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.