S170: Chemical Rxns – Complex Ions – Invisible Signs

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)₆^4- → Fe₂(CN)₆^-(s)

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: ~10 minutes

Safety 

Eye protection should be worn to prevent spray from getting in eyes. 

Acknowledgment

Margaret Asirvatham, Spring 1995
Lora Ruffin and Michael Polk, Summer 2009