Final answer:
A cuvette of ethanol is needed for the colorimeter to measure absorbance. The colorimeter uses the cuvette filled with ethanol as a blank reference to accurately measure the concentration of a substance in a solution.
Step-by-step explanation:
A cuvette of ethanol is needed for the colorimeter to measure absorbance.
The colorimeter is an instrument used for measuring the amount of light absorbed by a sample.
By using a cuvette filled with ethanol as a blank reference, the colorimeter can measure the absorbance of other solutions by comparing the light transmitted through them relative to the blank.
This allows for accurate measurements of the concentration of a substance in a solution.