Here’s a quick experiment you can do to make a safe lava lamp in a bottle. Would be good when studying properties of materials or density.

You will need:

• Clear plastic or glass bottle with a screw cap lid
• Water
• Cooking oil – vegetable or sunflower
• Food colouring
• Antacid tablets – Alka-Seltzer or similar
• Torch (optional)

What to do:

Fill the bottle about a quarter full with water.

Add a few drops of the food colouring. (You could add some glitter too if you wish to make it sparkly)

Carefully fill the bottle almost to the top with the cooking oil. Leave it to settle and allow the two liquids to separate.

To make the lava lamp bubble – break up two antacid tablets and drop them in.

If you wish, hold a torch below the bottle to make it shine

Store the bottle with the lid on. When you want to use it again just drop more tablets in.

What’s going on?

Water is denser than oil, so it sinks below and the oil floats on top. The antacid tablets react with the water to produce bubbles of carbon dioxide gas. The bubbles rise up through the water and into the oil, taking some of the coloured water with them. When they reach the top they pop and the water falls back down to the bottom.