Splitting Water the Easy Way




Introduction: Splitting Water the Easy Way

About: The Oakland Toy Lab is a community-based wonder lab for students to build, tinker, explore, make, break, and learn! We are writing up engaging science experiences so that educators, parents, youth, and famil...

Water, of course, is a big part of many great things: you, milkshakes, and water parks to name a few. Even though the ubiquitous liquid is transparent, there's more to see inside. While some molecular bonds last a lifetime, we can break these ones apart with a battery and some thumbtacks in a couple of minutes.

Let's split some water.

  • What: Splitting Water the Easy Way
  • Time: well, hopefully slowly. We will need it to survive and stuff.
  • Time of Project: oh, got it. About 30 minutes.
  • Concepts: chemistry, physics, electronics
  • Cost: ~ $1
  • Materials:
    • 9V battery (others work, just longer set-up)
    • 2 Thumbtacks (metal)
    • 2 Plastic syringes (no needle, anywhere from 5-20mL)
    • Clear plastic cup
    • Salt
    • Food coloring (optional)
  • Tools:
    • Scissors

A NOTE: there are other electrolysis at home projects out there, so look around! I am writing this one up for two things that can often be more difficult but are easy here: the creation of the electrical current and the capturing of the gasses. Okay, back to doing the impossible with chemistry.

Step 1: Ummm...SPLITTING WATER!?

I know what you're thinking: who wants to get rid of water? I'm actually a big fan of the stuff personally, but in taking it apart we can learn about what makes it up. And don't worry, people have been doing this in some form or another since 1800 and things aren't so bad.

At this point in the text, you've come to a crossroads. You can check out some science blather down below in this step, or if you just want to break up water and not be bothered, head to the next step.

If you're still reading this part, here we go with the science stuff.


Water, as we know, is formed by two hydrogen molecules and one oxygen molecule, giving it its other name: H20. These bonds aren't forever, though. The single oxygen is holding on to these two hydrogen molecules by covalent bonds. This may seem super strong because the word sounds sciencey but these bonds can be overcome with about 1.23 volts of electricity.


This is where the battery comes in. If we apply a battery to water, well, not much happens. Pure water is, scientifically put, a sucky conductor of electricity. However, if we add a bit of salt to it, suddenly electrons can move much for freely. For comparison, seawater is about a million times more conductive than pure water.

While everyone gets all excited about the positive end of the battery (anode), it's really the negative end (cathode) that's adding all the electrons. With this negative force in the water, suddenly water starts to get tugged apart.

Passing Gas:

Water may look all balanced from the outside, but if you peer into it, it's not. When broken up, the oxygen hogs all the electrons (0 2-) while each hydrogen comes away missing theirs (H+). With a little electricity added, the water bonds start to split apart.

With the cathode having a negative charge around it, the positive hydrogen ions (H+) start hanging around. Get a pair together and it forms H2 in the form of hydrogen gas that goes bubbling to the surface. Over at the positive end, OH- ions are what's left over, which gets turned in to water, some extra free electrons, and oxygen gas, 02. These will also go bubbling to the surface. In fact, for a long time, this was the cheapest method of harvesting hydrogen gas.

If everything's going spiffy, because there is twice as much hydrogen than oxygen in water, and they both pair up to make H2 and 02 gas, you should get about twice as much volume of hydrogen gas than you do of oxygen. That's twice as much gas bubbling out of the negative end. That's what we're going to capture with the syringes.

If your brain doesn't hurt enough yet, head on over to the much more elegant explanation of what's going on at wikipedia.

Step 2: Cut Syringes

Time to catch some gas. Start by simply cutting off the tip end of both syringes so that they are open-ended cylinders. This will make it much easier for bubbles to float up into them, and for us to measure the amount of gas captured.

Step 3: Tack Up a Cup

Take two metal thumbtacks and push them through the bottom of the plastic cup. Space them out so that when they are placed on the 9V battery, one touches each terminal without touching each other.

With a single press-fit, they should maintain a water seal without needing any glue.

Step 4: Make a Solution

Pour in the unsuspecting water, and give it a color tint if you'd like as well. Add a little bit of salt for conductivity, and give it a stir. Try pressing the thumbtacks on the battery. What happens? Which thumbtack is producing more gas and why?

If you're not getting good gas build-up on the thumbtacks, try adding a little more salt or check your battery.

Step 5: Take Apart Molecules

Place the syringes in the water, and pull so that there is no gas in them at the beginning. Hold the syringes so one is over one thumbtack, and is over the other. Place the set-up on your battery, and in a little bit, gas should begin bubbling up. You are splitting water into gasses!

