When measuring absorbance of a solution using a colorimeter, at which wavelength should the colorimeter be set?

• A. At the wavelength where the solution transmits light most strongly (maximum transmittance)
• B. At any random wavelength within the visible spectrum
• C. At the wavelength where the solution absorbs light most strongly (maximum absorbance)
• D. At the wavelength corresponding to the color of the solution

Answer: (C)

Verified step by step guidance

1. Understand that absorbance and transmittance are related properties describing how a solution interacts with light. Absorbance measures how much light is absorbed, while transmittance measures how much light passes through the solution.
2. Recall that the colorimeter is used to measure the absorbance of a solution, which is directly related to the concentration of the absorbing species according to Beer's Law.
3. Identify that to get the most sensitive and accurate absorbance measurement, the colorimeter should be set to the wavelength where the solution absorbs light most strongly, i.e., where absorbance is at its maximum.
4. Recognize that measuring at the wavelength of maximum absorbance ensures the greatest difference in absorbance for changes in concentration, improving the precision of the analysis.
5. Note that setting the colorimeter at the wavelength of maximum transmittance or at a random wavelength would result in lower absorbance readings and less reliable data, and that the wavelength corresponding to the color of the solution is typically the complementary color to the absorption maximum, not the absorption maximum itself.