In our latest Science Club, the children made lava Lamps. They followed instructions carefully and tested different methods to work out which way had the best results. We first measured out water and added it to the bottle. Next we added 400ml of vegetable oil. After that, food colouring was dropped in with the option of glitter. The final task was to try out how much alka seltzer tablet had the best impact to create the lava. The children decided the lava lamps worked best with half a tablet and no glitter.
The science behind the fun
Oil and water do not mix. This is because the molecules that make up each one are more attracted to each other than they are to the molecules in the other substance. Oil is more viscous than water, but it isn’t as dense, so it floats above the water. The food colouring is water-based so it sinks to the bottom. When you add the tablets, they release carbon dioxide and these give the coloured water a piggyback to the surface. The bubbles burst, the gas escapes and the coloured water drifts back down to the bottom