Dr. Nickolaisen set up an absorption apparatus on the roof the old Physical Scie

Question

Dr. Nickolaisen set up an absorption apparatus on the roof the old Physical Sciences building to measure the amount of NO_2 in the air on smoggy day. A light beam at a wavelength of 450 nm was reflected off a mirror on the roof Simpson Tower back to a UV/vis absorption spectrometer on Physical Sciences. The total pathlength traversed by the light was 335m. An absorbance of A= 0.0276 was measured. If the absorption coefficient of NO_2 at 450 nm is 450 is epsilon45nm = 2.97 times 10^4 L mol^-1 M^-1, determine the concentration of NO_2in the air.

Explanation / Answer

Absorbance = molar absorptivity x concentration x path length

with,

absorbance = 0.0276

path length = 335 m

molar absortivity = 2.97 x 10^4 L.mol-1.m-1

We get,

concentration of NO2 in air = 0.0276/2.97 x 10^4 x 335 = 2.774 x 10^-9 mol/L

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