Science Smarts: A little something to wow students as they return to classrooms

By Patty Rooks on September 7, 2024.

I survived the first week back to school! It is hard to get back in the routine, even after all these years but I think we have it down once again. What a busy time, but one of my favourites as it is wonderful to see all those young smiling faces crowding the hallways of our schools. I know it has been a busy week of learning, but here is another activity sure to wow the students in the classroom as we all get settled in. Let’s get started!

*Remember to ask an adult before doing this experiment.

Materials

– Milk (whole)

– Dinner plate or Pie Plate

– Food colouring (red, yellow, green, blue – primary colours)

– Dish-washing soap (Dawnâ„¢ brand works well)

– Cotton swabs

Procedure

1. Pour enough milk in the dinner plate to completely cover the bottom. Allow the milk to sit for a couple of minutes and 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 swab 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 swab. Go ahead and try it.

4. Now place a drop of liquid dish soap on the other end of the cotton swab. Place the soapy end of the cotton swab 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 of the cotton swab and try it again. Experiment with placing the cotton swab at different places in the milk. Notice that the colours in the milk continue to move even when the cotton swab is removed. What makes the food colouring in the milk move?

Extension

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, 1%, 2%, or whole milk? Why?

What is going on?

It’s an explosion of colour! Some very unusual things happen when you mix a little milk, food colouring, and a drop of liquid soap. Use this experiment to amaze your friends and uncover the scientific secrets of soap.

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 becomes a free-for-all! The molecules of protein and fat bend, roll, twist, and contort in all directions. The food colouring 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 the micelles and fat droplets have dispersed throughout the milk 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.

Mark your calendars, the Praxis AGM is fast approaching on Wednesday, September 11, 2024. We are always looking for volunteer Board members, so please consider joining us. If interested, please reach out to Patty for further details.

Patty Rooks, senior scientific consultant PRAXIS, “Connecting Science To The Community.” Contact Praxis at praxis@praxismh.ca, http://www.praxismh.ca, Tweet or follow us @PraxisMedHat, or friend us on Facebook. Address: 12 826 11th Street SE, Medicine Hat, AB, T1A 1T7 Phone: 403-527-5365, email: praxis@praxismh.ca.

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