In what form (Fe3+ or FeSCN-) could iron be determined by visible spectroscopy?

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Expert Solution

The Fe³⁺ (ferric) ions and thiocyanate ions (SCN⁻) are not visible in visible region of spectroscopy.

Therefore to make the presence of these ions in solution visible, these two ions are mixed together. These two ions react with each other to form a blood-red colored complex of Fe(SCN)²⁺. By comparing the intensity of the color of this solution with the colors of a series of standard solutions, with known Fe³⁺ concentrations, the concentration of iron sample may be determined.

The reaction between ferric or iron (III) ion (Fe³⁺) and the thiocyanate ion (SCN^-) to form an intense red color complex of Fe(SCN)²⁺ and it is therefore of use in detection and quantitative estimation of trace quantities of iron(III). The reaction is shown below.

Fe³⁺ + SCN⁻ ↔ Fe(SCN)²⁺

colorless red-brown

The wavelength of light absorbed by the product Fe(SCN)²⁺will be determined from the spectral profile of FeSCN²⁺. A Beer’s Law plot will be made for a series of FeSCN²⁺solutions of known concentration. Then, the concentrations of FeSCN²⁺will be measured spectroscopically for a set of solutions made with different initial concentrations of reactants. This data will be used to determine amounts of iron (III) ion (Fe³⁺).

queen_honey_blossom answered 1 year ago

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