Home School - Breaking Down Fat

One aspect of Home Education that I love is the free learning that can come from everyday life.

Recently, the boys and I were cleaning and I was doing the washing up. Whilst doing it William asked with I had to use the washing up liquid and didn’t just rinse the plate under warm water and scrubbed as hard as I could.

For a moment I had to think. I knew the science behind it; Washing up liquid contains detergent molecules. These molecules have a very specific structure with a polar head group and a long hydrophobic (water-hating) tail. When you dissolve the detergent in water, it assembles automatically to form a “supermolecule”. The hydrophobic tails interact with one another and want to hide from the polar water molecules. The charged head group, in contrast, wants to interact with the polar water molecules.

However, I realised that this would totally confuse the boys and wouldn’t explain what happens.

Instead I explained that the liquid helps separate the fat and oil from the water. Once done it bonds between the two; one creating a “fat and oil” layer and the other water.

Although the boys understood this I felt that we needed to cover it within a science lesson!

With that in mind I remember a simple but effective science experiment!

Resources

Baking Tray

Foil

Full Fat Milk

3 Different types of Food Colouring

Washing up Liquid

Method

We started by lining the baking tin with foil. We did this so we could it was a clean and pure experiment against a neutral and non-contaminated surface.

We then poured the full fat milk into the tray. Ideally the experiment only works with full fat milk as we are aiming to see a difference within the two liquids. That said, it may be possible with semi-skimmed milk and certain types of food colouring. (However, we wanted to see clearer and better results)

We then poured the different colours into the tray. We limited it to a few drops per colour. What you then see is the colouring sitting on top of the milk. The fat within the milk holds a stronger bond together and the liquids hold above it.

We then added the washing up liquid but only a few drops of it.

What you will see in the above picture is the bursts of colours expanding out once the liquid was added.

With more washing up liquid added you can see that the colours now swirl around and move to a marble effect. The dish soap does not mix with the milk. Instead it floats on top and spreads over the surface. As it spreads, it grabs the food colouring. Soap is a "degreaser" so the molecules in it are attacking the fat in the milk, causing motion which creates the swirling of the colours. Where the colours meet, they combine and form new colours.

We then went off to discuss that liquids like water and milk have a property known as surface tension, due to the cohesive forces of the liquid's molecules. If you look closely at the edge of the surface it appears to rise up the side of the glass because the surface tension of the water is actually pulling the water away from the glass inward toward the centre of the surface. Since milk is mostly water, it has surface tension like water. Homogenized milk has gone through a process where the fat is broken up into tiny pieces of fat called globules and spread throughout the milk. When the food colouring was added to the milk, the fat globules were steady and undisturbed. Food colouring is less dense than milk, so it floats on the surface. When dish soap touches the surface of the milk, things begin to move. Dish detergent weakens the milk's bonds by attaching to its fat molecules. As the dish soap diffuses into the solution it surrounds the fat globules in the milk.

We loved doing this and it was a clear and visual experiment that showed what happens when fat is broken down with the use of washing up liquid..

What do you think? Would you try this?