This week we are going to make a colourful milk display, like fireworks without the fire!
This activity is a great way to demonstrate emulsions, using washing up liquid as an emulsifier.
What you will need
- A baking tray
- Whole milk (it must be whole -any less fat and it won’t work)
- Washing up liquid
- Food colouring
1. Fill your baking tray with with milk
2. Add three/four drops of each food dye into the milk
3. Add drops of the washing up liquid on top of the food dye and watch what happens.
Safety: Do not drink the milk after (obvious I know but it has to be said)
What do you think of our milk display?
Why does this happen?
For this you need to think why we use washing up liquid in everyday? It is to clean our dishes and this break down the fat that makes them greasy. Fat is found in whole milk – milk is mainly small droplets of animal fat dispersed in water. The washing up liquid wants to do the same thing, break the fat down in the milk. We call it an emulsifier as it allows the water and fat to mix creating an emulsion. The emulsifier (the washing up liquid) molecules have a water loving head and a water hating tail. The tail sticks into the fat droplet and surrounds it leaving only the water loving heads. While it is doing that it scatters all the colour creating the display you see below. If you want to stretch your further, trying seeing if different washing up liquids have a different effect or alternatively try the test out in different shaped trays.
Try the activity again, but this time dip a cotton bud in milk and then lightly touch that to the surface of the milk. You should the same thing happens.