Water and oil don’t mix together because they have different molecular properties. Water is a POLAR molecule, meaning it has both a positive and negative end, while oil is NONPOLAR, meaning it doesn’t have any charged ends. The alka-seltzer tablet creates bubbles as it reacts in the water, creating carbon dioxide gas. All this together makes a mesmerizing lava lamp to observe! PS. If the effect stops, add another piece of Alka-seltzer to start it up again!