Oil and water don’t mix, which comes in handy for this fun science experiment! Play with density and chemical reactions when you try this foaming, bubbling experiment that uses an effervescent tablet like Alka-Seltzer to make carbon dioxide bubbles ooze up through a thick layer of oil. (Adult supervision required, since Alka-Seltzer contains aspirin.)
Fill a bottle 1/4 full with water or vinegar*. Add food coloring (or red cabbage juice) to the water or vinegar.
Fill the bottle almost to the top with vegetable (or other) oil. Note how the oil floats on the water, since it’s less dense.
Optional: Add cut-up plastic Easter basket grass, glitter, plastic beads, or other items you think might float on the water layer, but sink through the oil.
Finally, add an effervescent tablet to the liquid in the bottle and watch the chemical reaction. When the citric acid and sodium bicarbonate (baking soda) in the tablet react with the water and each other, they make something new: carbon dioxide gas, or CO2. The CO2 bubbles carry some of the colorful liquid up through the oil with them, but the dense liquid quickly sinks back down to the bottom.
*Vinegar reacts with the sodium bicarbonate the Alka-Seltzer, making extra carbon dioxide bubbles!
For a fun variation, put a balloon over the top of your bottle after adding the Alka-Seltzer to trap the carbon dioxide gas and inflate the balloon. If the balloon looks like it’s about to pop, remove it from the bottle.
Fill the jar about halfway up with water and add a few drops of food coloring for contrast. Add about half as much vegetable oil to the jar and watch it float to the top. Now, a spoonful at a time, add salt to the jar. The salt will pull some of the oil down with it, but will release the oil as it dissolves and the oil will float back to the top. This will make your science experiment look like a real lava lamp. Keep adding salt to make it keep working. Now, try adding sugar or even sand. Kosher salt worked really well!
What worked the best for you? Do you know why oil floats to the top of the water? Email me your answers in the comments section of this post for a chance to win a KITCHENPANTRYSCIENTIST.COM tee shirt (size M.) I’ll do a drawing for a winner in two weeks! Thanks to PBSkids/DragonflyTV’s website for this fun idea. Check out their website for more great kids’ science!