When you drop an Alka-Seltzer tablet into a jar with oil and water, it sinks and dissolves in the water, making carbon dioxide gas. This gas forms bubbles that carry colored water up through the oil. When the bubbles pop at the top, the colored water falls back down. This up and down movement of bubbles and colored water looks like the lava in a lava lamp. This cool experiment shows how things like density make oil float on water, why water and oil don't mix, and how a chemical reaction can create gas.