Slime Shop: Engineer Your Own Slime

Background Information for Teachers

"Slime" refers to a range of substances that you can buy or make yourself, like Gak™ or Silly Putty®. While their individual properties might vary slightly, in general, these substances are stretchy, gooey, sticky, or rubbery. Sometimes they might seem to behave like a solid; other times they might seem to behave more like a liquid.

Many slime recipes use glue and borax as the main ingredients. Glue is made of long, chain-shaped molecules called polymers. These molecules can easily slide over and around each other, kind of like the pasta in a pot of fresh-cooked spaghetti. This makes the glue very runny, which is why you can easily squeeze it out of a bottle. When mixed with borax*, the borate ions from the borax form weak bonds between the polymer chains in a process called crosslinking (Figure 1). This makes it more difficult for the polymer chains to slide around, making the glue less runny and more rubbery, forming slime. This reaction** results in an observable change in properties, as two different substances are combined to make a new substance with different properties. You can also add other ingredients to your slime to give it additional properties. For example, you can use iron filings to make magnetic slime.

Image Credit: Ben Finio, Science Buddies / Science Buddies
Figure 1. Straight polymer chains (left) are linked together by borate to form a cross-linked polymer (right).

Given the range of available recipes and ingredients for slime, your students have a lot of choices if they want to make their own slime. In this project, they will think like chemical engineers and design their own slime. First, they will need to decide what properties they want their slime to have. What color should it be? Should it be runnier or thicker? Fluffy? Magnetic? Glow in the dark? Then, they will need to do some background research and experiment to find out what recipe gives them their desired properties.

* In this lesson plan, we recommend that you use contact lens solution to make slime. It contains other ingredients (boric acid and sodium borate) that cause a similar chemical reaction, but it is safer to handle than borax, which can cause skin irritation with excessive use.

** At this level, we do not make the distinction between chemical and physical reactions. It is not always possible to determine which is which using easily observable properties like color or texture changes.

Additional Background Links

• The Engineering Design Process, Science Buddies

Prep Work (15 minutes)

Make one batch of slime that you can show your students at the beginning of the lesson.

1. In a mixing bowl, thoroughly mix 1/2 C water, 1/2 C glue, and a few drops of food coloring.
2. Add 1/2 tsp baking soda and mix completely.
3. Add 2 tbsp contact lens solution and stir vigorously until the mixture starts pulling away from the edges of the bowl.
4. Use your hands to knead the slime for 5-10 minutes until its texture stops changing. Do not worry if the slime is very runny and sticks to your hands at first. It will continue to get thicker as you knead it. This is important to remember for student clean-up! It gets easier to clean up the slime as you knead it more!

Engage (15 minutes)

Show the students the slime you made. Break it into smaller pieces and pass it around the classroom, so each student gets a chance to play with some.

How would you describe the slime? What properties does it have?

Students might describe how the slime appears (its color, whether it is shiny, etc.), how it feels (stretchy, rubbery, etc.), or even how it sounds. Encourage students to use all their senses except taste. It is not safe to eat the slime.

Now show the class the ingredients you used to make the slime (water, glue, food coloring, baking soda, and contact lens solution).

What are some properties of the individual ingredients? Are they the same or different from the slime?

Students might point out that some properties of the ingredients are different from the slime. For example, water is a clear liquid, and baking soda is a solid white powder. Other properties might match. For example, the slime should be the same color as the food coloring, but it is probably not as dark.

Why are the slime's properties different from the individual ingredients?

Let some students try to answer the question. Explain that sometimes when different materials are combined, it results in totally new materials with different properties, which is what happens when you make slime.

In this lesson, students will work in groups to design their own slime recipe. Explain that the slime you showed them is just one recipe. The amounts of ingredients in that recipe can be changed, and different ingredients can be added, resulting in slime with different properties. They will decide what properties they want their slime to have and then experiment to find the best recipe.

Explore (90 minutes)

