Question

A student measures the absorbance of a solution containing FeSON on using a spectrophotometer. The cuvette used by the student has two frosted walls and two transparent walls. The student properly orients the cuvette so that the path of the light goes through the transparent sides of the cuvette when calibrating the spectrophotometer. How will the measured absorbance of the FeSCN be affected if the student incorrectly orients the cuvette so that the path of the light is through the frosted sides of the cuvette? The measured absorbance of the F.SCN' solution will not be affected The measured absorbance of the FeSCN solution will be higher than the actual absorbance The measured absorbance of the FeSCN' solution will be lower than the actual absorbance. D) The effect on the measured absorbance of the FeSCN+ solution depends on the concentration of the FeSCN solution

Answer 1

The answer would be B. The measured absorbance of the FeSCN2+ solution will be higher than the actual absorbance. Some of the light will be scattered/reflected by the frosted surfaces of the cuvette; thus less light will reach the detector in the spectrophotometer, making it appear as if the sample had absorbed more light.

Answer 2

we know from Lambert Beer Law

absorbance A= molar absorptivity co efficient * concentration * length of the path

also A= log (intensity of light incident I₀/intensity of light leaving I)

A=log (I_o/I)

if lesser amount of light is absorbed then lesser will be the absorbance

The frosted sides is translucent in nature so does allow light to completely pass through it

if the student orient the frosted side of the cuvette in direction of the path of light,,as the amount entering the cuvette will be less as frosted sides is translucent in nature ,thus the interaction will be less, so , thus absorbance will be less as absorbance is directly proportional to amount of light incident on the cuvette

so the absorbance of the solution will be lesser than the actual absorbance (option C)