11 Lessons to Teach About the Chemistry of Mixtures and Solutions
Use these free STEM lessons and activities to help students get hands-on experimenting with the science and chemistry of mixtures and solutions.
Most students have a basic concept of "mixtures." They have combined ingredients in the kitchen. They know that beverages, paints, and glues are mixtures. They may realize that blood is a mixture, as is the air we breathe. They know that some things "mix" well and others don't and that some mixtures are permanent and others separate or dissolve after time. Combining substances and exploring the chemistry behind what happens and why is science that is observable and actionable.
When substances are combined, they may form a mixture, in which the individual substances retain their chemical properties, or they may form a chemical reaction, in which a new substance with its own chemical properties is created. The free STEM lessons and activities below all involve mixtures, combinations that do not result in a chemical change. In these lessons and experiments, students learn about heterogeneous and homogeneous mixtures and explore solutions, colloids, suspensions, emulsions, and more. As they investigate the chemistry of mixtures, they learn about hydrophobic, hydrophilic, and immiscible properties; solvents and solutes; solubility and saturation; phases; the Tyndall effect; and how mixtures are related to real-world challenges and solutions. (Note: In some of these resources, other science topics are also being taught or highlighted by the hands-on activity, but each lesson demonstrates the chemistry of certain types of mixtures as well.)
The resources below have been grouped as follows:
Note: Science Buddies Lesson Plans contain materials to support educators leading hands-on STEM learning with students. Lesson Plans offer NGSS alignment, contain background materials to boost teacher confidence, even in areas that may be new to them, and include supplemental resources like worksheets, videos, discussion questions, and assessment materials. Activities are simplified explorations that can be used in the classroom or in informal learning environments.
Lesson Plans and Activities to Teach About the Chemistry of Mixtures and Solutions
A homogeneous mixture is one in which the composition of the mixture is uniform throughout. Solutions and alloys are types of homogeneous mixtures.
You can make a simple bubble solution for blowing bubbles by combining liquid dishwashing soap and water, but chemistry holds the secrets to making better bubble solutions that create larger or longer-lasting bubbles. In the Blowing the Best Bubbles activity, students investigate the formula for bubble solution. When added to water, the liquid dishwashing soap reduces the surface tension of the solution, which makes it possible to form bubbles. Once combined, the mixture is a homogeneous solution. When left standing, the ingredients don't separate. Questions: What happens when corn syrup or glycerin is added to the bubble solution? What causes a bubble to pop?
When you dissolve a soluble substance in a liquid, you make a solution. Mixing a lemonade powder (a solute) with water (a solvent), for example, creates a solution. The resulting lemonade is a homogeneous solution because, once stirred in, the substances are uniformly combined and should not separate when the lemonade is left standing. You don't have to stir your lemonade again to remix the ingredients before taking another drink later! In the Solubility Science: How Much is Too Much? activity, students explore solubility and experiment to find out if there is a limit to how much solute can be added to the solvent when making a solution. Questions: If you see a substance floating or collecting at the bottom of a container of a mixture that should form a solution (rather than a suspension), what has happened? If you make a mixture with an insoluble substance, what happens? What does it mean for a solution to be saturated?
Making a slushy involves turning flavored water or fruit juice into an icy, drinkable treat. In the Homemade Slushies activity, students make slushies and explore the science behind how using a salt-water solution helps the slushy mixture form ice crystals. The salt-water solution used to cool the slushy is a homogeneous solution. Questions: What role does the salt-water solution play in making a slushy? If you use sugar and water for the slushy mixture, what kind of mixture have you created? If you use a fruit juice with pulp combined with another liquid, what type of mixture is created?
Making rock candy involves growing crystals from a saturated solution of sugar and water, one that has more sugar than can dissolve in the water. In the Grow Rock Candy Crystals activity, students explore the science behind the crystallization process and how a saturated solution helps enable crystal formation. Questions: What is nucleation in the crystallization process? How do seed crystals help speed up crystallization? Can crystallization happen if the sugar-water solution is not saturated?
What happens to the substances in a solution when you heat the solution to boiling? In the Separation By Distillation activity, students investigate by building a distillation device and boiling fruit juice. A homogeneous solution can't be filtered to separate it into its original separate substances, but the distillation process does this using heat. In distillation, a mixture can be separated by a thermal process because of the differences in the boiling points of the substances in the homogeneous mixture. Questions: What does the steam released as the fruit juice boils contain? What kinds of real-world solutions might use the distillation process?
A heterogeneous mixture is one in which the composition of the mixture is not uniform all the way through. Suspensions, colloids, and emulsions are types of heterogeneous mixtures. When investigating these types of mixtures, students learn how to differentiate between a suspension and a colloid and what makes a colloid different from an emulsion.
If you open a box of cereal that contains dried fruit, you will probably find that the fruit isn't evenly distributed. Even if you shake the box, there will be more fruit in some areas than others. You might see this in a container of trail mix or mixed nuts, too. If the container is clear, you will be able to observe how the different ingredients are distributed. When you shake a container of granular items, the distribution may change, but it still won't be even. Ultimately, each handful, cup, or scoop removed from one of these mixtures will have a different distribution of ingredients. If you are hoping for more candy bits than nuts in your serving of trail mix, you may have to go digging! These are examples of heterogeneous mixtures. In the Why Won't it Mix? Discover the Brazil Nut Effect activity, students use candy sprinkles and sand to explore the science behind the distribution of granular substances in mixtures and experiment to see what determines how the ingredients separate. Questions: How does the size or mass of the substance or ingredient affect what happens to it in a granular mixture? What examples can you think of where this kind of mixing would be an advantage?
