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
- 9V battery (others work, just longer set-up)
- 2 Thumbtacks (metal)
- 2 Plastic syringes (no needle, anywhere from 5-20mL)
- Clear plastic cup
- Food coloring (optional)
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.
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.