Multiple Choice
In UV-Vis spectrophotometry, absorbance is defined as , where transmittance is the fraction of light transmitted. Which expression correctly gives percent transmittance from absorbance ?
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17. Fundamentals of Spectrophotometry
Measuring Absorbance
Multiple Choice
Why is a specific wavelength of light chosen when recording absorbance measurements for a dye?
A
To minimize the amount of light absorbed by the solvent
B
To avoid interference from the cuvette material
C
To ensure the instrument uses the lowest possible energy light
D
To maximize sensitivity by measuring at the dye's absorbance maximum (λmax)
Verified step by step guidance1
Understand the concept of absorbance measurements: Absorbance is a measure of how much light a substance absorbs at a specific wavelength. It is governed by the Beer-Lambert law, which relates absorbance to the concentration of the absorbing species and the path length of the light through the sample.
Identify the importance of λmax: λmax is the wavelength at which a substance exhibits its maximum absorbance. This is the point where the dye absorbs the most light, making it the most sensitive wavelength for detecting changes in concentration.
Explain why λmax is chosen: By measuring absorbance at λmax, the sensitivity of the analysis is maximized. This ensures that even small changes in the dye's concentration result in noticeable changes in absorbance, improving the accuracy and reliability of the measurement.
Address the incorrect options: The other choices (minimizing light absorbed by the solvent, avoiding interference from the cuvette material, and using the lowest energy light) are not the primary reasons for selecting a specific wavelength. While these factors may be considered, they do not directly relate to maximizing sensitivity.
Conclude the reasoning: The correct answer is to maximize sensitivity by measuring at the dye's absorbance maximum (λmax), as this ensures the most accurate and sensitive detection of the dye's concentration.
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