Kids, how do you think recyclers separate all that stuff they get in their bins?  Materials can be grouped or separated by how they look and/or by the material of which they are made.  These qualities are called properties of the materials.  Some recyclers use special properties of materials to group recyclables.  In this activity, you will separate materials based on their special properties.

Please note:  All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.

You will need: a magnet, a plastic straw or coffee stirrer, blunt-end scissors, metric ruler, 1 latex balloon, 1 square of aluminum foil (5 x 5 centimeters), 1 square of paper towel (5 x 5 centimeters, cm), 5 small metal paper clips, 1 piece of window screening (20 x 30 cm), and a rectangular cake pan (about 32 x 23 x 5 cm).

Here is what to do:

1. Cut the plastic straw into five pieces (any size) using the scissors.
2. Cut or tear the aluminum foil and the paper towel into 5 pieces each (any size).
3. Roll each piece of paper towel into a ball between your thumb and index finger.
4. Place the pieces of straw, aluminum foil, paper towel, and the paper clips together in a pile on the screen.
5. Move the magnet through the pile (you may need to bring it very close to the objects). Put any objects picked up by the magnet aside in a pile. Record the objects picked up.
6. Inflate the balloon and tie it closed (your adult lab partner may need to help you). Rub the balloon back and forth on your hair. Hold the balloon close to the pile and see what happens to the objects. Put everything that is attracted to the balloon in a second pile. Record these items.
7. Now fill the cake pan with water. Take the screen with the remaining objects on it and dip it into the water so that the screen touches the bottom of the pan. Pick off any floating materials and put them in a third pile. Record these items.
8. Now lift the screen and put the remaining objects in a fourth pile. Record these items.
9. Thoroughly clean the work area and wash your hands.

Where’s the Chemistry?  Materials have different chemical and physical properties that make them easy to separate. Recycling plants use machines that vibrate to sort paper from wood and cardboard. They use magnets to pull out tin and steel that is mixed with aluminum and plastic. Paper, glass, plastic, and metal each has its own chemical make-up and its own way of being recycled. It is important that each is separated from the other items before recycling. Paper is cut up, bleached and pulped. Some metals can be picked up by magnets and other metals cannot. Some materials are attracted to each other because of static electricity, which involves positive and negative charges. The hollow plastic straw pieces float because they spread their weight out and can float on the water’s “skin.” This skin forms because water tends to stick to itself, which is called cohesion. Materials with properties that are alike get cleaned, cut up, melted down and then made into new products. Some recycling plants are starting to use these different properties to help them sort out materials. They make machines to separate out recyclable materials just like you did but their process is on bigger scale!

Be sure to do this activity with an adult!  Reuse/recycle as many of the materials as possible!  Check your reuse/recycle plans with your adult lab partner first.

--------------

Kathleen Carrado Gregar, PhD, Argonne National Labs 
[email protected]
June 2007

----------------

Reference:

American Chemical Society’s website for kids, see “Milli’s Super Sorting Challenge", at:
http://acswebcontent.acs.org/celebrate_chemistry/2007/MillisSortingChallenge.pdf