Question

a student measures the absorbance of a solution containing fescn²⁺ ions 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 fescn²⁺ be affected if the student incorrectly orients the cuvette so that the path of the light is through the frosted sides of the cuvette?
a the measured absorbance of the fescn²⁺ solution will not be affected.
b the measured absorbance of the fescn²⁺ solution will be higher than the actual absorbance.
c the measured absorbance of the fescn²⁺ solution will be lower than the actual absorbance.
d the effect on the measured absorbance of the fescn²⁺ solution depends on the concentration of the fescn²⁺ solution.

Explanation:

Frosted walls scatter light. When light passes through frosted walls instead of transparent ones in a spectrophotometry experiment, less light reaches the detector. According to the Beer - Lambert law ($A = \epsilon lc$, where $A$ is absorbance, $\epsilon$ is the molar absorptivity, $l$ is the path - length, and $c$ is the concentration), the instrument measures a lower transmittance and calculates a higher absorbance value than the actual absorbance of the solution.

Answer:

B. The measured absorbance of the $\text{FeSCN}^{2 + }$ solution will be higher than the actual absorbance.