Inside: The Icy-Hot Christmas science experiment allows your kids to explore the concepts of hot and cold, water density, thermal energy, and even color mixing.
There are all sorts of science lessons you can teach your kids in the kitchen while cooking dinner.
The best part is that instead of trying to send your kids away to play somewhere else while you put a meal together, you can stay side by side, using your and their curiosity to create ideas.
Just remember that for this activity, you need to plan and freeze some green-colored ice cubes in advance. Then, on the day of the experiment, kids can do 99% of the work themselves as they separate red and green colored water by varying their temperatures.
Without any magic or tricks, the red-colored water will end up floating on top of the green water.
What does it mean?
This activity is basic science: hot water rises. But I bet it will spark the desire to continue experimenting with temperatures and colors. Perhaps 30 minutes or an hour later, your kid(s) will still be at a kitchen table (or floor) pouring water in and out of containers.
While doing the Icy Hot Christmas science experiment, your kids will
- Explore the concepts of hot and cold,
- Learn about water density,
- Observe molecules move (due to thermal (heat) energy),
- Enjoy color mixing and obtaining new hues, and
- Use scientific thinking to compare results and come to a conclusion.
Icy Hot Water Christmas Science
What you need
Red and green food coloring
PYREX glass storage container or something similar
Ice cube tray
What to do
1. Make green ice cubes
Fill an ice cube tray with water, and add one drop of green food coloring to each cube. Mix with a toothpick and freeze overnight.
We ended up using fancy round molds because all other molds were taken by other projects at just that time 🙂 Also, remember that frozen water expands! And if you don’t want to end up with a green mess all over your freezer (yep, guilty :), leave a bit of space in your molds for expansion.
2. Prepare red liquid
In a cup, mix 4 drops of red food coloring with 4 Tablespoons of hot water. You might be tempted to add more food coloring for a dramatic effect, but during our experiments, we discovered that more actually interferes with the purity of the experiment. More coloring means more dyes, more preservatives, and more density, which makes the liquid heavier and more likely to sink.
3. Mix red and green
Drop green ice cubes on one side in a container of water (room temperature is best). We used a 2.75 qt. Pyrex storage container. Then slowly pour the red hot water on the other side of the container. Pour away from the ice cubes!
Enjoy watching molecules move! It’s fascinating! You might notice that red dye moves and spreads much faster than green. It’s because the molecules in hot water move faster and collide with each more energetically due to increased thermal energy. Thermal energy is basically the temperature of the substance. The flow of thermal energy is heat.
Note that the glass containers are notoriously hard to photograph. When I used a camera flash (and even a regular flashlight) to capture clearly the reaction inside, the light bounced off the surface of the glass (the first pic below). And when I turned off the flash, then the glass walls made the liquid inside super blurry (the second pic below).
Does red water float above green water in your experiment as well? That’s because hot water is less dense than cold water!
Troubleshooting: If you have trouble seeing the color separation, use a flashlight.
The Science Behind Icy Hot Science
Why does hot red water float above the cold green water? That’s because hot water is less dense (lighter) than cold water. In this experiment, hot red water (just like hot air) rises, and cold green water sinks, that is until they become the same temperature and the colors mix.
But what does it mean to be less dense? Density measures how many molecules there are moving around in a space. That’s right, atoms and molecules don’t just sit there (unless it’s very, very cold…); they move around! And the faster they move, the more they bounce off each other and create space between them. And space, of course, weighs nothing.
The faster they move, the more space, the less dense! And what makes them move faster? Heat. The molecules in warmer substances move around more, creating space, expanding, and so becoming lighter.
If hot water rises and cold water sinks, then it’s logical that ice is supposed to sink to the bottom of the pond, right? Nope! This is the subject of our next investigation; stay tuned!