Another exciting Saturday, this time donning lab coats and goggles to do some properly wet and messy, hands-on chemistry to get everyone interested. Tim Sangster kindly ran this workshop, with his two able assistants Gillian and Jon, and a few parent helpers.
We started off by talking about the molecules that make up water (polar) and oil (non-polar, hydrophobic), and what happens when you try to mix them together. We filled tubes with both, using pipettes to add the water, and looked at how they stayed separate even when stirred or swirled around.
Chromatography was next, with everyone using red and blue food colouring dissolved in water to make a dark purple mixture. We discussed whether there were new purple molecules in our tubes, or whether the red and blue were just mixing together to look like purple. Tim had brought along some solid-phase columns to test this theory.
First, though, we all enacted molecules running through a solid phase (SP) column, by pretending to be small red molecules (children), or large blue molecules (adults). We all walked in and out of each other to mix our purple solution, then entered the SP column. Tim had created a column out of two rows of chairs (solid phase), which the adults (large blue molecules) were attracted to and sat on (bound to), whilst the children (small red molecules) passed on and out of the other end. We had been separated out!
We went back to our experiment tables and added the purple food colouring mix to our real SP columns, then pressed the liquid through using a syringe. Everyone watched closely to see the solid phase filters filling up with blue dye, then the red colour dripping out at the bottom. An interesting extra step was using acetone (nail polish remover) to remove the blue dye from the solid phase into a different tube. Acetone was added to the columns and squeezed through by syringe as before, then the blue colour collected in a new tube. We were back to how we started, with red colour and blue colour as separate molecules, and from this we could tell that the purple colour had not been a new molecule, but a visual mixing of the red and blue molecules.
The last experiment was very exciting, and combined the oil/water demonstration with a colour to make a lava lamp! We took our large tubes of water and oil, and added a squirt of food colouring. We watched as this sank through the oil and joined the water layer to colour it. Into this we dropped half an effervescent tablet, which gave off bubbles of carbonate that dragged large blobs of coloured water up through the oil. These then burst at the surface, and the coloured water blobs then sank back through the oil down to the water layer, giving an effect very similar to that of a lava lamp for a few minutes. It was interesting to note the difference between the red coloured tubes (smaller molecule, sank more quickly into the water when added, gave frothier bubbles) and the blue (larger molecule, sank slowly down, gave larger blobby bubbles).
Everyone enjoyed themselves, and although there were plenty of food-colouring-stained fingers, we all felt we had learnt a lot and had fun doing it. Thank you Tim!
By popular request, here is how to create your own “lava lamp” at home:
What you need:
- Cooking oil
- Food colouring
- Effervescent tablets (e.g vitamin C tablets, containing calcium carbonate)
What you do:
- Find a thin, tall, transparent container for your experiment, e.g. a tall glass or small drinks bottle.
- Fill to about ¼ full with water
- Top up to about ¾ full with oil
- Add about half a teaspoon of food colouring, so the water is strongly coloured.
- Drop in a half or whole (depending on the size of your container) effervescent tablet.
- Enjoy the show!
- When the bubbles stop going, you can drop another tablet in to start it off again.