For this experiment, why was it not necessary to convert absorbance to concentra

Question

For this experiment, why was it not necessary to convert absorbance to concentration before doing first and second order calculations and graphs? Why was 590 nm used as the wavelength? Explain specifically what advantage was gained by using this wavelength. Calculate the volume of a 2.0 times 10^-4 M crystal violet solution needed to prepare a 100.0 mL solution with a final concentration of 5.0 times 10^-6 M. Explain why spectroscopy was a good method for analyzing the kinetics of this reaction.

Explanation / Answer

(1)

This is because Absorbance is directly proportional to concentration, as expressed in Beer Lambert's law :

A = e*l*c

So converting A to c is not really necessary.

(2)

This particular wavelength falls in green portion of the visible spectrum.

Crystal violet appears purple because it absorbs green while reflects blue and red. Thus its essential to set the wavelength for absorbance in the green portion.

(3)

Dilution factor = 2*10-4 / 5*10-6 = 40

Thus, take 2.5 mL of 2*10-4 M CV solution and dilute it to 100 mL.

(4)

Absorbance is linearly related to concentration, so spectroscopy makes calculations easier. Also in this reaction, since the absorption occurs in the visble portion of spectrum, spectroscopy is further favored due to this.

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