Report 8 - Vincent Gallo CHM-3120C-903 Lab 8...

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Vincent Gallo CHM-3120C-903 Lab 8 Spectrophotometric Determination of Iron in Mohr’s Salt with Phenanthroline March 28 th 2016
I. Introduction Spectrophotometric techniques are commonly used in analytical experiments in order to determine the concentration of different solutes in solution. Spectrophotometry uses the dual nature of light both as a particle and a wave so that the absorbance reading of a solution can be determined. Absorbance is crucial because it is directly proportional to concentration. Beer’s-Lambert law incorporates the relationship between absorption and concentration so that either of the two and or molar concentration can be found via this equation: A = εlc Beer’s law works for monochromatic radiation passing through a dilute solution in which the absorbing species is not participating in a concentration-dependent equilibrium. The color of a solution is the complement of the color of the light that it absorbs. The color we perceive depends not only on the wavelength of light but also on its intensity. In this experiment, a bidentate ligand, o -phenantrholine will react with iron (II) to form a complex ion. It is important to note that a bidentate ligand is a lewis base that donates two pairs of electrons to a metal atom. In this case, o -phenanthroline interacts with a divalent iron atom in solution the reaction seen below: phen ¿ ¿ + ¿ + ¿ ↔Fe ¿ Fe ( II ) + 3 phen H ¿ Iron in its ferrous state has a maximum absorbance reading at a wavelength of 508nm. Several trials incorporating different volumes of stock solution will provide a linear
relationship between absorbance and concentration that can be illustrated on excel. This linear function can be utilized to determine the concentration of the unknown, which is the basis of this experiment.

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