Introduction

Copper ions in solution moving between two electrodes in a magnetic field produce a swirling motion that can easily be displayed on an overhead projector.

Equations

Cu  Cu2+ + 2e-

Cu2+ + 2e-Cu

Ion Motor

To Conduct Demonstration

  1. Place some pepper on the surface of the copper sulfate solution to make it visible. 
  2. Place the apparatus on an overhead projector and focus on the floating pepper.  There should be enough solution visible between the magnets to see any movement of the pepper.
  3. Connect the positive and negative wires from a DC power source to the copper electrodes.  The solution should start to slowly rotate.  Reverse the positive and negative wires and the solution will begin to rotate in the opposite direction.  Finally, without reversing wires, turn over the magnets below the solution, thereby reversing the magnetic pole facing upwards toward the liquid.  Again, the direction of rotation should reverse.

Note:  The movement of charged particles in a magnetic field produces a force.  In an electric motor, electrons moving through the armature wires in a magnetic field produce a torque that turns it.  In this demo, the copper ions are produced at the positive electrode and move through solution to be reduced at the negative electrode.  These ions are moving through the field of the magnets situated below the copper sulfate solution; thus a torque is applied to the liquid.

Safety 

Avoid contact of copper sulfate with skin. 

Reference

Journal of Chemical Education