WHAT IS POLARITY?
Polarity is a chemical property of a molecule that describes a distribution of the electrical charge inside of it.
A molecule is polar when there is a difference between electronegativity of its atoms and nonpolar otherwise. Electronegativity describes how easy is for an atom to receive electrons.
You probably noticed that some liquids mix together well and some don’t. For example, water and sugar mix while water and oil keep separated. Why is that?
Molecules of the different polarity don’t mix together, in this case, both sugar and water are polar molecules and the oil is nonpolar.
If you want to know more details about polarity, please read our Lava lamp experiment article, where we discuss this topic in more detail.
SCIENCE BEHIND THE COLORFUL MILK POLARITY EXPERIMENT
Milk contains few different ingredients, mostly water, but also some mineral, proteins and fat. And we already learned water is polar molecule while all fats are nonpolar.
But what about the dish soap? Soap is used primarily for washing different types of grease and dirt, stuff that water can’t dissolve by itself. And to be able to do that effectively it must be able to mix with nonpolar molecules. On the other hand, we know that we can mix soap with water and get a bubbly solution. How is that?
Well, soap molecule is made out of the long nonpolar tail and short polar head, so it can mix with both types of molecules!
When we put it into the milk, the nonpolar tail will collect fat molecules, while the head will mingle with the water molecules.
In all that movement, the food colors are pushed around and we can observe a real visual spectacle.
MATERIALS NEEDED FOR THE COLORFUL MILK POLARITY EXPERIMENT:
- Milk
- Plate
- Food colors
- Dishwashing soap
- Cotton swab
INSTRUCTIONS ON DOING THE COLORFUL MILK POLARITY EXPERIMENT:
Watch the video at the beginning of the article for step by step instructions or continue reading.
- Pour the milk into the plate (milk with more fat content is better).
- Put few drops of food coloring in the middle (if the color is too thick, dilute it with few drops of water)
- Soak the cotton swab into the dishwashing soap
- Touch the colors with it and observe what happens!
WHAT WILL YOU DEVELOP AND LEARN:
- Chemistry knowledge
- Concept of polarity
- What is soap and how does it work
- Mixing colors
- How to conduct an experiment
If you liked this experiment and would like to try even more fun chemistry experiments, we recommend How to make plastic with milk and vinegar and How to make sugar crystals.
