There’s a really cool experiment on Science Alert that I tried with the boys recently. It’s so easy and so visually impressive that it’s almost criminal to sit this one out. It’s not often that you come across an experiment that makes such an impact and doesn’t require any fancy materials or equipment…
Here’s what you need:
- a deep dish
- some full cream milk
- cotton bud
- dish washing detergent
- food dye
What you do:
- Pour some milk into the dish
- Add a few drops of food colouring
- Dip the cotton bud into the dish washing detergent
- Place the detergent tip of the cotton bud into the food dye and hold it
- Watch the reaction!
Milk is mostly water but it also contains vitamins, minerals, proteins, and tiny droplets of fat suspended in solution.
Dish soap, because of its bipolar characteristics (nonpolar on one end and polar on the other), weakens the chemical bonds that hold the proteins and fats in solution. The soap’s polar, or hydrophilic (water-loving), end dissolves in water, and its hydrophobic (water-fearing) end attaches to a fat globule in the milk.
The molecules of fat bend, roll, twist, and contort in all directions as the soap molecules race around to join up with the fat molecules. During all of this fat molecule gymnastics, the food coloring molecules are bumped and shoved everywhere, providing an easy way to observe all the invisible activity. As the soap becomes evenly mixed with the milk, the action slows down and eventually stops.
You can also tell the kids that this is the reaction that’s taking place whenever they wash their greasy hands with soap.
Watch the video
If you enjoyed that, you can try this modified version from the Crazy Russian Hacker using batter instead of milk: