Question

Write down 7 facts or statements about the following; To measure the iron in vegetables, iron must be extracted and complexed with 1,10-phenanthroline to create iron(II)tris(phenanthroline). An aliquot of a 50 mL sample measured in the lab was found to have an absorbance of 1.02 when measured in a cell with a path length of 1.00 cm. The molar absorptivity of iron(II)tris(phenanthroline) at 508 nm is 1.11 x 104 M-1cm-1.

Answer 1

The amount of iron present in a sample is quantitated by first reacting the iron with 1,10-phenanthroline to form a colored complex and then measuring the amount of light absorbed by this complex. Beer's law can then be used to determine the concentration relative to absorption. To form a complex, the iron must be first reduced to its ferrous state. This is done by reacting the iron with hydroxylamine hydrochloride by the following reaction:

2 Fe³⁺ + 2 NH₂OH + 2 OH^- ====> 2 Fe⁺² + N₂ + 4 H₂O Once a colored complex is formed, the wavelength of light which is most strongly absorbed is found by measuring the absorbance at various wavelengths between 400 - 600 nm. After the most suitable wavelength is determined, a series of iron standards is measured at this wavelength and a calibration plot of absorbance vs. concentration is prepared. The absorbance of the unknown sample is measured and the calibration curve is used to calculate the concentration of iron in the sample