains
marmique123 says: Feb 9, 2010. 1:50 AM

hahahahhahahahaha!!

beavercleaver says: Jul 24, 2008. 2:39 AM
One output wire will have a white stripe or dashes on it, that is your positive. You seriously need a DVOM, they are really cheap, and necessary for any electrical experiments.
tinstructable says: Dec 4, 2010. 12:52 AM
Actually, a white striped wire usually indicates a negative, and dashed indicates positive. It took me a long time to figure that out when I couldn't figure out why all my projects wouldn't work.
beavercleaver says: Dec 5, 2010. 8:11 PM
Not in the automotive electronics world, dashes do not exist on wires. A DVOM is the only way to be sure what you are working with.
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