The Life and Times of Percy Julian

For Teachers

Activity 7A.3 (Lab Activity)
Separating Plastic and Metal Beads

Note to Teachers: The student version of this activity is a thought experiment that prepares them for the in-class separation as described below. Have students perform the thought experiment before the actual separation.

Lesson Overview In this activity students will learn how to separate a simple physical mixture and that the process of separating mixtures depends on differences in the properties of the components of the mixture.
Learning Objectives After doing this activity students will be able to predict how to separate other common mixtures if they are given the properties of the components (assuming the properties are significantly different).
Lesson Concepts
  1. Mixtures contain more than one kind of material.
  2. Some objects float in water and some sink.
Materials Required

Per lab group:

  • 3-oz. paper cup (1)
  • plastic beads, like those available in craft stores (20–30 or more)
  • solid steel beads (ball bearings or BBs), available in sporting goods stores (20–30 or more)

Note: The diameter of the two types of objects should be the same or similar.

Have the following readily available but not easily seen by the students:

  • a clear plastic cup or a beaker large enough to hold the bead mixture and twice its volume of water
  • water
  • a magnet

Note: This activity can be done with any spherical objects that are available in large quantities and that are not soluble in water. The important thing is that one of the objects must float in water and the other must sink.

Skills Required

Manipulative skills.

Time Required

15–20 minutes, including introduction.

Safety

Caution students not to spill the beads on the floor, as they may present a slipping hazard. They should be told to pick up any of these that they drop.

Student Ability Level and Grouping

This activity may be done by middle school students working in pairs.

Pre-lab
  1. Mix the beads in a large container.
  2. Distribute the mixture evenly among the 3-oz. cups, making sure that each group’s cup has relatively the same number of plastic and metal beads.
Procedure Notes
  1. Before students start trying to separate their mixture, require them to discuss with their partners how they will perform the separation and to record the procedure on their Investigation Record Sheet. Let them know that they can use readily available objects or substances to facilitate their separation, but do not specifically mention water or magnets. Some groups may decide to separate the beads by hand. Other groups may see that a simpler method is to add the mixture to water, or water to the mixture. In either case, the plastic beads will float and the metal beads will sink. The plastic beads can be skimmed off and dried, the water poured out of the containers, and the metal beads recovered. Do not comment on either method until after they’ve done the separation.
  2. Challenge students to separate the mixture of beads in the shortest possible time. Tell them they should end up with separate piles of plastic and metal beads at the end of the activity.
  3. Walk around the class to monitor student work and to listen to their discussion. If students request a container for water, be prepared to supply clear cups or beakers and water.
  4. If you have done Activity 7A.2, Separating Coins with your class, and the students discussed magnets as a possible method for separation, they might suggest that a magnet would be a good way to separate the metal beads from the plastic ones. Have magnets ready, just in case.
Post-lab
  1. When groups have finished, ask for volunteers to describe how they did the separation.
  2. By discussion, lead students to the idea that this separation (and all separations) depends on a difference in the properties of the components. If students separated the beads by hand, the property is either the color or the size of the spheres. For those students who did the separation by adding water, the property is the density of the beads and BBs.
  3. Require students to record their results and the central concept on their Investigation Record Sheet.
Assessment See Activity 7A.7, Assessment: A Challenging Separation.

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