No one wants to drink water that has dirt and debris floating in it! Surface waters often contain visible particles that make it look cloudy. These solid particles floating in the water are "suspended" in the water and are called total suspended solids (TSS). TSS don't dissolve. If large enough, they should settle to the bottom, but many TSS are small and light. TSS can carry bacteria, so water containing TSS isn't safe to drink. In the Drinking Water Cleanup activity, students learn how coagulation and flocculation are used to help separate TSS from water in a water processing plant. Coagulants and flocculants help smaller particles clump together so they are heavier and settle to the bottom more quickly. In the activity, students simulate water treatment by using alum as a coagulant to clear a sample of turbid water. (For a related student science fair project, see From Turbid to Clear: How Flocculation Cleans Up Drinking Water.) Questions: Why do coagulants need to be stirred to be effective? What does the charge of TSS particles have to do with how coagulants work?
Oobleck is well-known for its non-Newtonian properties. Sometimes it behaves like a liquid (fluid), and sometimes (when under pressure) it acts like a solid. In the Oobleck: A Recipe for a Mesmerizing Mixture activity, students make Oobleck and explore its behavior. As a mixture, Oobleck is a heterogeneous mixture of water and cornstarch. When you mix a solid and a liquid together, the solid usually either dissolves or separates from the liquid. In a suspension or colloidal solution, however, particles of the solid are suspended in the liquid. In Oobleck, cornstarch is evenly spread throughout the water, but it doesn't dissolve in the water. Depending on the size of the cornstarch particles, they may be too small to see with the naked eye, so it may look like they dissolved in the water, but they are actually suspended in the liquid. These particles would scatter a beam of light, which is referred to as the Tyndall effect. A suspension with very small particles (smaller than 1μm) is called a colloid. Questions: Can the particles in a colloid be separated from the mixture? If your Oobleck separates after sitting, what does that tell you about the particles? If the cornstarch dissolved in the water, what would the mixture be called? How does the fact that cornstarch molecules are hydrophobic help explain what happens when cornstarch is mixed with water? What is the difference between a suspension and a colloid?
Ferrofluids, fluids whose shape can be changed by magnetic fields, are made by combining ferromagnetic materials (like iron or nickel) with a surfactant and a carrier fluid. When combined, the ferromagnetic particles are suspended in the solution rather than dissolved. In the Magnetic Fluids lesson, students learn about ferrofluids and then make and write with magnetic ink. Depending on the size of the ferromagnetic particles, the ink mixture might be a suspension or a colloid. Questions: How can you tell if the magnetic ink is a suspension or a colloid? What difference will the size of the particles make in how the ink is used or readied for use?
10. Making Butter
Butter is basically milk fat that is separated out when cream is shaken (or agitated). In the Scrumptious Science: Shaking for Butter activity, students shake heavy whipping cream to make their own butter emulsion. An emulsion is a special type of colloid in which one liquid is suspended in another. The liquids in an emulsion are ones that usually do not mix well. In the case of butter, small droplets of water are suspended in the fat from the cream. (The liquid that remains is buttermilk.) The high concentration of fat makes the butter feel solid. If you melt it, the emulsion breaks.Questions: What role does temperature play in making butter? What does shaking do in this process?
11. Making Ice Cream
When kids make ice cream in a bag, they learn about the role of salt in lowering the freezing point. The recipe for making ice cream involves a mixture of ingredients. When using sugar and milk (or cream), the resulting emulsion looks homogeneous, but if you were to zoom in, you would see a heterogeneous mix of milk-fat, ice crystals, and sugar-water. Adding other ingredients, like chocolate chips, makes the mixture even more heterogeneous. Make Ice Cream in a Bag activity, students make ice cream in a bag. Questions: What role does salt play in speeding up the freezing process? Why is it necessary to shake the bags to make the ice cream form? What is a freezing point depression?
The following word bank contains words that may be covered when teaching about the chemistry of mixtures using the lessons and activities in this resource.
- Brazil nut effect
- Distill (distillation)
- Heterogeneous solution
- Homogeneous solution
- Immiscible (immiscibility)
- Saturation (saturated)
- Soluble (solubility)
- Total suspended solids (TSS)
- Tyndall effect
For more resources to teach K-12 chemistry, see the following resource collections:
- Teach Chemical Reactions - 20+ Chemistry Lessons and Activities
- Green Chemistry and the School Science Lab - Safer Chemistry for Today and Tomorrow
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Collections like this help educators find themed activities in a specific subject area or discover activities and lessons that meet a curriculum need. We hope these collections make it convenient for teachers to browse related lessons and activities. For other collections, see the Teaching Science Units and Thematic Collections lists. We encourage you to browse the complete STEM Activities for Kids and Lesson Plans areas, too. Filters are available to help you narrow your search.
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