July 4th was Independence Day here in the United States, a day full of celebration and fireworks. Why not have fireworks year-round and without the chance of getting burnt? Today we’re making fireworks in a beaker (or whatever clear vessel you have)!
Tall, clear beaker or glass filled 2/3 full with warm water
Water-soluble food coloring drops
Toothpicks or other stirring utensil
- Fill the bowl with 2-3 cm of oil. In the pictures, we show a beaker, but a bowl works much better. We noticed the smaller surface area of the beaker made steps 2 and 3 much harder, and the results were not as pretty!
- Drop food coloring onto the oil, being careful not to let the drops mix or clump together. We recommend using liquid food coloring in a dropper. If you are using gel food coloring, it is very important to dilute it 1:10 in water before adding it to the bowl.
- Using a toothpick or fork, stir the oil/food coloring briefly. This is very important as it makes the drops smaller and makes sure that the dye is completely surrounded by oil, not quite forming an emulsion.
Kelsey is stirring the food dye droplets in the oil to distribute them and break them into smaller droplets.
- Gently pour the oil into the beaker of warm water.
- Watch and enjoy your “fireworks!”
How does this work?
The oil is a non-polar, hydrophobic (water-hating) substance. The food dye is polar and hydrophobic (water-loving). When you drip it into the oil, it doesn’t truly mix, even when you stir it with the toothpick.
Remember, like mixes with like, or polar substances mix with polar substances. Since oil is nonpolar, it does not mix with the polar water. Once you pour the oil mixture into the water, the oil/food coloring emulsion floats to the top because oil is less dense than water, and will not mix. However, the dye, which is in aqueous (water-based) solution, will slowly sink through the oil as it is more dense. When the dye reaches the bottom, it will eventually break the surface tension, escaping from the oil. When this happens, the dye will disperse throughout the water, traveling outward to areas where dye is less concentrated to try to equalize the concentrations in the water.
Isn’t science beautiful?
Here are some modifications you can make to build hypothesis-driven experiments:
- Try the experiment with varying water temperatures., Ffor example, try ice water (with the ice removed), room temperature water, orand hot water. Does the temperature of the water change the fireworks effect? Why do you think this is?
- Add one part dish soap for every two parts of oil you use in this experiment. Try mixing the soap into the water, into the oil, or into both the oil and water. What happens? What properties does soap have that allows this to happen? (Hint: Look back to the Science ACEs Dye Races Lab!)
- Mix the food coloring into things other than oil, then pour over warm water as you did in this experiment. Interesting things to try: Soap (not diluted), whole milk, or corn syrup. What happened?
- Make the students build their own lab by asking them to find things they think are polar, nonpolar, high density, or low density.
What would you like to learn next, Science ACEs?
Biotechie is a third-year graduate student studying metabolism and cell biology. She is also the social media manager for Twitter @ScienceACEs and facebook.com/ScienceACEs. Her career goals include academic research as well as science education and advocacy. When she is not in the lab, she can be found reading, exploring the city, or baking awesome snacks for her fellow Science ACEs. Follow Biotechie on twitter @biotech_babe.