The 2021 National Chemistry Week theme is “Fast or Slow, Chemistry Makes it Go!” This theme makes us think of an engine where chemistry supplies the energy. In cars that run on gas, the energy that makes the car move is provided by the burning of gasoline. Many cars on the roads today are electric, however, and in the future all vehicles may be powered by electricity. Where will the electricity come from?
Wind turbines and solar panels are clean sources of electricity. They produce a lot of electricity when the wind is blowing or the sun is shining, and some of this electricity must be stored for future use. One way to store energy is to capture hydrogen gas (H2) and to later react it with oxygen (O2) from the air in a fuel cell. First, electricity is used to split water molecules into hydrogen and oxygen gas. When electricity is needed, the fuel cell then recombines the H2 and O2 to form water. Let’s look at electrolysis: the process of using electricity to split water molecules.
Materials
• Baking soda
• Battery, 9-volt
• Cardboard (large enough to cover the top of the glass)
• Glass
• Pencils (2) that can be sharpened at both ends
• Pencil sharpener
• Teaspoon
• Water
Be Safe!
Work with an adult to supervise or guide you.
Experiment
Fill a glass about half-full with water and add a teaspoon of baking soda. Stir until the solid dissolves. Sharpen both ends of two pencils. Place the top of the battery on the center of the cardboard and trace around the two circles corresponding to the (+) and (-) ends. Push a pencil through one of the circles on the cardboard, and a second pencil through the other circle. Place the pencil–cardboard assembly on top of the glass and gently push down on the pencils until the tips are completely underwater. Adjust the position of the pencils so that the battery ends can touch both pencil tips simultaneously. (See photo above.) Touch the top of the battery to the tips of the pencils. What do you observe? Do you notice any differences at the pencils connected to the (+) versus (-) ends of the battery?
What’s happening?
You should see bubbles forming at the tips of the pencils underwater. These are due to hydrogen and oxygen gas. The 9-V battery acts like an electron pump sending electrons through the pencils. (Although many people call it pencil “lead,” the core of a pencil is a special form of carbon called graphite, which is an excellent conductor.)
The ends of a battery are called electrodes. At the (-) electrode, H+ ions in water take up electrons and combine to form hydrogen gas. At the (+) electrode, OH- ions in water give up electrons to form oxygen gas, along with hydrogen ions (H+). By separating the hydrogen gas, you could convert it back to water inside a fuel cell, giving you the electricity to drive a car!
Questions to think about
Water is H2O, so we should see twice as much hydrogen as oxygen. What did you observe?
H+ and OH- ions involved in electrolysis are acids and bases, respectively. Add a few drops of red cabbage juice to the water and observe any color changes. Can you explain them?
Explore more at
https://www.thejoysharing.com/2019/07/electrolysis-of-water.html
https://orbitingfrog.com/2014/11/02/electrolysis-of-water-with-pencils-and-a-9v-battery/
To view more “ChemShorts for Kids” activities, go to:
https://chicagoacs.org/ChemShorts
