Activity 7A (Lab Activity Series)
Pure Substances, Mixtures, and Separations
This series of activities focuses on the separation of mixtures. The activities can be used in a unit on mixtures and pure substances.
In the student version of this activity, the student is asked to do a brief introductory reading and then perform three thought experiments that correspond to the first three in-class activities outlined below (7A.1–3). You can assign your student one, two, or all three of these thought experiments to get them thinking about mixtures and separations in preparation for in-class activities and discussion.
In addition, we provide you, the teacher, with several lab activities to be done in class. You do not have to use all the lab activities provided below. Several are presented so that you can choose the ones that best fit your needs.
Activity 7A.1. Separating Marbles
Activity 7A.2. Separating Coins
Activity 7A.3. Separating Plastic and Metal Beads
Activity 7A.4. Separating a Salt and Sand Mixture
Activity 7A.5. Magnetic Separation
Activity 7A.6. Separation by Paper Chromatography
Activity 7A.7. Assessment: A Challenging Separation
Notes on Using These Activities
If you want students to understand the concept that physical separations are based on the components in the mixture having at least one property that is different from the other components, then it is important to do Activity 7A.1 first, since it provides a mechanical model that is easy for students to see and understand. The assessment activity (7A.7) should be used after students have performed several other separations.
You can delay more in-depth discussion and use of the traditional vocabulary terms presented until students have gained some experience with separations. The need for definitions and vocabulary will emerge naturally from students’ working with mixtures.
You can present each of these activities as a challenge to students. Some students will know from experience or prior knowledge how to perform some of the separations. The marble separation (7A.1) can be used to engage students with the idea of separations, since there is more than one way to perform the separation. Regardless of which method is chosen, the separation depends on the components’ properties being different. That is the central concept we want students to learn in these activities, and in your discussion of the activities you should remind students of this.
Prior to beginning each new separation, you should challenge students to apply what they learned in previous separations. You should be reminding students to apply the central concept to the new separation. As students do more separations you should be monitoring their ability to plan each new separation by asking, “What property can we use to separate this mixture?” This kind of student thinking will allow you to discuss with the class topics like properties of matter, pure substance, mixtures, and types of mixtures. The activities require lab skills which should also be part of the student learning.
As students become increasingly able to perform more complex separations, you can increase the complexity of the tasks. Here are some suggestions:
- present a mixture to students without identifying the components;
- present a sample to students without indicating whether it is a single substance or a mixture;
- require that the separations be quantitative; requiring students to return to you masses of components equal to the masses in the original mixtures allows you to challenge all students.
You might also use each of these activities (after the first two or three) as formative assessments. By providing the activity as a challenge, you can monitor whether students are learning the central concept.
You might challenge students to see which group can perform the bead separation (7A.3) most quickly or efficiently or completely. This kind of challenge might lead students to consider the density of the beads, which would lead to a rapid separation.
This series of activities meets the following National Science Education Standards (Grades 5-8) and Curriculum Standards for Social Studies.
National Science Education Standards (Grades 5-8)
Unifying Concepts and Processes
Science as Inquiry
Science and Technology
History and Nature of Science
Curriculum Standards for Social Studies