Do you ever think about milk as it slips and sloshes into your cereal bowl? This white liquid's yummy with breakfast and cookies, but there's a lot more to milk than its tastiness. Milk is mainly made of water; the other big ingredient is usually fat. If it wasn't for the fat in milk, our breakfast cereal would taste like it was soaking in water. Delicious? Probably not.
Not all milk has the same amount of fat. But how can we tell the difference? With this color changing milk experiment, we'll be using dish soap to look at different amounts of fat in milk.
How will different types of milk react to dish soap?
- 4 bowls
- 1 cup whole milk
- 1 cup 2 percent milk
- 1 cup 1 percent milk
- 1 cup skim milk
- Sticky labels
- Food coloring
- Dish soap
- Using your pencil, write each of your different types of milk on a sticky label: Whole, 2 percent, 1 percent and Skim.
- Place one sticky label on each of your bowls.
- Fill each bowl with the type of milk written on its label. If you accidentally put the wrong type of milk into the wrong bowl—for example, skim milk in the bowl labeled Whole—don't worry; you can always pour it in the sink and start again.
- Think about what you already know about this creamy white drink. Whole milk contains a lot of fat, but skim milk is completely fat-free. Do you think dish soap will act the same when added to these different types of milk? Write down any notes in your notebook.
- Using your notes from step 4, make guesses about what will happen when you mix the different types of milk with dish soap and food coloring. Include separate guesses—called hypotheses—for each of your four different types of milk.
- Squeeze a few drops of food coloring into the bowl of whole milk. Wait for 30 seconds.
- Drip two drops of dish soap into the center of the bowl. What happens? Does the food coloring move?
- Turn to the next page of your notebook and write "Whole Milk" at the top.
- Write down what happened to the food coloring in the whole milk bowl.
- Repeat steps 6-9 with the three other types of milk.
The food coloring in the whole milk bowl should appear to dance and move around as soon as the dish soap is added. The same thing will happen in the bowl of 2 percent milk, although the food coloring won't move around as much. The food coloring will dance even slower in the bowl of 1 percent milk and hardly at all in the bowl of skim milk.
The food coloring in the whole milk bowl will move the fastest because the dish soap bonds, or holds tight, with the fat in the milk. This bond is so strong that the water and the food coloring are pushed out. Everything else has to dance out of the way to make room for the dish soap and fat bond. Since there is less fat in 2 percent and 1 percent milk, you won't see as much movement. In the bowl of skim milk, the dish soap has no fat to bond with, so the food coloring isn't pushed away.
Don't let the color changing milk experiment end here! Try out different types of milk and guess what will happen when you add dish soap. You can use soy milk, coconut milk, almond milk, or goat milk. What about half-and-half, condensed milk, chocolate milk or heavy cream?
Once you are done testing milk products, see if the experiment will have the same affect on other liquids. Some liquids you can test include water, apple juice, chicken broth, coffee and ginger ale. Add your observations to your notebook. Compare your results with the results you got from testing the different types of milk.