Determination of composition and stability constant of iron sulfosalicylate complex

The composition and stability constant of iron (Ⅲ) sulfosalicylate complex were determined as follows:

Objective: To understand the principle and method of spectrophotometric determination of complex composition and stability constant. Determination of ph value

Sulfosalicylic acid can form a stable complex with Fet, and the composition of the complex is different because of the different pH value of the solution. In this experiment, pH

Spectrophotometry is usually used to determine the composition of complexes.

When a beam of monochromatic light with a certain wavelength passes through a colored solution, part of the light is absorbed by the solution and part of the light passes through the solution.

Isomolar series method: that is, using monochromatic light with a certain wavelength, the absorbance of a series of solutions with changing components is determined (the total amount of central ion M and ligand R remains unchanged, while the molar fraction of M and R changes continuously).

Obviously, in this series of solutions, there are some solutions with excessive metal ions. And other solution ligands are also excessive; In these two solutions, the concentration of coordination ions can not reach the maximum: only when the molar ratio of metal ions to ligands in the solution is consistent with the composition of coordination ions can the concentration of coordination ions reach the maximum.

Because central ions and ligands hardly absorb light, the greater the concentration of coordination ions, the greater the absorbance of the solution. Generally speaking, at a specific wavelength, the absorbance A of a series of solutions composed of [r]/{m]+[r] is measured and the curve of A-[r]/([m]+[r] is drawn, and there must be a maximum value in the curve.