Today you are going to see how a simple drop of dish soap can affect surface tension and the chemical bonds of fats and proteins in milk. Although milk is mostly made up of water, it also contains vitamins, minerals, fats, and proteins. These are evenly distributed as a solution and are held together by weak chemical bonds.
Before we move on, what is a chemical bond? A chemical bond occurs when two or more atoms are attracted together and combine to create a new chemical substance. Atoms may be attracted to one another for many different reasons, but nearly all bonds form because the final products are more stable than the original reactants. Some bonds are stronger than others. Weaker bonds are more easily broken. There are several types of chemical bonds, including ionic, covalent, and polar covalent bonds.
Here’s one example of a chemical bond (more specifically, a covalent chemical bond):
Learn more about bonds here:
Where else (besides in milk) might you find chemical bonds?
Because the chemical bonds in milk are relatively weak, the solution is easily altered. When you add a drop of dish soap, for example, the bonds are broken and the molecules of fat and protein move around and bump into each other.
What does dish soap have to do to with this? Think about trying to wash a greasy plate with no soap. The grease just resists the water, and you can never quite get it clean. If you add dish soap, no problem! The grease comes right off with the suds. Why is this? Dish soap links grease and water together! The polar (hydrophilic) end of dish soap molecules are attracted to water while the nonpolar (hydrophobic) ends bind to the grease. This brings the water and grease together and allows you to scrub the grease off.
In your activity, you will see how dish soap affects the bonds between fats and proteins in the milk!
- Hydrophobic (water fearing)
- Hydrophilic (water loving)
- Chemical bonds
Check out this video to see what you will be doing today!
YOU WILL NEED
- Food coloring
- Dish soap
- Cotton swabs
- Dinner Plate (make sure it’s deep enough to hold about 1/4 inch of liquid)
Here’s what to do!
- Carefully pour milk onto the dinner plate until it is about 1/4 inch deep.
- Add one drop of food coloring into the center of the milk on the plate. Be careful not to bump the plate!
- Select a second color and add one drop near the first drop.
- Repeat step 3 with two other colors.
- Select a cotton swab.
- PREDICT: What will happen when you touch the cotton swab to the center of the milk?
- Touch the cotton swab to the center of the milk and record what happens.
- Select a second cotton swab and squirt a small drop of liquid dish soap onto the end.
- PREDICT: Now that you have added liquid dish soap, what will happen when you touch the cotton swab to the center of the milk?
- Check it out! Touch the cotton swab with dish soap to the center of the milk and hold it there for 15 seconds. How was this different than the first time you touched the plain cotton swab to the milk? Record your observations!
- Select another cotton swab, add a drop of dish soap to the end, and try it again. What happens with you place the swab at different points in the milk?
What exactly did you observe? Why did the dish soap cause the colors in the milk to move?
How can you make this demonstration an experiment? Instead of just using one kind of milk, try out this activity with different kinds of milk. For example, you could use skim, 1%, and 2%. You could also choose milk alternatives such as almond milk or soy milk. Observe the differences and then compare and analyze your results!