Question

Annotatic A student measures the absorbance of a solution containing FeSCN ion 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 FeSCN 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. The effect on the measured absorbance of the FeSCN D solution depends on the concentration of the FeSCN solution

Answer 1

Firstly, frosted sides are present in a cuvette to prevent scattering of light from the side of the cuvette. Some of th samples are cloudy and tend to scatter light which give incorrect readings. Hence, frosted sides tend to prevent the scattering to give as accurate results as possible. However, black walled cuvettes are far more accurate than frosted cuvettes.

From the condition stated above, option (B) looks most appropriate. The transparent side of the cuvette used while calibration to obtain a baseline. Now, when the iron thiocyanate solution is subjected to spectrophotometer with light passing from the frosted side of the cuvette the absorbance will increase the pattern will be something as shown in the figure attached below :

​​​​​​The absorbance of solution will be higher and the baseline will also shift upwards. This can be explained by the rough sides of the frosted walls of the cuvette, which causes the overall absorbance of the solution higher than what could have been if the experiment was performed with the smooth sides.

fes CN Solution, Salvent