Question

(10 pts total) You are going to collect UV-Vis spectra of an unknown solution of beta carotene (structure given below) dissolved in hexane. a. (5 pts) You have a choice between a quartz cuvette or a Thallium Bromoiodide (KRS-5) cuvette? Which should you choose and why? The following chart may be useful. KRISTIILTH 100 30000 1000 3000 Wavelength, 0 1000 b. (5 pts) How would taking the spectrum in ethanol affect your spectrum? Explain.

Answer 1

Part a: I have to select a cuvette which must be made of a material that do not absorb the same ray light the solute absorbs. Looking at the UV-Vis spectrum, the carotene almost absorbs at 420nm and at 476nm. This waves are absorbed also by quartz cuvette because it absorbs waves whose longitudes shorter than 3750nm. Nonetheless, the KRS-5 cuvette does not absorb in UV-Vis spectrum because absorbs at IR spectrum from 700nm to upper long waves longitudes. If I use a cuvette that absorbs the same wave that the analyte, it increases the absorbance by modifying the absorptivity and path length.

Part b: The ethanol absorbs at 445nm to 450nm depending on its concentration. This increases the absorbance of the sample by other compound nor analyte.