Procedure​

1. Remove the label from an empty 1 L (32 oz.) bottle

2. Add water until the bottle is about 1/3 full (about 12 oz. or 1 1/2 cups)

3. Add food coloring into the bottle and shake to make the color of the water uniform.

4. Repeat step 3 until the desired color is obtained.

5. Fill the bottle the rest of the way with vegetable oil (about 16 oz. or 2 cups) until about 3 inches from top.

6. Break the effervescent antacid tablet into pieces and slowly add some of the pieces into the bottle.

7. Let the tablet pieces sink into the water, bubbles should immediately develop, causing the colored water to move through the oil layer

8. A single tablet will last XX minutes, additional tablets (one at a time) can be added after the bubbling stops.

Optional

1. The bottle can be placed on top of flashlight in a dark room for a "lava lamp" effect

What is going on?

Water and vegetable oil are two liquids that do not mix (immiscible) when added together. The density of water (1.0 g/mL) is greater (heavier per a given volume) than the density of vegetable oil (~0.93 g/mL) leading to the water layer being at the bottom of the bottle. 

 

An effervescent antacid tablet contains aspirin, sodium bicarbonate, and citric acid. When the effervescent antacid tablet mixes with water, the citric acid dissolves and reacts with sodium bicarbonate to generate carbon dioxide (CO2) and sodium citrate.

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The formed carbon dioxide gas produces bubbles, which carry small amounts of water and food coloring with it as the bubbles rise through the vegetable oil. Once the bubble reaches the top of the vegetable oil, the bubble breaks, releasing the gas and causing the  colored water to sink through the vegetable oil until the colored water rejoins the water layer.

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Clean Up

Upon completion of the experiment, the oil and water mixture can be flushed down the toilet or poured down the drain, followed by running hot water for two minutes.

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