Lava lamps work by taking two substances that don’t mix (usually wax and water) and then heating it to make the ‘lava’ move around. This version doesn’t need wax or heat, just cooking oil, coloured water and a bit of chemistry.
You will need:
• 1 empty plastic bottle (500ml is a good size, still water bottles work best as they have a flat bottom!).
• Food colouring
• Oil (any vegetable oil will do)
• Fizzy tablets (soluble vitamin C, cheap versions from a pound shop are perfect!)
• Small light or torch (pound shop good for this too!)
• A tray to catch any spillages
First we need to assemble the lava lamp. Stand the bottle on the tray and half fill with water, pop a few drops of food colouring in until you’re happy with the colour. Next, pour in the oil, nearly up to the top (you might need a funnel and a grown-up for this bit!). Leave it to settle for a few minutes, when all the oil is at the top it is ready.
Now to make it move. Drop in a small piece of a fizzy tablet and watch what happens. You should see the bubbles carrying the coloured water up through the oil. You can stand the bottle (carefully!) on a small light or hold a torch underneath it for a real lava lamp effect.
If you want to keep it for another day you can put the lid on … but you MUST wait for it to stop fizzing first. If you put the lid on too soon gas will build up and it could be dangerous.
So how does this work? Oil and water won’t mix because oil is hydrophobic (this means it does NOT like water). The fizzy tablet reacts with the water to make carbon dioxide gas (just like the vinegar and bicarbonate of soda experiments). These bubbles of gas are less dense, basically lighter, than the oil so can bubble up to the top.