Together but not mixed

“They are like water and oil”, is a phrase that you have surely heard, but do you know its scientific origins? Follow these steps and you will find out.

For this experiment you will need:
✔ Water
✔ a plastic container
✔ Vegetable oil
✔ 1 effervescent tablet such as Alka-Seltzer for a 16-ounce bottle (if the bottle is a liter, you will need 2 tablets)
✔ food coloring


Pour the oil into the plastic bottle until it is 2/3 full, then add a little water, leaving room at the top. Next, add 10 drops of food coloring. Do it one drop at a time and watch the color slowly sink to the bottom and spread out. Lastly, add the Alka-Seltzer tablet to the bottle.

⛔Warning: do not cover the bottle until the Alka Seltzer stops bubbling completely!


As you have seen, oil floats in water, this is because it is lighter or denser than water. Oil and water do not mix due to a phenomenon called “intermolecular polarity.” Intermolecular polarity basically means that water molecules are attracted to other water molecules, similar to magnets that are attracted to each other. Oil molecules are attracted to other oil molecules. But the structures of the water and oil molecules do not allow them to bond with each other.

When you added the tablet, it sank to the bottom and began to dissolve creating a gas known as carbon dioxide. This gas is lighter than water so it floats to the top. The gas bubbles attract some of the colored water and carry it to the surface. When the gas leaves the colored water, the water becomes heavy again and sinks. This happens over and over again until the tablet dissolves completely.

Variations: Change the temperature of the water and see if it affects the chemical reaction. You can also change the size of the bottle and see if it affects the number of bubbles produced. Use a larger number of tablets and see how it affects the reaction.