The Soap Experiment

We know soap is used to wash the dirt off our hands and bodies. We also know soap is used to wash other things such as the dishes we eat off of, the clothes we wear, the dog (when he runs through the mud), and even your mom and dad’s car. But have you ever stopped to think about what soap is?

Soap is made from water, ashes, and fat from either animals or plants. When the three are mixed together a chemical reaction takes place. This means the water, ashes, and fat turn into something different. They turn into what we call soap.

When the chemical change takes place to make soap, two types of molecules are created. The two types of molecules in soap are hydrophobic and hydrophilic molecules.

The hydrophobic molecules grab hold of the dirt and oil on your hands or body. The hydrophilic molecules like to mix with water to make suds or lather. By working together, the two types of molecules remove the dirt from your body and take it away.
But guess what else happens? The chemical change is so powerful that when soap comes near more fat, the soap acts like a magnet and pulls the fat toward it.

Does this sound strange to you? Let’s see how it works…

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  • 1 plate or round cake pan
  • Milk (whole milk)
  • Liquid food coloring-2 or 3 different colors
  • Dish soap


  • Carefully pour just enough milk onto the plate or into the pan to cover the bottom (without letting it spill over the edges of the plate).
  • Drop 2 or three tiny drops of each color of food coloring into the milk. Do this slowly and carefully without disturbing the milk.
  • Carefully place 1 or 2 drops of dish soap into the center of the plate of milk.
  • Watch the colors mix, swirl, and run away.


Milk is made up of water, fat, protein, vitamins, and minerals. When the soap touches the milk, the fat is pulled away from the other things in the milk and pulled toward the soap like a magnet pulls metal.

When the fat begins to move toward the soap, it pushes everything else out of its way so it can join to the soap as quickly as possible.

You might wonder how the fat in milk can push everything else out of its way to get to the soap. Great question! The fat particles in milk are larger and lighter than the water, vitamins, and minerals in the milk. Their larger size lets them push their way through everything to get to the soap. Their lightweight lets them move faster than everything else in the milk.

The fat does not mind being pulled toward the soap because when fat is mixed with soap, the chemical change that wants to turn the fat into more soap just automatically happens. This process is called saponification (sa-pon-a-fi-k-shun).


  • Once the color swirls settle down, try adding a drop of dish soap somewhere else in the milk. Does anything happen or has all the fat in the milk gathered itself to the first drops of dish soap added to the milk?
  • Try the experiment again using a square or oblong pan. Did anything different happen?
  • Repeat the experiment with 2%, 1% and/or skim milk. Are the results the same as they were using whole milk? If not, why do you think the results were different?
  • Try the experiment using both cold and warm or hot milk. Are the results different? If so, why do you think the results were different?


  • Soap is made of water, ashes and fat.
  • Mixing water and ashes together makes lye.
  • Mixing lye with fat to make soap is a chemical reaction.
  • A chemical reaction is when substances change to make a new substance.
  • Both animal and plant fats can be used to make soap. Olive oil, coconut oil, soybean oil, and almond oil are some of the plant fats you can use to make soap.
  • Mixing fat with lye to make soap is called saponification.
  • The higher the fat content in the milk, the more the food coloring will mix and move.
  • The warmer the milk, the faster the fat particles move toward the soap.