by STEM Scouts
This post is an edited version of an experiment write-up originally appearing on Science Kids.
Watch our experiment on the STEM Scouts Facebook page.
- A clear plastic bottle
- Vegetable oil (the cheaper the better)
- Food coloring
- Alka-Seltzer (or any other effervescent antacid)
- Pour water into the plastic bottle until it is about one quarter full. We recommend using a funnel.
- Fill the bottle the rest of the way with vegetable oil. Leave some air.
- Wait for the oil and water to separate.
- Add about a dozen drops of any food coloring to the bottle.
- Notice the food coloring will fall through the oil and mix with the water.
- Cut an Alka-Seltzer tablet into quarters and drop one of them into the bottle. Watch the reaction!
- When the bubbling stops, add another piece of Alka-Seltzer. Does it start going again?
How Does It Work?
Oil and water do not mix. The two separated from each other, with oil on top, due to its lower density than water. The food coloring also doesn’t mix with the oil well, falling through to the water.
The piece of Alka-Seltzer tablet you drop in releases small bubbles of carbon dioxide gas that rise to the top and take some of the colored water with it. The gas escapes when it reaches the top and the colored water returns to the bottom. Alka-Seltzer fizzes because it contains citric acid and baking soda (sodium bicarbonate). The two react with water to form sodium citrate and carbon dioxide gas–the bubbles that carry the colored water to the top of the bottle.