COMPOUNDS CAN BE SPLIT APART
 

The opposite of the element-combination process can occur with many compounds. Water is an excellent example. When water is electrolyzed, it separates into hydrogen and oxygen gases.
You can conduct the following electrolysis experiment at home. Make two electrodes out of large nails. Wrap some bell wire around each nail near the head. Add a cupful (a half-pint) of ordinary table salt to a bucket full of water, and dissolve the salt thoroughly to make the water into a reasonably good electrical conductor. Connect the two electrodes to opposite poles of a 12-volt (12-V) battery made from two 6-V lantern batteries or eight ordinary dry cells connected in series. (Do not use an automotive battery for this experiment.) Insert the electrodes into the water a few centimeters apart. You will see bubbles rising up from both electrodes. The bubbles coming from the negative electrode are hydrogen gas; the bubbles coming from the positive electrode are oxygen gas (Fig. 1). You probably will see a lot more hydrogen bubbles than oxygen bubbles.
Be careful when doing this experiment. Don’t reach into the bucket and grab the electrodes. In fact, you shouldn’t grab the electrodes or the battery terminals at all. The 12 V supplied by two lantern batteries is enough to give you a nasty shock when your hands are wet, and it can even be dangerous. If you leave the apparatus shown in Fig. 1 running for a while, you will begin to notice corrosion on the exposed wire and the electrodes. This

Fig. 1. Electrolysis of water, in which the hydrogen and oxygen atoms are split apart from the compound.

will especially take place on the positive electrode, where oxygen is attracted. Remember that you have added table salt to the water; this will attract chlorine ions as well. Both oxygen and chlorine combine readily with the copper in the wire and the iron in the nail. The resulting compounds are solids that will tend to coat the wire and the nail after a period of time. Ultimately, this coating will act as an electrical insulator and reduce the current flowing through the saltwater solution.