Moving Milk

Learning Intention:
I am learning....
• the effect detergent has in milk.

Success Criteria:
I will know I can do this when I am able to....
• explain why the milk moves.
• talk about the different types of milk.


Prerequisite learning activities:

Making Better Sense series:


Building Science Concepts series:

Other resources:
Click here to access and view online an experiment and video describing the experiment


Or click on this totally unrelated video to Watch the lost generation a play on words, which was inserted to see how movies look off line.



HOW DO I GO ABOUT THIS??

Materials
• Blue top milk
• Saucer
• Food colouring (red, yellow, green, blue)
• Dishwashing soap (Sunlight brand works well)
• Cotton buds
Experiment

1. Pour enough milk in the saucer to completely cover the bottom and allow it to settle.

2. Add one drop of each of the four colours of food colouring - red, yellow, blue, and green - to the milk. Keep the drops close together in the centre of the plate of milk.

3. Find a clean cotton bud for the next part of the experiment. Predict what will happen when you touch the tip of the cotton swab to the centre of the milk. It's important not to stir the mix just touch it with the tip of the cotton bud.

4. Place a drop of liquid dish soap (the Sunlight brand works well) on the tip of the cotton bud. Place the soapy end of the cotton bud back in the middle of the milk and hold it there for 10 to 15 seconds. Look at that burst of colour!

5. Add another drop of soap to the tip to the cotton bud and try it again. Experiment with placing the cotton bud at different places in the milk. Notice that the colours in the milk continue to move even when the cotton bud is removed. What makes the food colouring in the milk move?


How does it work?
Milk is mostly water but it also contains vitamins, minerals, proteins, and tiny droplets of fat suspended in solution. Fats and proteins are sensitive to changes in the surrounding solution (the milk).

When you add soap, the weak chemical bonds that hold the proteins in solution are altered. It's a free for all! The molecules of protein and fat bend, roll, twist, and contort in all directions. The food colour molecules are bumped and shoved everywhere, providing an easy way to observe all the invisible activity. At the same time, soap molecules combine to form a micelle, or cluster of soap molecules. These micelles distribute the fat in the milk.

This rapidly mixing fat and soap causes swirling and churning where a micelle meets a fat droplet. When there are micelles and fat droplets everywhere the motion stops, but not until after you've enjoyed the show!

There's another reason the colours explode the way they do. Since milk is mostly water, it has surface tension like water. The drops of food colouring floating on the surface tend to stay put. Liquid soap wrecks the surface tension by breaking the cohesive bonds between water molecules and allowing the colours to zing throughout the milk. What a party!
Additional Info
Repeat the experiment using water in place of milk. Will you get the same eruption of colour? Why or why not? What kind of milk produces the best swirling of colour: skim, whole milk, cream, milk powder?

Detergent, because of its bipolar characteristics (hydrophilic on one end and hydrophobic on the other), weakens the milk's bonds by attaching to its fat molecules. The detergent's hydrophilic end dissolves in water and its water-fearing end attaches to a fat globule in the milk.

I WONDER

• what would happen if I used a paper cup?
• if I used the paper cup muffins are baked in?