You should find the negative terminal (cathode) producing twice as much gas by volume. You can measure this by looking at the marks on the syringe and subtracting the new water level mark from the original volume of liquid. You are harvesting PURE HYDROGEN and PURE OXYGEN. Okay, maybe pure-ish. If you want to test them, hydrogen gas is highly flammable (see: hindenburg), and if a lit match is held near it, it will give a quick pop. Oxygen gas, on the other hand, helps other things burn faster. If you hold a match near that tube, you will see it burn brighter and even re-ignite from a smolder. (Thank you to all the great comments on this matter!)

For more resources on splitting water and other electrolytic reactions, check out this video.

Have fun, get electric, and as always, keep exploring.



  • Tiny Home Contest

    Tiny Home Contest
  • Creative Misuse Contest

    Creative Misuse Contest
  • Fix It! Contest

    Fix It! Contest

127 Discussions

I was quite surprised to read (incorrectly)that Oyxgen, like Hydrogen, was flammable. I was also glad to finally read some people finally commenting (correctly) that Oygen is NOT flammble. I'm always amazed at how many people get this wrong. I've gotten into many discussions which have turned into arguments regarding people saying Oxygen is flammable. When someone has electrolyzed water into Hydrogen and Oxygen, the common test for this is to take a burning splint of wood and put it up to the small test tube which has collected a very small amount of Hydrogen in it. It will go POP as it explodes. Then, a burning splint is blown out, but still glowing red, is put in the test tube containing the Oxygen. It will relight very brightly. Sometimes it will relight many times when blown out and reinserted. In one instance, I even spoke to a firefighter who swore up and down that Oxygen was flammable. I told him to go and TRY and ignite pure oxygen.

Oxygen is an oxidizer it HELPS other things burn but does not burn by itself. To the commenter that said it "makes" things burn, that is incorrect as well. It will "help" something burn but Oyxgen can not MAKE something burn that is not flammable.

14 replies

If oxygen was flammable, then our atmosphere would've burnt up a long time ago. That should be the only argument one needs.

Yep. If you look up a material safety data sheet for oxygen (as all good lab-rats do), it's noted that oxygen may cause or intensify a fire, and that it's an oxidizer.

On the other hand, the MSDS for hydrogen notes, among other things, that it's an extremely flammable gas, that it may form explosive mixtures with air, and that it burns with an invisible flame.

If oxygen was flammable, it'd be noted as such on the MSDS.

If oxygen is not flammable, then why are there signs in hospitals, oxygen in use highly flammable?

idk why some are saying it is not a danger for flamability, there is one, but its true a cigarette won't ignite it. A cigarette lighter on the other hand, I know for a fact will ignite it, and I will never forget the time my girlfriends mother, who was on permanent oxygen breathing treatment, accidentally turned her breathing tube into a dual nozzle pure oxygen torch, which she couldnt figure out how to extinguish. Fortunatelly all she lost was her curtains on the window and a bit of her blanket. She was a heavy enough smoker for me to be sure that a cigarette wouldnt be enough, disgustingly her "clear" oxygen breathing tubes were caked with nasty brown tar from constantly smoking with them on.

hey guys, liquid oxygen if flamable as a gas. If you use an oxygen machine that separates the oxygen to give you pure oxygen, it is not flamable.


I'm a little confused by your comment. There IS a real danger with smoking and using oxygen. I hope my comment(s) didn't give you the impression that I was saying that there wasn't a danger just because I said oxygen wasn't flammable. There is a real danger for people who use oxygen therapy and choose to smoke at the same time. In fact, I just replied to someone else and made it very clear in that post that there is a real danger to using oxygen therapy and smoking, and why. My comment was simply to point out the fact that oxygen itself isn't flammable. Many people believe that it is. I was just pointing out the distinction that it is not. In your example of using the cigarette lighter you can certainly light the oxygen tubing on fire with the cigarette lighter but it's only the tubing that's burning, not the oxygen. There are examples of videos online where people try to light just the tubing (no oxygen flowing) on fire and it barely burns. But, turn on the oxygen and it becomes like a blowtorch. It's simply the oxygen making the fire burn much more vigorously then it would by itself but the oxygen isn't burning. Again, if it was my comment that you think gave the impression that there wasn't a danger with oxygen use and smoking, I apologize.

I hope I didn't create that impression either. Interesting though, I get it now, just the tube burning, nowI will never know how she lit the tubing. Obviously anyone on oxygen treatment shouldn't be smoking, and not just because they might start a fire, but we couldn't convince her to stop. Thanks for explaining it so I could understand. I didn't know oxygen was inflammable, and you are right it looked much like a blow torch, always assumed the oxygen was burning.

