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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)

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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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