By Gina Malczewski and David S. Heroux
- Ask an adult for permission to do the activity and for help when necessary.
- Read all directions and safety recommendations before starting the activity.
- Wear appropriate personal protective equipment (safety glasses, at a minimum), including during preparation and clean up.
- Tie back long hair and secure loose clothing, such as long sleeves and drawstrings.
- Do not eat or drink food when conducting this activity.
- Clean up and dispose of materials properly when you are finished with the activity.
- Thoroughly wash hands after conducting the activity.
- Caution: hot liquids!
- Do not eat or drink any of the materials used in this activity.
- Don’t use extremely hot or extremely cold water.
Disposal: All solutions used in this experiment can be disposed of down the drain with running water. Unused Pop Rocks® candy can be disposed of in the trash.
Introduction of activity
Pop Rocks® is a very special brand of candy — first sold back in 1961! The sugary goodness of the candy coats little pockets of gas that are under pressure. That gas is released when you put the candy in your wet, warm mouth, and the sugar dissolves, allowing you to “taste the explosion!”
You can do an easy experiment with a package of Pop Rocks® to look at the ways temperature affects this process. This experiment also demonstrates how you, as a chemist, can use different ways to measure reactions. In this activity, you can use your eyes, ears, and nose to study how quickly the gas escapes the candy.
- 2 packs of Pop Rocks® candy, 0.33 oz (9.4 g) each
- 4 dry bowls or cups of similar size
- Two ½-cup (about 120 mL) measuring cups
- Cold and hot tap water
- Divide one pack of Pop Rocks® candy equally into two bowls that are at least 12 inches (30 cm) apart.
- Pour ½ cup (120 mL) of cold water into one cup, and ½ cup of hot water into the other.
- Quickly, and at the same time, pour the water over the Pop Rocks® in the two bowls.
- Record your observations for each bowl.
- After the bubbling slows down, stir each with the spoon and observe what happens.
- Seeing, smelling, and listening are all ways to observe what is happening. If you haven’t already done so, try the experiment again with your eyes closed! Focus on what you hear and smell. Be sure to record your observations.
Describe what you:
How does it work?
Pop Rocks® are sugar candies with tiny pressurized bubbles inside them filled with carbon dioxide gas. When you place Pop Rocks® in water, the sugar coating dissolves in water, and the gas and pressure are released. This also makes a popping noise, and leaves behind the sugar molecules.
You might think that a chemical reaction is happening, but this activity investigates a physical change, which is when molecules move around, but no new substance is formed. The sugar is dissolved in the water, but it is still sugar. You could find the sugar again if you carefully evaporated the water. Melting, freezing, and boiling are also physical changes.
Sugar crystals are made of many individual sugar molecules. Normally, sugar dissolves in water, because the water molecules interact with the individual sugar molecules and make them dissolve. Over time, the crystals seem to disappear, because they become too small to see. However, they are still there in a different form. Hot water has faster-moving molecules and causes the reaction to happen more quickly than cold water would.
Gina Malczewski, Ph.D. is a retired biochemist who worked at Dow Corning Corporation in Midland, Michigan.
David S. Heroux, Ph.D. is a Professor of Chemistry at Saint Michael’s College in Vermont, in Colchester, VT.
Pop Rocks® is a registered trademark of Zeta Espacial S.A. ACS is not affiliated with Zeta Espacial S.A.