Properties of Mixtures vs. Solutions: Mix It Up! - Lesson (2024)

Introduction/Motivation

What is the difference between a solution and a mixture? Well, have you ever made chocolate milk? Have you ever noticed what happens if you let your chocolate milk sit for a while? Well, sometimes the chocolate will settle on the bottom of the glass. This is because it is a mixture. Mixtures are any combination of two or more items. Sometimes the two or more ingredients look all the same when mixed together and sometimes they do not.

Have you ever made a drink with water and a powder? How about lemonade from a mix? This is an example of a solution. What does the powdered drink look like after you stir it in water? Is it all the same color and consistency? It probably is, and that is one characteristic of a solution — that it is hom*ogeneous (or that it is uniform throughout). What other solutions have you made? (Solicit answers like: salt water, mud pies, bubbles, etc.) Solutions are types of mixtures, but mixtures can also be heterogeneous, where you can see the different ingredients separated out. Refer to the associated activity Messin' with Mixtures for students to further their understanding by investigating a heterogeneous mixture as environmental engineers analyzing a soil sample, using trail mix.

Teacher demonstration: Set up three glasses of water.

1. Add pebbles of sand to the first glass. Stir the water. Ask students whether this is a mixture or a solution. (Answer: It is a mixture because the sand and the water stay separate. The sand does not disappear in the water.)
2. Add a teaspoon of salt to the second glass. Stir the water until the salt disappears. Ask students if this is a mixture or a solution. (Answer: It is a solution because the salt dissolves, or disappears, in the liquid.)
3. Ask students if two liquids will form a mixture or a solution. Then add some vegetable oil to the third glass and stir. Ask students if the glass contains a mixture or a solution. (Answer: The oil and water form a mixture because they do not mix. The oil does not disappear or dissolve.)

Can you separate mixtures and solutions back into their original components? Yes you can! Sometimes you can separate out the parts of a mixture using something as easy as a filter or screen. You cannot use a filter or a screen to separate out the parts of a solution. Therefore, another way to separate mixtures and solutions is to use the three phases of matter: solids, liquids and gases. Who remembers what the solid phase of water is? (Answer: ice) How about the liquid phase? (Answer: water) The gas phase? (Answer: steam) As you heat up a solid, it will eventually turn into a liquid, and then into a gas. Most solids at room temperature (25oC) need an incredible amount of heat and pressure in order to liquefy (turn into a liquid from a solid). Which of these three phases is air in? (Answer: gas) What about orange juice? (Answer: liquid) How about the table and chairs in this room? (Answer: solid) We can often separate the parts of a mixture or solution by trying to change the phase of matter that the mixture or solution is in.

A solution is made of a solute and a solvent. What does that mean? Well, a solute is something that dissolves in a liquid and a solvent is the liquid that something dissolves in. The solute dissolves in the solvent. In a saltwater solution, the salt is the solute and the water is the solvent. Can we separate the salt and water from the saltwater solution? (Yes, the salt can be retrieved by evaporating (heating) the water from a liquid to a gas, leaving only the salt behind.)

How do we use mixtures and solutions in our daily lives? Well, we have named a few examples of mixtures and solutions we have in our homes already. How do engineers use mixtures and solutions? Well, engineers use mixtures and solutions in many different applications. Think about the demonstration with the three glasses of water. Environmental engineers use mixtures to learn how to separate oil from water in oil spills. Also the process of making gasoline from crude oil involves separation steps that are based on the properties of mixtures and solutions. Water resource engineers study mixtures and solutions in order to get sand, salt and chemicals out of water so it can be used for drinking and cleaning. Biomedical engineers even use mixtures and solutions to develop new medicines.

Lesson Background and Concepts for Teachers

Mixtures vs. Solutions

When two or more kinds of matter are put together it is called a mixture. Mixtures can be made with solids, liquids or gases. Any combination will result in a mixture. Once made, mixtures can be separated using mechanical, screening or filtering processes. The components of a mixture are not changed when mixed with other materials. However, sometimes when two or more materials are mixed, a special kind of mixture is formed. For example, when you mix salt and water, the solid (salt) seems to disappear in the water. This process is called dissolving, and will form a solution. When a solid is dissolved in a liquid, we call the liquid a solvent and the solid is called the solute.

Like a mixture, solutions can be separated into its original components. However, unlike mixtures, solutions can be separated by evaporation. For example: the water and salt solution will evaporate as the solution is heated. The water will change from liquid to gas as the water-salt solution begins to boil, leaving only the salt behind. Most solutions are made by mixing a solid and a liquid. Mixing matter in other states can also make solutions. For example, air is a solution resulting from the mixing of several gases.

Associated Activities

• Messin' with Mixtures - Students investigate a heterogeneous mixture as environmental engineers analyzing a soil sample, using trail mix.

