Author: Maddie Van Beek
This week was Independence Day, and we're going to continue the fun with some 4th of July themed science activities! First, we will learn about surface tension and chemical bonds by making fireworks in milk! These fireworks don’t explode, but they do create awesome swirling colors! Let’s get started!
We are going to find out how a simple drop of dish soap can make big changes in milk.
First of all, what is milk made of? Make a list.
You may have listed vitamins, minerals, fats, and protein (all great nutrients for our bodies!) but milk is made up mostly of water. All the other stuff is evenly distributed as a solution held together by weak chemical bonds.
A chemical bond occurs when two or more atoms are attracted together and combine to create something new. 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. Can you think of anything else that might involve chemical bonds? Make a list!
Even the simplest things can be created with chemical bonds, such as water and air! Water is hydrogen bonded with oxygen (H2O), while air is two oxygen molecules bonded together (O2).
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. Once broken, the molecules of fat and protein move around and bump into each other.
Why does dish soap cause 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 hydrophilic (water loving) end of dish soap molecules are attracted to water while the hydrophobic (water fearing) ends bind to the grease. This brings the water and grease together, which allows you to scrub the grease off.
Let’s see this in action!
YOU WILL NEED
* Whole Milk
* 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!
1. Carefully pour milk onto the dinner plate until it is about 1/4 inch deep.
3. Add one drop of blue food coloring near the first drop.
4. Continue to carefully add a few other drops.
6. PREDICT: What will happen when you touch the cotton swab to the center of the milk?
7. Touch the cotton swab to the center of the milk and record what happens.
8. Select a second cotton swab and squirt a small drop of liquid dish soap onto the end.
9. PREDICT: Now that you have added liquid dish soap, what will happen?
10. 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!
11. Select another cotton swab, add a drop of dish soap to the end, and try it again. What happens when 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! You could also try different kinds of soap or sanitizer. Is one more effective than another?
Red, White, and Blue Density Tower
Next, you will be experimenting with liquid density. When you dump more than one liquid together, what do you think happens? If the densities are the same, they will just mix. For example, yellow Gatorade and blue Gatorade would make green. But if the densities are different, you can actually layer liquids to make stripes in a jar! Before we try layering any liquids, you need to know a little bit about density.
Density is the amount of matter in a given space. The density of any given liquid (or solid or gas) is determined by how closely the molecules in that liquid are packed together.
Think about it. Let’s say you put five gummy bears into a Ziploc bag for your little brother and 20 gummy bears into the same size Ziploc bag for yourself. Whose bag of gummy bears is more dense?
A liquid with fewer molecules per unit of volume is less dense than a liquid that has more molecules per unit of volume.
Which figure is more dense?
Demonstration: Pour 1/4 cup oil and 1/4 cup water into a glass. Which liquid sinks to the bottom (aka, which liquid is more dense?)
What does this tell you about these two liquids?
So you know that water is more dense than oil. Now, let’s try this out with a bunch of
liquids. By using many liquids of varying densities, you can make liquid stripes in a jar!
YOU WILL NEED:
* Jar or clear glass
* Food coloring
* Olive oil
* Corn Syrup
* Dish soap
Here’s what to do!
1. The first liquid that you will add to your jar is the corn syrup. Make sure you pour it straight into the middle of the jar--be careful not to get it on the sides!
* How were you able to layer liquids?
* Explain why these liquids didn’t just mix together.
* Were you surprised by your results? Why or why not?
* Draw your density tower and label each layer to record which liquids are more or less dense.
Extension: Try this out with different liquids! See if you can discover densities of other common liquids in your home.