Gurvinder Kaur¹, Sumanjeet Kaur¹, Tribhuvan Kumar Pathak¹, Vandana Sharma^1,, Kartikay Tyagi¹

The determination of stoichiometry and stability constant of metal-ligand complex holds great significance for chemical, physical, environmental and biological studies. In the present work, the stoichiometric ratio and stability constant of iron complex of 3,5-dinitrosalicylic acid was determined using Job’s method of continuous variation. Job’s method can be easily applied to investigate a wide range of colored complexes including mononuclear as well as polynuclear complexes of various species, therefore showing its usefulness for practical application in undergraduate University curriculum. The stoichiometry of the major complex formed was determined to have a 1:1 ratio of Fe⁺² and 3,5-dinitrosalicylic acid. Stability constant value was determined and found to be 3 x 10⁵. The resulting high stability of the complex can be attributed to resonance stabilization of metal-ligand П-bonding electron density. From the thermodynamic parameter, the negative value of overall change in Gibb’s free energy shows the complex formation between Fe⁺² and 3,5-dinitrosalicylic acid is spontaneous and feasible.

absorption spectra, stability constant, stoichiometry, 3，5-dinitrosalicylic acid, continuous variation method, transition metal complex