Electrolysis of Water, contributed by Japnidh Thakral
Water is an important part of our daily life, but you might know that water is made up of hydrogen and oxygen. According to the periodic table, these elements are gases at room temperature. So one might wonder: how do two gases bond to form a molecule that is somehow a liquid in room temperature? What if there was a way to split water apart and verify that it is made up of gases? Through some electricity, we can investigate that possibility.
- Glass of water (mostly full)
- Salt (about a spoonful or so)
- Small piece of cardboard
- Two traditional pencils stripped of their erasers (and a pencil sharpener)
- A 9V battery
- (optional) ruler
- (optional) wires with alligator leads
- Pour the salt into the glass of water and stir until dissolved.
- Cut the small piece of cardboard so it rests comfortably on the top of the glass
- Mark the distance between the two terminals on the 9 V Battery. You can eyeball it or just use a ruler to note it down.
- Mark a good spot just off center of your piece of cardboard and puncture it with your pencil. Mark another spot on the cardboard with a distance equal to the measurement of the distance between the battery leads and puncture it with the second pencil.
- Sharpen both pencils on both ends.
- Place the pencils about midway in their respective puncture holes. They should fit snug.
- Rest the pencil-cardboard piece on top of the glass so that two ends are in the water.
- Suspend the battery such that the pencil heads above the water hit once battery lead each
- (optional) hook some wires with the alligator clips from one lead of the battery to one pencil head and one with the other lead to a different head.
- Watch some physics!
Physics and Concepts
We should start seeing some bubbles form on the heads submerged in water, as one of them has hydrogen gas forming with the other being oxygen, for as long as the battery is being held on the top leads. Swapping the battery lead orientation yields no difference, but switches the gas orientation accordingly.
The concept that is being demonstrated is the inner chemistry of water. Ordinarily, water is created because hydrogen and oxygen do not have enough outer electrons, and when they bond, they share a set of outer electrons that they have already. By applying electricity, you make an excess of electrons on each end of the submerged pencils, and the charged hydrogen/oxygen gravitates to the opposite charged head. This way, the hydrogen and oxygen get separated. Then with the excess of electrons, the hydrogen and oxygen have enough electrons on their own to make their neutral gas form.
- Which head has hydrogen gas accumulated and which head has the oxygen gas accumulated to? Hint: the chemical formula for water is H20: two parts hydrogen and one part oxygen.
- How can you tell that the bubbles being formed are actually hydrogen or oxygen gas? Hydrogen gas is actually flammable, so is there a method you can think of to gather the bubbles and test it? (try using a test tube and a candle)
Congratulations, you split a water molecule! You now know that liquid water is made up of elements that are gases on their own. That’s pretty interesting. The exact reason why they end up being different states of matter is a bit more difficult to answer, but this lets you see the actual composition of water directly.