Lava Lamp

Groovy baby! Get down and boogie with the funky side of science in this exploration of liquids, density and chemical reactions

Curriculum links

  • Science > Chemical Sciences > Year 2 > ACSSU031
  • Science > Chemical Sciences > Year 6 > ACSSU095

What you need

  • tall glass, glass jar or plastic cup
  • water
  • food dye
  • oil
  • Alka-Seltzer tablets (or other effervescent tablets)

What to do

  1. Fill glass ⅓ with water and add a couple of drops of food dye.
  2. Carefully float oil on top of the water, filling the glass to about 1cm from the rim.
  3. Break the Alka-Seltzer tablet into 4 parts and gently drop them into the glass.
  • Note: if you don't have any Alka-Seltzer tablets you can add a tablespoon of white vinegar to the water and then sprinkle a few teaspoons of bicarbonate of soda onto the surface of the oil.

What's happening?

Oil and water really don’t like each other; they don’t even mix (in containers and social situations). Oil is less dense than water and rests on its surface. The Alka-Seltzer tablets chemically react with the water producing bubbles of carbon dioxide gas. This gas is less dense then both the water and the oil and so will rise up through both liquids. When the gas bubble passes from the water into the oil it pulls a small amount of water with it. Eventually, when the bubble reaches the surface of the oil and pops, the water falls back through the oil, back to its friends, away from the rival oil blobs.

The chemical reaction that occurs when you drop an Alka-Seltzer tablet – or almost any effervescent tablet – into water is an example of an acid base reaction and is very similar to the reaction between sodium bicarbonate and vinegar (see the Balloon Blowout activity). Alka-Seltzer tablets contain 3 main ingredients – aspirin, sodium bicarbonate and citric acid. When you drop an Alka-Seltzer tablet into water the citric acid reacts with sodium bicarbonate and forms water, a salt, and bubbles of carbon dioxide gas. If you want to get fancy about things we can write this out as a chemical equation:

Citric Acid + Sodium bicarbonate → Sodium citrate + Carbon dioxide + Water
C6H8O7 + 3NaHCO3 --› Na3C6H5O7 + 3CO2 + 3H2O

Once the tablet hits the water it begins to react pretty quickly but why doesn’t the citric acid and sodium bicarbonate react when the tablet is dry? Well, in order for two chemicals to react they need to run into each other. The problem is, in their solid tablet form the sodium bicarbonate and citric acid are basically stuck in the one spot. When you drop a Alka-Seltzer tablet into a glass of water the sodium bicarbonate and citric acid begin to dissolve and can move around much more easily allowing them to come into contact and react.\

Did you know?

The chemical name for aspirin is salicylic acid and its use in medicine dates as far back as 3000 BC. It is has long been used to treat pain and fever, is also used to treat some forms of arthritis, coronary diseases and has even been linked to a reduction in the risk of developing various cancers.
Despite the obvious health benefits of aspirin, its nutritional value cannot be said to be overly high. However, this didn’t stop two women from Illinois in the U.S.A. surviving on nought else but 8 aspirin and 2 cough tablets when they got stuck for 2 days in an elevator in January 2008.