Expt 008 -- One Dollar's Worth of Iron

Description

Paper dollar bills are printed with magnetic inks. This can be shown by dangling a dollar bill in one hand, and showing how the bottom end can be moved when a strong magnet is brought near. This can be followed by the extracting the magnetic ink from the bill using a blender and a magnet. Students are surprised when you destroy money--the sample for analysis. This destruction is the dilemma encountered with most analyses--for example, authenticating art masterpieces or an artifact such as the Shroud of Turin. Students are also amazed at how much iron is in a single dollar bill.

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 to separate components in a mixture.
  3. A homogeneous mixture is one in which the components are evenly distributed. A heterogeneous mixture has uneven distribution of its components.
  4. Iron in elemental form is strongly attracted to magnets. Compounds of iron are not as strongly attracted to magnets.
  5. Analyzing a sample frequently changes the sample irreversibly.

Safety

Use ordinary laboratory safety procedures.

Procedure

Demonstrate the magnetic properties of a dollar bill by dangling a dollar bill in one hand, and showing how the bottom end can be moved when a strong magnet is brought near.

!!!Click here to See Movie.

  1. Add about 200 mL of water to a blender. Start the blender.
    crumple a dollar bill. Throw it into the blender. Blend for 3-4 minutes.
    !!!Click here to See Movie.
  2. Hold the magnet to the outside of the blender while it is whirling. Stop the blender.
    !!!Click here to See Movie.
    Then withdraw the magnet to show the black ink spot that gathered there. A white plastic spoon behind spot displays the dark color.
    !!!Click here to See Movie.
    If the blender wall is too thick or if the magnet is too weak, pour the dollar bill slurry into a clear plastic cup and stir it with a white plastic spoon while the magnet is pressed to the side of the cup.
  3. Pull the black ink spot about with the magnet. Move the magnet a cm to one side.
  4. To accentuate the spot and to keep it from dispersing too quickly, press the back of the plastic spoon up against the spot from behind and then lift the magnet aside. If one wishes to remove the ink spot, re-position the magnet and then slowly lift it up (while stirring) to bring the spot up to the surface of the slurry. Then scoop the spot out with the tip of the spoon.
  5. The spot of iron may also be dissolved in 10 mL of 1.0 M HCl and then tested for iron with the addition of a few mLs of 1.0 M KSCN.
    Or, do a spot test on the overhead using an acetate sheet or a 24-well plate. Put a few flakes of iron on the sheet; add 10 drops of 1.0 M HCl and stir; add a 2 or 3 drops of 0.1 M KSCN.
    !!!Click here to See Picture.
    !!!Click here to See Movie.

Questions

  1. What evidence is there that the ink in a dollar bill is made of iron, instead of some other metal?
  2. Is the iron in currency present as ions or elemental iron?
  3. State any advantages to having magnetic materials in currency.

Handout Makeup

Name ___________________________ Class _______

Teacher __________________________

BeckerDemos 008 One Dollar's Worth of Iron

Watch the movies.

  1. Describe the iron extracted.
  2. Answer the questions.

Curriculum-

This activity works well early in the semester when discussing chemical and physical separations or heterogeneous mixtures. This activity also ties in well with units on magnetism or analysis. The procedure illustrates a problem of many analytical methods. The sample is destroyed by the analysis.

Activity-

Demonstration - Student or Teacher

This activity works best as a teacher demonstration. Attention is enhanced by the surprise of destroying money.

Safety-

Use ordinary laboratory safety procedures.

Time-

Teacher Preparation: 2 minutes

Class Time: 5 minutes (If you weigh the iron, you must allow time for the iron to dry and go back to it.)

Materials-

Optional:

Disposal-

Pour the slurry onto a paper towel in the bottom of the sink to trap any large pieces. Dispose of the paper with ordinary trash. If the BeckerDemos overhead technique is used for the iron test, wipe with a paper towel and dispose with ordinary trash; otherwise, neutralize the iron test solution, and flush down the sink with running water.

Lab Hints-

This demonstration requires a blender in the classroom. The novelty of destroying money in front of the students grabs their attention. The demonstration is most effective if the dollar bill has been "borrowed" from an unknowing student in the class. (Ask for the dollar bill before the students see the blender or you may have very few volunteers!) Once the blender has been turned on, the distraught student can be comforted with such remarks as "Don't worry, I'm just increasing your liquid assets!" or "Just think, you'll never have a problem with cash flow again!"

Observations-

Answers-

Q1. What evidence is there that the ink in a dollar bill is made of iron, instead of some other metal?
A1. The ink is strongly attracted to a magnetic field. Iron is one of only a few metals that is so attracted. And of the magnetic metals, iron is the only one that forms a red complex with thiocyanate (SCNÑ) ions.
Q2. Is the iron in currency present as ions or elemental iron?
A2. Elemental iron. The ions are not that strongly attracted to a magnetic field.
Q3. State any advantages to having magnetic materials in currency.
A3. The bill may be read by machines more easily. It may also help prevent counterfeiting.

Key Words 1-

separation, heterogeneous mixture, mixture, magnet, analysis