Introduction

A pale orange solution is sprayed onto a sheet of seemingly blank, white paper.  Dark red and blue lettering appears.

 

Fe3+ + SCN- → FeNCS2+ (dark red)

Fe3+ + Fe(CN)64- → Fe2(CN)6-(s) (blue)

Supplies

Short List

  •   3M chromatography paper or bench paper
  •   Artists’ paint brush

Chemicals

  •   0.2M KSCN solution
  •   0.2M K4Fe(CN)6 solution
  •   0.1M Fe(NO3)3 solution

Prior to Lecture  (prep time ~ ? min.)

1.      Prepare the following chemicals:

  0.2M KSCN solution in an ointment jar.

      1g of KSCN in 50mL of water

  0.2M K4Fe(CN)6 solution in an ointment jar.

      4.2g of K4Fe(CN)6 in 50mL of water.

  0.1M Fe(NO3)3 solution and place in a spray bottle

      4g of Fe(NO3)3 in 100mL plus enough nitric acid to make solution colorless.

2.      Using artists’ paint brushes, paint desired message on a large sheet or roll of paper (3M chromatography paper works well for small lecture rooms and bench paper works well for larger rooms), using KSCN where red is desired and K4Fe(CN)6 where blue is dsired.  Dip brushes often to transfer as much solution as possible to the paper.

3.      Allow the paper to dry completely and hang it up.  Large sheets of plastic or plastic garbage bags should be used to protect any sensitive surfaces under or behind the sign.

To Conduct Demonstration

  1. Spray dilute, acidic Fe(NO3)3 solution onto paper that has been painted with dilute KSCN and K4Fe(CN)6 solutions and allow to dry.

Demo Time: ~? minutes

Safety and Disposal

Eye protection should be worn to prevent spray from getting in eyes.  Completed sign may be thrown away after it dries.