The Life and Times of Percy Julian

For Teachers

Activity 7A.1 (Lab Activity)
Separating Marbles

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

Lesson Overview

This activity provides a model for separation techniques, including

  1. hand-sorting
  2. filtering
  3. shaking and settling.
Learning Objectives Students will learn the physical principles behind separation by means of hand-sorting, filtering media, or shaking to cause the settling of particles based on density and/or size differences.
Lesson Concepts
  1. The process of filtering to separate substances with different size particles requires a barrier that is selective in terms of what size particles can pass through.
  2. If the mixture is shaken in place, particles will settle out in layers depending on their density and size.
Materials Required
  • Large marbles (20–40)
  • Small marbles (50–75)
  • A large plastic container to hold all the marbles
  • Two spare plastic containers to hold the sorted marbles as needed

For Filtering Method A:

  • Marbles as indicated above
  • Two 1-pt. clear, plastic, cylindrical deli containers with lids
  • One 1-qt. clear, plastic, cylindrical deli container (the 1-pt. containers should be identical and should fit inside the top of the 1-qt. container and stay suspended there)
  • Drill with bit larger in diameter than the small marbles, but smaller in diameter than the large marbles. A wood bit works well.

For Filtering Method B (if deli containers or drill with bit are not available):

  • Marbles as indicated above. The small marbles (or BBs) should be small enough to go through a hole the size of a paper punch hole.
  • 1-qt. wide-mouthed glass jar with open-ring lid
  • Cardboard, cut to fit inside open-ring lid
  • Paper punch to punch holes in cardboard
Skills Required Students should be able to carefully manipulate breakable equipment (glass jar and marbles) if you involve them hands-on in the demonstration.
Time Required Maximum of 30 minutes.
Safety Students should be careful in handling marbles in class (so they don’t roll around and cause an accident). Be aware of the potential for breaking glass jars when loading them with marbles. Students should wear safety goggles.
Student Ability Level and Grouping

This middle school activity may be done as a demonstration by the teacher. (It could also be adapted as a whole-class laboratory activity.)

Pre-lab

Decide on Filtering Method A or B, depending on your resources.

For Filtering Method A:

Drill holes (gently) in the bottom of one of the 1-pt. deli containers. The drill bit size should be larger than the small marbles, but smaller than the large marbles. This container will be your “filter.”

For Filtering Method B:

Cut cardboard to fit inside the open-ring lid of the glass jar. Punch holes in the cardboard. Secure the cardboard so it fits snugly in the lit. This makeshift cardboard lid will be your “filter.”

Procedure Notes

The procedures below are described as teacher demonstrations, with some individual student help. (They could be easily adapted as a whole-class laboratory activity with minimal difficulty.)

  1. Hand-Sorting
    1. Fill your large plastic container with all the marbles. Ask a student to separate them by hand into the two spare containers—this can be tedious!
    2. Return all the marbles to the large container.
  2. Filtering
    Filtering Method A
    1. Place the filter (the one with holes) container inside another 1-pt. container. This will hold the marbles and prevent their falling out until you’re ready to do the separation.
    2. Fill the filter container about half-full with a mix of marbles of two different sizes.
    3. Now remove the second, outside container, leaving only the filter container with marbles. Be careful not to allow any of the smaller marbles to escape through the bottom holes (or pick them up if they do!).
    4. Place the lid on the filter container and place it inside the 1-qt. container.
    5. Ask a student to shake the contents. The small marbles will fall through the holes in the filter container into the bottom (1 qt.) container, but the large marbles will remain trapped inside the filter container.
    6. Return all the marbles to the large container.

      —OR—

    Filtering Method B

    1. Fill the glass jar about half-full with a mix of marbles of two different sizes.
    2. Place the lid you made (with the holes punched in it) on the jar.
    3. Ask a student to pour the contents into one of your spare containers. The small marbles will fall through the holes in the lid, but the large marbles will remain trapped inside the jar.
    4. Return all the marbles to the large container.
  3. Shaking and Settling
    1. Fill your 1-qt. container about half-full with a mix of marbles of two different sizes.
    2. Ask a student to put the lid on and shake. The smaller marbles will move toward the bottom, while the larger marbles will migrate toward the top, oddly enough.

Have the students record their observations on the Investigation Record Sheet for this activity.

Assessment See Activity 7A.7, Assessment: A Challenging Separation.

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