Summary

In this lab, students investigate the composition of a given mixture. Using their content knowledge and a variety of provided materials, students are tasked with separating the mixture into its individual components.

Grade Level

High School and Middle School

NGSS Alignment

This lab will help prepare your students to meet the performance expectations in the following standards:

• Scientific and Engineering Practices:
  • Planning and Carrying Out Investigations
  • Constructing Explanations and Designing Solutions

Objectives

By the end of this lab, students should be able to:

• Work collaboratively with peers to develop a detailed lab procedure to follow during an experiment.
• Evaluate and distinguish between components of a mixture based on physical properties.
• Separate the components of a mixtures by applying fundamental understanding of chemistry concepts.

Chemistry Topics

This lab supports students’ understanding of:

• Mixtures
• Separating Mixtures
• Physical Properties

Time

Teacher Preparation: 30 minutes

Lesson: 60-90 minutes

Materials (per group)

• Container with mixture  (~1 cup)
  • sand, iron filings, salt, and aquarium gravel              
• Spoons                                           
• Forceps/tweezers                                                
• Filter
• Magnets
• Magnifying Glass
• Hot plate
• Water
• Funnel  
• Tray                  
• Beakers    
• Cups
• Ziploc Bags     
• Wooden Stirrers

Safety

• Always wear safety goggles when handling chemicals in the lab.
• Students should wash their hands thoroughly before leaving the lab.
• When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.
• Exercise caution when using a heat source. Hot plates should be turned off and unplugged as soon as they are no longer needed.

Teacher Notes

• This lab was designed as an inquiry-based formative assessment. To learn more, read the associated article, An Inquiry Activity: Mixture Separation Challenge, published in the September 2021 issue of Chemistry Solutions.
• Prior to completing this lab, my students had hands-on lab experience with topics such as chromatography, Tyndall effect, magnetism, boiling, and crystallization.
• I suggest that students work in small groups of two or three in order to complete this challenge. This allows each student to have a voice in the procedure, whereas larger groups might hinder that collaboration.
• I use this activity with high school students, but it could be easily modified for use in middle school. The materials are easily accessible and safe to use for middle school students. However, if a hot plate is used, the teacher may want to facilitate that station, and directly supervise the students’ activity.
• For this lab, I create a mixture of sand, iron filings, salt, and aquarium gravel, but I do not tell my students what the mixture is composed of. I give each student group a cupful of the mixture and ask them to make notes of their observations on the student handout. Students can using a wooden stick, spoon, or magnifying glass. I also allow students to touch the mixture or shake the container.
• After the student groups examine the mixture, I ask them to share their initial observations with the whole class and then ask students to provide guesses as to what materials they thought were in the mixture.
• Then I explain the actual composition. The aquarium gravel and the sand are usually the easiest parts of the mixture for students to identify; on the other hand, many groups were not able to visually identify the black flakes as iron filings, or the white powder as salt. Knowing the composition of the mixture is important, because this information will help them develop experimental procedures for separating the mixture. This understanding also allows students to apply their prior knowledge and familiarity with the properties of each component.
• The goal of the activity is to have students apply their content knowledge to the separation task. Prior to starting, the only prompt that I provide to students is, separate the mixture. Students use the lab handout to record their procedure, results, and reflection. When each student group feels comfortable with their procedure, they can start.
• I encourage teachers using this lab to serve as a facilitator, and refrain from interjecting. Each student-developed procedure has merit. Allow student groups to feel safe and comfortable in testing their ideas through trial-and-error, iterating on their lab procedures and design process as needed.
• Provide variety of materials that students can choose from in their planning. Suggestions are given in the materials section, but others can be added or students could be allowed to request specific items. Additionally, the mixture can be modified from the description given.
• I suggest using a portable work surface, like a plastic lunch tray, to contain the mess during this lab. *Make sure students don’t let the tray come in direct contact with the hot plate!
• After the groups have carried out their procedure, I allow each group to informally share their ideas with the class as a lab “gallery walk.” This helps students in the class to visualize the results, and to see which parts of the mixture each group was able to separate. As a class, we travel from table to table, circling around each team’s table while the group explains their procedure and shares out results.
• It is important to make sure that students realize that each group will have different results. On the student lab sheet, I provided the opportunity for reflection, so that students can share which parts of their procedure was successful.
• In separating this mixture, ideally the students would start off by manually picking out the aquarium gravel. Next, students can attempt to remove all of the iron using a magnet. Wrapping the magnet in something like a plastic bag will prevent the iron from sticking to the magnet during this process. The remaining mixture will contain sand and salt. Water can be stirred into the mixture, allowing some salt to dissolve into the water. This saltwater mixture can be decanted or filtered off using a funnel and filter paper. That step of the process may need to be repeated to ensure that most of the salt is removed. Any remaining saltwater and sand can be heated to evaporate the remaining water, or the sand can be spread out on a paper towel or tray to dry.