Paramagnetic Metal Ions

Introduction

Several transition metal salts are affected by a strong magnet. Students are generally familiar with the fact that metallic iron is magnetic, but the science behind this observation is not necessarily understood. Paramagnetic salts generally contain transition metal ions that have at least one unpaired electron in their electron configuration. In this demonstration, a neodymium magnet is used to deflect small v-shaped chambers containing paramagnetic transition metal salts.

Concepts

• Paramagnetism
• Electron configuration
• Diamagnetism
• Orbitals

Materials

Safety Precautions

Copper(II) sulfate is a skin and respiratory irritant and is moderately toxic by ingestion and inhalation. Manganese(II) sulfate is a body tissue irritant. Zinc sulfate is an irritant and is slightly toxic. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Please review current Safety Data Sheets for additional safety, handling and disposal information. Wash hands thoroughly with soap and water before leaving the laboratory.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. Calcium sulfate, copper(II) sulfate, and zinc sulfate may be reused or placed in the trash according to Flinn Suggested Disposal Method 26a. Manganese(II) sulfate may be reused or disposed of properly by a licensed removal company according to Flinn Suggested Disposal Method 27f.

Prelab Preparation

1. Use scissors to cut the stems of two pipets 1" from the tip of the pipet. The pipets should fit snugly around the pipet elbow (see Figure 1).
   {13851_Preparation_Figure_1}
2. Fill each bulb of the two pipets with 2 g of copper(II) sulfate, CuSO₄.
3. Slip the filled pipet stems over the plastic elbow (see Figure 2).
   {13851_Preparation_Figure_2}
4. Repeat steps 1–3 using manganese(II) sulfate, MnSO₄•H₂O, zinc sulfate, ZnSO₄, and calcium sulfate, CaSO₄.
5. Cut four six-inch pieces of thread. Tie a piece of thread around the elbow of each pipet assembly.
6. Clamp the dowel rods to the utility clamps (see Figure 3).
   {13851_Preparation_Figure_3}
7. Attach the utility clamps (with dowel rods) to the ring stand (see Figure 4).
   {13851_Preparation_Figure_4}
8. Suspend the filled pipets by attaching the thread to the hooks on the dowel rods (see Figure 5). The pipets should hang evenly.
   {13851_Preparation_Figure_5}
9. Cut out the ions from the Ion Identification Card Sheet. Attach each ion card to the dowel rod in the appropriate position using the provided Velcro dots (see Figure 5).

Procedure

Bring a neodymium magnet near each one of the suspended pipets. Observe how the different salts respond to the magnet.

Student Worksheet PDF

13851_Student1.pdf

13851_Teacher1.pdf

Teacher Tips

• The chemicals in this kit may be stored in the pipet assemblies and reused as many times as desired.

Further Extensions

• As an extension, have students fill out the given Electron Configuration Worksheet for each ion. Make one copy of the worksheet for each student. You may wish to make an overhead transparency of the given Teacher Electron Configuration Chart and follow along or help guide the students on the overhead projector transparency. Following is a sample completed electron configuration for Ca²⁺.
  {13851_Tips_Figure_6}
• Have students discuss why some materials are paramagnetic and others are not.
• The magnetism of other salts may be experimented with as well. Extra pipets are available from Flinn Scientific (Catalog No. AP8480).
• A video presentation of the Paramagnetic Transition Metal Ions activity is available through the Flinn Scientific website (www.flinnsci.com) in Electron Configuration, part of the Flinn Scientific—Teaching Chemistry™ eLearning Video Series.

Discussion

The pipets containing the manganese and copper salts will be influenced by the strong magnet, while the other two pipets will be unaffected by the magnet. The explanation for these observations lies in the electron configuration of the transition metal cations in each salt. The manganese ion has five unpaired electrons while the copper ion has one unpaired electron. Not surprisingly, the magnetic attraction of the manganese ion is much stronger since it has more unpaired electrons. The other metal cations possess no unpaired electrons and are not affected by a magnetic field.

Atoms or ions that have only paired electrons (i.e., no unpaired electrons) are essentially unaffected by a magnetic field. These atoms or ions are classified as diamagnetic. The magnetic moments of the paired electrons are effectively canceled out.

A paramagnetic substance is defined as possessing at least one unpaired electron. In a paramagnetic solid, the unpaired electrons of the atoms or ions are not influenced by the electrons on adjacent atoms or ions. The magnetic moments on the individual ions are randomly oriented. However, when subjected to a magnetic field, the magnetic moments become aligned roughly parallel to each other, producing a net attractive interaction with the magnet.

A ferromagnetic substance is much more strongly affected by a magnetic field. Ferromagnetism occurs when the unpaired electrons of the atoms or ions in a solid sense the orientations of electrons of the neighboring atoms or ions. The most stable or lowest energy arrangement occurs when the spins of the electrons on adjacent atoms or ions are aligned in the same direction. The attraction of a ferromagnetic compound for a magnet may be as much as one million times greater than that of most paramagnetic substances.

Electron configurations of selected ions

• Ca²⁺ 1s²2s²2p⁶3s²3p⁶ (diamagnetic)
• Cu²⁺ 1s²2s²2p⁶3s²3p⁶4s⁰3d⁹ (paramagnetic, 1 unpaired e^–)
• Mn²⁺ 1s²2s²2p⁶3s²3p⁶4s⁰3d⁵ (more paramagnetic, 5 unpaired e^–)
• Zn²⁺ 1s²2s²2p⁶3s²3p⁶4s⁰3d¹⁰ (diamagnetic)

References

Flinn Scientific would like to thank Jeff Bracken, chemistry teacher at Westerville North High School in Westerville, Ohio, for sharing this original idea. Jeff Bracken would like to thank his student lab assistant, Matt Cocuzzi, for his assistance with the development of this chemical demonstration.

Brown, T. L.; LeMay, H. E.; Bursten, B. E. Chemistry: The Central Science, 5th Ed., Prentice Hall, 1991, p 891–892.

Burke, J. A. J. Chem. Educ. 1972, 49, 568.

Cortel, A. J. Chem. Educ. 1998, 75, 61–63.

Gross, G. R.; Bilash, B.; Koob, J. K. A Demo A Day. Flinn Scientific, Inc. 1995, p 124.

Marzzacco, C. J. Chem 13 News, January, 1999, p 16.