No problem at all. It's a reasonable assumption to make especially with all the signs you see around oxygen use and storage. Couple that with an accident like someone starting a fire while on oxygen therapy and it's easy to assume it's the oxygen that burns. It is quite amazing how much larger the fire is when pure oxygen is introduced. I've seen videos where people have TRIED to light oxygen tubing on fire with just a lighter or even a small torch like a propane torch and it doesn't burn very well on it's own (if t all) But, add the pure oxygen and yes, it looks much like a blowtorch. As I mentioned before they make a device that fits inline with the oxygen tubing that stops fire from continuing to burn up the length of the tubing. I think something like this should be mandatory especially in home oxygen therapy use. This particular device is called Oxysafe. I'm not sure if there are other types/brands of this type of device. Here is a quick video showing such a device in use. https://www.youtube.com/watch?v=dMgJ91vBzWs

I guess I haven't paid much attention to whether the signs say "highly flammable" or "no smoking" or both or what. My guess is they have signs like that to keep people from using or having anything flammable around an oxygen rich environment. While Oxygen won't burn by itself it will make any existing fire MUCH worse. It will cause a small flame to flare up and be much larger. It "feeds" fire one of the thing it needs most to burn while not being flammable itself. Someone who is receving oxygen say through a nasal cannula (tube that runs under the nose) should never smoke for a copule of reasons. One if that oxygen tubing sould fall down if say, the person falls asleep the oxygen could start to be trapped within their clothing. Then, if they should drop the their cigarette, it could start their clothing on fire. The extra oxygen trapped within the clothing could cause their clothing to become an inferno very quickly. Also, the plastic that some/all oxygen tubing is made out of is flammable. If that plastic tubing should catch fire it literally becomes like a blow torch. Again, it's NOT the oxygen burning, it is the flame from the PLASTIC burning that is being fed by the oxygen thus turning what would normally be a small flame into a blowtorch like flame. There are some videos on Youtube that show just how flammable oxygen tubing can be WHEN there is oxygen going through it. By itself, it will hardly burn. But, run pure oxygen through it and it will light and burn like crazy. In addition, hospitals also have large tanks of oxygen along with probably miles of oxygen supply lines running throughout the hospitals. If there should be a fire (for any reason) those lines and those oxygen tanks could be a major hazzard in a building fire (by making the fire much worse).

There are some videos on Youtube where they set up a demonstration where the oxygen tubing is routed around a couch or chair in a living room type situation and the oxygen is turned on. They then set the oxygen TUBING on fire. Once that tubing is on fire, it burns like a blowtorch and It lights anything flammable in its path on fire. I believe they now have some special devices that they can put inline with the oxygen tubing that will stop such a fire if it should happen. I believe the flame only burns as far as one of these devices and then the flame is stopped so it can't burn along the entire length of the tubing. In my opinion such a device sould be mandatory on every piece of oxygen tubing used and certainly required on any tubing used for oxygen therapy in the home.
Here is one such video where it shows a length of oxygen tubing burining in a mock-up of home oxygen use like I described.
https://www.youtube.com/watch?v=6bXIhtXrRVA I hope links are allowed. If not and that gets edited out, just append watch?v=6bXIhtXrRVA to the standard Youtube link.

As you know O2 only assists the burning. It does not burn. Liquid O2 with a carbon bar is a useful comertial explosive used to make tunnels in Switzerland.

Whilst I you are right, the technical distinction could be overwhelming or difficult to understand for many people (especially non english speakers or very young readers) and generally Oxygen should be treated as a highly flammable substance. I would argue in this case to leave it as somewhat of a "Lie we tell children".

I was also quite surprised that I wrote it. Thank you for a great explanation in the process. :)

It was nice to see the technical corrections. However, there is one subtle error. All substances except Oxygen oxidize (rust) - they just very in the rate. This is part of the scientific belief for entropy. In other words, there are no non-flammable substances - none! Even gold, silver, and platinum, given tens or hundreds of thousands of years will eventually oxidize.

I wish you were my son's science teacher this year.

I wish you had been mine, any year.

(I guess you are, this year.)

I just learned something fun today! Thank you!!! Great job, and fun to show kids!:) A great way to make science INTERESTING:)

In reply to the fuel cell description; instead of exploding the hydrogen that is generated, can't it be burned in a controlled fashion and used in power plants just as natural gas is used, but with no pollution products.? How does the fuel cell consumption of hydrogen compare in efficiency to the use of hydrogen in a burn and steam cycle?

Hey, great tutorial!

Although it should be noted that whereas hydrogen is flammable, oxygen is not. It is a combustion agent which makes the burning (oxidation) of a fuel possible : you can prove that by exposing a match to the O2 syringe only, nothing should happen apart from the match burning brighter (that is if you don't have too many gas impurities such as Cl2).

Oh and for people who wondered, there is twice as much H2 as O2 created for a simple reason :

the global reaction involves 4 electrons and is : 2 H2O = 2 H2 + O2

the reaction at the cathode is 4 H+ + 4 e- = 2 H2

and at the cathode 2 O2- = O2 + 4 e-

You create twice as much H2 as O2 and they take up about the same volume, therefore the difference.