  Watch this activity on YouTube

Lesson Closure

Who can tell us one difference between a mixture and a solution? Well, a mixture is made up of two or more kinds of matter but sometimes you can still see the different components, like sand and water. In a mixture, all the different parts retain their original properties. A solution is a special type of mixture that is hom*ogeneous, where you cannot tell the difference between the components. A solution is also a special type of mixture that cannot be separated via mechanical means – filtering, screening, etc. In most cases, a solution has different properties than the two or more parts that went into making it.

Can you separate out the parts of a mixture or solution? Yes, you can! Often, you can separate a mixture by using a filter or screen. You can also try and change the phase of matter that the mixture or solution is in. Who can name the three phases of matter that we are referring to? (Answer: solid, liquid and gas.) An example of separating a solution using the phases of matter is evaporating the water from a saltwater solution. This is where we heat the liquid water into a gas, leaving only the salt behind.

Engineers are always designing and experimenting with new ways of separating mixtures and solutions based on their properties. They are also always working on making solutions and mixtures. Would you want to drink milk if it was chunky? (Expect students to say no.) Milk is usually a solution but after a while begins to separate into a heterogeneous mixture. The properties of mixtures and solutions are very important to chemical engineers. These engineers need to know what chemicals are safe to mix with foods when designing fertilizers and preservative to keep food healthy for us to eat and drink. As we discussed earlier, engineers also use knowledge of mixtures and solutions when designing water treatment processes, ways to help the environment, and new medicines to help people.

Vocabulary/Definitions

concentration: Ratio of solute to solvent: the amount of material dissolved in a measure of liquid; the more material dissolved in the liquid, the more concentrated the solution.

dilute: To make a solution less concentrated, usually by adding more liquid.

dissolving: Process when two or more materials are mixed and one seems to disappear.

evaporation: A change from a liquid state into a vapor (a solid into a vapor is called sublimation); the removal of moisture or liquid.

heterogenous: Consisting of diverse or mixed ingredients

hom*ogenous: Of uniform structure or composition throughout.

mixture: When two or more kinds of matter are put together.

saturation: A solution that has reached its maximum concentration.

solute: The solid, liquid, or gas that dissolves in the liquid of a solution. The salt is the solute in a salt-water solution.

solution: A hom*ogenous mixture formed by the dissolution of a liquid, solid or gas in a liquid.

solvent: The liquid in which the solute disappears. The water is the solvent in a salt-water solution.

volume: The three-dimensional space occupied by something.

Assessment

Pre-Lesson Assessment

Brainstorming: As a class, have students engage in open discussion. Remind students that in brainstorming, no idea or suggestion is "silly." All ideas should be respectfully heard. Take an uncritical position, encourage wild ideas and discourage criticism of ideas. Have them raise their hands to respond. Write their ideas on the board. Ask:

• What are some common solutions or mixtures that you know of? (Possible answers: Powdered lemonade, Kool-Aid®, powdered iced tea, chocolate milk, gasoline, household cleaners, etc.)

Post-Introduction Assessment

Brainstorming Categories: Revisit the brainstormed list of mixtures and solutions from the Pre-Lesson Assessment. Have the students categorize the list into those which are mixtures and those which are solutions?

During Demo Predictions: While performing the introduction demonstration, ask students what will happen when you add the various other items to the glasses of water. Will you create solutions or mixtures?

Lesson Summary Assessment

Concept Juggle: Have students stand in a circle and toss the ball to each other. Each time they toss the ball, have them name a mixture. One round can be "Name a Mixture," the next round can be "Name a Solution," etc.

Engineering/Writing Application: Have students act as food engineers or biomedical engineers and write a short paragraph explaining why they need to know about mixtures and solutions in creating new food products or medicines.

Bingo: Provide each student with a sheet of paper to draw a large tic-tac-toe board (a 3 x 3 grid with 9 squares) that fills the entire paper. Have the students write a lesson vocabulary term in each square (Use the following terms: mixture, solution, solvent, solute, heterogeneous, hom*ogeneous, solid, liquid, gas). Next, have each student walk around the room and find a student who can define one vocabulary term and write the definition in the box with that term. Students must find a different student for each term. When a student has all terms completed, they can shout "Bingo!" Continue until two or three students have bingo. Ask the students who shouted "Bingo!" to give definitions of the vocabulary terms.

Lesson Extension Activities

Have students create a list of mixtures and solutions they find around their homes or the school.

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Acknowledgements

The contents of this digital library curriculum were developed under grants from the Fund for the Improvement of Postsecondary Education (FIPSE), U.S. Department of Education, and National Science Foundation (GK-12 grant no 0338326). However, these contents do not necessarily represent the policies of the Department of Education or National Science Foundation, and you should not assume endorsem*nt by the federal government.