Expt 006 -- Cereal Flake Races

Description

Many breakfast cereals contain trace amounts of iron in its elemental form. Flakes of these cereals can be floated on water in a petri dish on the overhead projector and moved about by a strong magnet.

Chemical Concepts

  1. Physical properties are maintained by the individual components in a mixture.
  2. This conservation of properties may often be taken advantage of when separating mixtures into their components.
  3. A homogeneous mixture is one in which the components are evenly distributed. A heterogeneous mixture has uneven distribution of its components. Breakfast cereals serve as good examples of heterogeneous mixtures.

Safety

No special precautions are required.

Procedure

  1. Take out a box of iron-fortified cereal and pose the question: This cereal claims to contain iron; should it not then be attracted to a magnet? After some discussion, place a flake on the overhead projector, and ask what the students think will happens when the magnet is brought near to it. After they have made their predictions, bring the magnet near and observe. (Nothing happens.)
  2. After discussing why nothing happened (flake was too big... not enough iron... too much friction... not a strong enough magnet...) ask what might be done to overcome some of these problems -- hopefully, someone will suggest the idea of floating the flake.
  3. Place the petri dish on the overhead and pour in enough water to fill it completely. Add a little more water with a dropper so that the surface is domed slightly above the rim of the dish. Surface tension effects interfere if the water is not above the rim.
  4. When the water has stopped swirling, place a small flake or piece of a flake (approximately 1 cm in diameter) in the center. Bring the pole of the magnet nearby and observe. Move the magnet slowly in one direction. Then move the magnet slowly in a different direction to show that the flake attracted to the magnet. Keep the flake away from the edges of the dish where surface tension effects may interfere.
    !!!Click here to See Movie.
  5. Place the flake in the center of the petri dish. Place the magnet about a centimeter away. Wait and observe. Move the magnet away as the cereal approaches.
    !!!Click here to See Movie.

Note:

Again, the magnet must be a rather strong one, and must be held steadily within a few millimeters of the flake. Furthermore, some flakes, by chance, have a higher iron content than others, so if at first you don't succeed... Also note: after 30-40 seconds, the flake becomes water-logged and too sluggish to show much movement.

Handout Makeup

Name ___________________________ Class _______

Teacher __________________________

BeckerDemos 006 Cereal Flake Races

Observe the movies.

Describe what happens to the cereal flakes.

Curriculum-

This activity ties in well with units on magnetism, friction and forces, and foods and dietary requirements.

Activity-

Laboratory or Demonstration or Home Experiment

As above, this activity works well as a demonstration for the overhead projector, but it could also be done individually by the students if sufficient magnets and time were available.

Safety-

No special precautions are required.

Time-

Teacher Preparation: 1 minute

Class Time: 5-10 minutes

Materials-

Disposal-

No special precautions are required.

Observations-

One should be able to observe movement of the flake toward the magnet. This, of course, is due to the attraction between the magnet and the small pieces of iron in the cereal. Even with a rather strong magnet, though, this force is still very weak (there is relatively little iron present in just one flake). Thus when the flake is sitting on the glass screen of the overhead projector, the force is not great enough to overcome the friction between the flake and the glass. Floating the flake on water reduces this friction, and allows the attractive force to accelerate the flake across the dish.

Key Words 1-

magnet, magnetic, iron