(Solved): Ortho-phenanthroline reacts with ferrous ion to produce a deeply colored complex with a molar absor ...

Ortho-phenanthroline reacts with ferrous ion to produce a deeply colored complex with a molar absorptivity \( (\varepsilon) \) of \( 11,100 \mathrm{~L} / \mathrm{mol}^{-1} \mathrm{~cm}-1 \) at a \( \lambda_{\max } \) of \( 508 \mathrm{~nm} \). You diluted the stock colored complex that you were provided using a 4 fold serial dilution. You measured the third dilution in the series in a plastic cuvette with a pathlength of \( 0.5 \mathrm{~cm} \) at \( 508 \mathrm{~nm} \) and obtained an absorbance of \( 0.73482 \). What was the concentration of the original stock solution in \( \mathrm{mM} \) ?