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Determine Molar Absorptivity

A red-colored complex PbX4 prepared from Pb with ligand X() shows promise as a means to determine trace levels of lead in the environment. The analyst prepares five standard solutions (A, B, C, D, and E) of PB: 30, 60, 90, 120, and 150 ppm, respectively. 5 ml of each solution is mixed with 5 ml of 0.10 M X. The transmittance of the five prepared solutions is measured in a 1 cm cell. A reagent blank (5 mL of distilled water and 5 mL of 0.10 M X) is used to set T = 1.00. The transmittances of the resultant solutions are 0.717, 0.543, 0.466, 0.384, and 0.259 for solutions A, B, C, D, and E, respectively.

What is the molar absorptivity (in 4 or more significant digits) of the complex?

(Assume all Pb is complexed into PbX4)

Solution Preview

To answer this question we must look at the theory behind absorption spectroscopy. The absorption of any solute in a solution is dependant on three variables: (a) the molar extinction coefficient (molar absorptivity), (b) the path length (usually 1 cm) and (c) the concentration (in ...

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