Water is a chemical made from two gases: hydrogen and oxygen. Every water molecule has two atoms of hydrogen for every one atom of oxygen. In chemistry, the formula for a water molecule reads as H2O. This chemical formula shows a bond between the two gases. Every water molecule has a stored amount of energy within its hydrogen and oxygen bond. When the bond splits apart, it releases energy that can be used to do work.
Splitting liquid water molecules into hydrogen and oxygen gases creates a lot of energy, which can be turned into electricity. Electricity can power the lights and appliances in a house. Electricity can also make cars drivable. Many things would not exist without electricity. Water power creates electricity, and it is because of its unique hydrogen-oxygen bond. To break the hydrogen-oxygen bond found in a water molecule, some amount of energy is needed to get the atoms in the water molecules active enough to separate. The process of splitting water molecules may be revealed in the chemical reaction known as water electrolysis.
Anybody can witness the effects and outcome of water electrolysis at home or school using a battery and water. Electrolysis describes a chemical change that takes place, especially in the form of decomposition, in an electrolyte by an electric current. The battery supplies this energy through its two terminals or poles, including positive and negative electrodes. When water connects to these terminals, the energy within the battery flows between the electrodes. As electricity passes through the water, it splits the hydrogen-oxygen bond found in the water. Electrolysis also occurs in the process of making metals, such as aluminum. Think of electrolysis the next time silver or gold-plated jewelry comes up in a discussion.
To observe the electrolysis of water, a small experiment can be done at home or school under the guidance of a parent or teacher. While the project itself is relatively safe, it is best to have somebody watch during the experiment to make sure it pans out the way it should. The project requires one 9-volt battery, two number 2 pencils, salt, cardboard, electrical wire, one small glass, and warm water. Remove the eraser and metal part on the ends of the pencils before starting the experiment. Sharpen each pencil at both ends. Next, cut the cardboard to the shape of the glass. It will need to cover it fully. After cutting the cardboard, push both pencils through the cardboard. Be sure to position the pencils one inch apart from each other. Pour warm water into the glass along with one teaspoon of salt. Allow the salt to dissolve completely. The salt helps conduct electricity in the water.
After dissolving the salt in the water, connect the electrical wire to the positive (+) side of the battery. Connect the other side of the electrical wire to the "lead" at the top of the pencil. Repeat these steps for the negative side of the battery, except by connecting the electrical wire to the second pencil top. Next, place the bottom ends of the pencil into the salted water. Electrolysis should start within a few minutes. Once the electricity passes through the electrodes or pencils, the water splits into hydrogen and chlorine gas. Small bubbles should collect around each pencil tip, which shows this split taking place. Hydrogen gas will collect around the cathode. The chlorine gas will collect around the anode.
The electrolysis of water in this experiment produces chlorine gas as a secondary reaction to the process of electrolysis. Water causes this to occur when salt is added to it. When adding salt to water, it causes the oxygen atoms to combine with the salt. This forms hydroxl ions not normally found in water. The chemical formula for salt is expressed as NaCl, or sodium chloride. As a result, chlorine gas releases around the pencil tip and not oxygen. The electrolysis of water in real ecosystems occurs by splitting hydrogen and oxygen without the secondary reaction, but it requires a higher level of electricity not found in a 9-volt battery.
Follow these links to learn more about the process of water electrolysis:
- Electrolysis: Obtaining Hydrogen from Water: The Basis for a Solar-Hydrogen Economy
- H2O Electrolysis: Splitting Water!
- HowStuffWorks: Electrolysis
- Electrolysis of Water Science Project