Beer Lambert Law: Calculate Molar Extinction Coefficient at 405nm

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Homework Statement

The p-nitrophenolate ion absorbs lights at 405nm. A solution that is 74um in the p-nitrophenolate ion was diluted 1 in 2 with water.Absorbance of resulting solution at 405nm was .650. Calculate molar extinction coefficient of the p-nitrophenolate ion at 405nm. Your meant to assume water has no absorbance at 405 nm.

How do you use the beer lambert law to predict the absorbance at 405nm of a solution that is 11.0mM in the p-nitrophenolate ion, how do you show absorbance has no units

Homework Equations

A=ecl

The Attempt at a Solution

.650 = e x 1 x (74/2)??
dont think I am right at all...

 

[Ygggdrasil]

That's the correct way to setup the equation, but you should include units so that you can get the units of ε correct (ε is usually reported in units of L cm^-1 mol^-1).