Chapter 15, Problem 15.1YT

Interpretation Introduction

(a)

Interpretation:

Which scenario corresponds to a greater proportion of light absorbed by a given sample is to be determined.

Concept introduction:

In a typical UV–vis spectroscopy, a range of wavelengths (usually $\text{200–800}$ nm) is passed through the sample to analyze. At each wavelength, the intensity of light that reaches the detector (${\text{I}}_{\text{detected}}$) is measured, and it is compared with the initial intensity of light radiation from the source (${\text{I}}_{\text{source}}$). At certain wavelengths, the sample (analyte) might interact with the light, that is, the fraction of light is transmitted, absorbed, and scattered through the sample. The fraction of transmitted light is detected by the detector, in which case, ${\text{I}}_{\text{detected}}$ would be smaller than ${\text{I}}_{\text{source}}$. The percent transmittance (%T) is calculated according to this equation: ${\text{\%T = (I}}_{\text{detected}}{\text{/I}}_{\text{source}}\text{) × 100}$.

The percent transmittance is converted into the corresponding absorbance by using this equation: ${\text{A = - log(I}}_{\text{detected}}{\text{/I}}_{\text{source}}\text{) = 2 - log(\%T)}$. So more the transmittance, lesser will be the absorbance, and the transmitted light is detected by a detector. Absorbance is directly proportional to the light absorbed. Higher the absorbance, greater the portion of light absorbed by the sample.

Interpretation Introduction

(b)

Interpretation:

Which scenario corresponds to a greater proportion of light absorbed by a given sample is to be determined.

Concept introduction:

In a typical UV–vis spectroscopy, a range of wavelengths (usually $\text{200–800}$ nm) is passed through the sample to analyze. At each wavelength, the intensity of light that reaches the detector (${\text{I}}_{\text{detected}}$) is measured, and it is compared with the initial intensity of light radiation from the source (${\text{I}}_{\text{source}}$). At certain wavelengths, the sample (analyte) might interact with the light, that is, the fraction of light is transmitted, absorbed, and scattered through the sample. The fraction of transmitted light is detected by the detector, in which case, ${\text{I}}_{\text{detected}}$ would be smaller than ${\text{I}}_{\text{source}}$. The percent transmittance (%T) is calculated according to this equation: ${\text{\%T = (I}}_{\text{detected}}{\text{/I}}_{\text{source}}\text{) × 100}$.

The percent transmittance is converted into the corresponding absorbance by using this equation: ${\text{A = - log(I}}_{\text{detected}}{\text{/I}}_{\text{source}}\text{) = 2 - log(\%T)}$. So more the transmittance, lesser will be the absorbance, and the transmitted light is detected by a detector. Absorbance is directly proportional to the light absorbed. Higher the absorbance, greater the portion of light absorbed by the sample.