Yesterday my kids and I took to our garden to try our hand at making a lava lamp. This experiment isn't complicated, but gives you the chance to talk about a few science concepts - density and "states" (solids, liquids and gasses).
So that you're well armed with your definitions, here they are (in simple terms).
Density is literally just how dense something is - or in chemistry terms, how tightly packed a substance is (the ratio between mass and volume). Something that is very dense means its molecules are tightly packed together, like a metal. Something that isn't dense has molecules which aren't packed closely together, like the air around you!
Sometimes, you can put two liquids together, and because one is less dense it will float on the other. In this case, oil and water.
To do this experiment, you need
- a bottle (we used a 2L plastic bottle)
- any kid of oil (we used olive oil because it was in the pantry)
- water
- food colouring
- any kind of fizzing tablet (we used Aspro)
Step 1: Fill the bottle about a quarter full of water.
Step 2: Pour in some oil on top of the water, and watch as it separates from the water. Wait for it to settle. The oil is less dense than the water (and has a different polarity), so it floats on top! My kids gave it a red hot go to mix it up - but you can't get it to mix, and the oil will always float up.
Step 3: Drop a few drops of food colouring into the bottle. The food colouring is more dense than the oil, so the drops will sink down through it. The food colouring has the same density as the water, so when they meet they will mix, and the water will change colour. It's fun watching them drop down slowly through the oil and then disperse when they reach the water!
Step 4: Once the water has completely changed colour, drop in half of one of your tablets. As the tablet beings to dissolve it releases gas. The bubbles of gas "stick" to the water. The water and gas bubbles are less dense than the oil, so they rise to the top. Once they pop and release the gas, the water falls to the bottom again.
Step 5: Remember not to let anyone drink the water (especially if you use Asprin like we did), and don't use the oil again. Once the bubbles stop, you can keep adding tablets to re-start it.