1. Show the class the video on how to make slime.
   

   https://www.youtube.com/watch?v=bcfzUOdM8lg
2. Walk the entire class through making the base slime recipe. This will allow students to get familiar with making slime and start thinking about how they could change the recipe. It will also help you identify any problems or students who need extra help. Note that it will be easier if you do not make your own slime this time, so you are not caught with slime all over your hands if a student needs help. As students follow the recipe, encourage them to observe the properties of the individual ingredients and mixture. Do any of the properties change quickly or instantaneously? Do any of them change slowly?
   1. In a mixing bowl, thoroughly mix 1/2 C water, 1/2 C glue, and a few drops of food coloring.
   2. Add 1/2 tsp baking soda and mix completely.
   3. Add 2 tbsp contact lens solution and stir vigorously until the mixture starts pulling away from the edges of the bowl.
   4. Use your hands to knead the slime for 5–10 minutes until its texture stops changing. Do not worry if the slime is very runny and sticks to your hands at first. It will continue to get thicker as you knead it. This is important to remember for student clean-up! It gets easier to clean up the slime as you knead it more!
3. As a class, make a list of different properties and ways you could categorize or describe the slime. Here are a few ideas (your students may have more):
   • Appearance (could include color, shiny vs. dull, etc.)
   • Texture (sticky, smooth, rough, etc.)
   • Thickness (runny or liquid-like vs. thick and rubbery)
   • Weight or density (heavy vs. light and fluffy)
   • Bounciness
   • Stretchiness/squishiness
   • Additional "special" properties you saw in the video (glow in the dark, magnetic, etc.)
4. Optional: if your students have internet access, let them search online for other types of slime. There are many different slime recipes beyond those shown in the Science Buddies video. For example, try searching for "galaxy slime" or "fluffy slime." If they think of additional properties or categories, add them to the list.
5. Now, each group should use the student worksheet and make a list of properties they want their slime to have. This list should be based on the categories the entire class came up with, but they can add or remove things they deem important.
6. Make a list of ingredients that students will have available to them. Now, each group should look at their desired slime properties and the list of available ingredients. If an ingredient they need is not available, they may need to change their goal (for example, they cannot make magnetic slime if you do not have iron filings).
7. Each group should write down a recipe for their slime. This can be based on the starter recipe you did as a class or another recipe they found online. Their recipe should include any changes or additional ingredients they want to include in order to create slime with their desired properties.
8. Each group should follow the recipe they wrote down to make their first batch of slime.

   What is the slime like when you are finished making it? Does it have the properties you wanted?

9. Now each group should experiment with their recipe to see if they can improve the properties of the slime. First, they should think about what property they want to change and what ingredient would affect that property. Explain that it is important to only change one ingredient at a time, and not to change it dramatically (e.g., don't switch from using 2 tbsp of contact lens solution to 2 cups). For example:
   • Slime's color was too light → add more food coloring
   • Slime was too runny → add more contact lens solution
   • Slime was too fluffy → use less shaving cream

   Have students make another batch of slime with the modified recipe. Each group should now have three batches of slime: the "standard" batch they made as a class, their original custom recipe, and their second custom recipe. They should compare the properties of each batch of slime to their desired properties and choose the best one to show the rest of the class.

Reflect (15 minutes)

Arrange a "slime show and tell" for the entire class. One or two students from each group should remain at their table to show off their slime while the other students get up and walk around the class to see everyone else's slime (rotate roles so everyone gets a chance to walk around).

As a class, discuss the different types of slime the students came up with. Did any groups have very similar slime? Did any groups have a unique type of slime that no one else made? How do the properties of the different types of slime compare?

Optionally, you can let the class vote to decide on their favorite slime or give each group a "budget" (e.g. a certain amount of money or coupons) they can use to "purchase" slime from other groups. Who sells the most slime? Why do students like some types of slime better than others?

Clean-up

All ingredients and slime can be safely disposed of in the trash or stored in airtight containers for future use.

Assess

Each student's worksheet can be used to assess their performance during the lesson.

Optional: ask each group to give a brief presentation to the class that includes:

• The desired properties for their slime and why they chose them
• The testing process they used (e.g., what ingredients did they decide to change and why)
• Their results (which batch of slime did they decide was best and why)

Make Career Connections

Discussing or reading about these careers can help students make important connections between the in-class lesson and STEM job opportunities in the real world.

Chemical Engineer

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Career Profile

Chemical engineers design many of the products we use every day, like soap and shampoo. They might experiment to find the best recipe for something or the best way to mass-produce it in a factory. If you enjoyed experimenting with different ways to make slime, you might want to learn more about chemical engineering! Read more

Materials Scientist and Engineer

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Career Profile

Materials scientists figure out how to create new materials, or modify existing ones, to get desired properties. For example, they might figure out how to make stronger metals so engineers can build a stronger bridge, or they might develop totally new bio-compatible materials that can be used in artificial organs or prosthetic limbs. If you had fun choosing and analyzing the properties of your slime, you should read more about materials science! Read more

Lesson Plan Variations

• Have your students use a scale to weigh all of the individual ingredients before mixing and weigh the slime after finishing the recipe. This should show that the total amount of weight did not change, even if some ingredients (like the baking soda) seem to "disappear" (NGSS 5-PS1-2. Measure and graph quantities to provide evidence that regardless of the type of change that occurs when heating, cooling, or mixing substances, the total weight of matter is conserved).