The Iron(III) Thiocyanate Reaction: Research History and Role in Chemical Analysis

Abstract

The reaction between ferric ion and thiocyanate ion has been understood differently throughout its 191-year history from the time JBerzelius (1779-1848) first observed the resulting deep red coloration to more recent times when sophisticated data analysis has been applied to unlock constants related to its kinetic and equilibrium behaviour. The reaction was first seriously studied in 1855 by John Hall Gladstone (1827-1902) to help resolve a controversy between the Swedish chemist, Torbern Olof Bergman (1735-1784) and the French chemist, Claude Louis Berthollet (1748-1822). Even before the concept of chemical equilibrium was understood the reaction was used in chemical analysis. Eventually its chemical equilibrium properties were harnessed by the chemistry education community to the extent that it began to appear in chemistry textbooks and laboratory manuals. The reaction was used historically to highlight the nature of a chemical reaction and can be used to draw attention to the laws of chemistry, the models and theories of chemistry, chemical nomenclature, mathematics and data analysis, and instrumentation, which are important ingredients of what one might call the nature of chemistry. An historical investigation of this reaction helps one to determine how chemistry develops its knowledge base; how it assesses the reliability of this knowledge base; and how some important tools of the profession have been brought to bear on a chemical reaction to achieve understanding, a worthwhile goal of any historical investigation. While physics and astronomy achieved the status of exact sciences in the 17th and 18th centuries, it wasn’t until the 20th century that chemistry was able to approach this status with the tools of mathematics and data analysis applied to the complex nature of a chemical reaction.