Question

A student uses a spectrophotometer to analyze a solution of blue food dye. The student first rinses a cuvette with distilled water. Then the student adds the blue dye solution to the cuvette, forgetting to rinse the cuvette with the blue dye solution first. The student places the cuvette in the spectrophotometer and measures the absorbance of the solution. Assuming that some distilled water droplets were still in the cuvette when the blue dye solution was added, how would the measured absorbance be affected?

Answer 1

Answer and Explanation:

The measured absorbance will be lower than the real absorbance of the dye solution. The water droplets will dilute the solution, thus the concentration of the dye in the cuvette will be lower than the real concentration. Notice that a cuvette has a volume of approximately 1-2 mL, so a few droplets are significant in volume change. If you have water droplets before you place the solution in the cuvette, the solution will be more diluted (you will have less dye molecules per volume than in the real-not diluted-solution).