Make your own colour changing paint and learn about acids and alkalis at the same time!
You will need :
- Red cabbage
- PVA glue or similar
- A pot
- Paint brush
- Citric acid (available online or at some pharmacies)
- Bicarbonate of soda
- Chop off some of the red cabbage ( about 1/8th is enough) and then cut this into lots of tiny pieces.
- Boil the cabbage for 3-4 minutes in a saucepan of hot water.
- Drain the cabbage water into a jug or pot and leave to cool. You want the water but not the cabbage so feel free to eat this!
- Put some pva glue into a pot or cup and pour in some of the cabbage water. Make sure it isn’t too runny.
- Use the mixture to paint a picture. If the colour doesn’t show up, try boiling the cabbage water again to make it more concentrated and then mix this with some new glue.
- Sprinkle some citric acid on top, what happens? It should go pink!
- Repeat with the bicarb of soda. Now it should go blue and may even fizz a little.
The Science Bit:
Cabbage water acts as a pH (how acidic or alkaline something is) indicator as it contains a water – soluble pigment called anthocynin. This makes it change colour when it comes into contact with a acid or alkaline solution. Citric acid (obviously) is an acid, and bicarbonate of soda is an alkaline, which is why they turn the cabbage glue different colours.
Why not try adding some vinegar or bicarb of soda to your cabbage water next time you are trying to feed the kids red cabbage! It could make red cabbage seem a lot more fun.