9 volt battery
Oxygen can be obtained from water by using a process called electrolysis, wherein an electric voltage applied to the water splits water molecules into molecules of oxygen and hydrogen, according to the equation: 2H2O + energy = 2H2(g) + O2(g); the "g" denoting that hydrogen and oxygen are gases. Although water is a poor conductor of electricity, an electric potential as small as 1.23 volts will initiate and sustain the electrolysis reaction.
Instructions
1. Add water to the dish to a depth of two inches and add the washing soda. Stir with the stick until all or most of the salt is dissolved.
2. Cut a piece from the foam tray about 3.5 inches long and 1.5 inches wide. Push each pencil through one long end of the tray, at a point about 0.5 inches from the end, so that they project 2 inches beyond the end, and are separated by the same distance as the battery terminals.
3. Set the foam/pencil assembly in the container, with the pencil ends in the water, and lean the assembly on the edge of the container.
4. Position the battery over the upper pencil leads so that they make a solid contact with the terminals. Fit the rubber band around the battery to secure its contact with the pencil leads. The battery must be above water level.
5. Note the activity at the bottom of the dish; you should see gas bubbles emerging from the pencil leads. If not, check to make sure the battery terminals have good contact with the pencil leads.
6. Fill a test tube with water. Stop the end of the tube tightly using your finger, then turn it upside down into the cup, releasing your finger when it is under water. The tube will remain full.
7. Position the tube over a pencil tip so that it captures the gas bubbles. Secure the tube in place against the container using the tape.
Repeat the procedure with the other tube.
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