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Chapter 16: Problem 12

Define absorption, absorbance, percent transmittance, and transmittance.

Short Answer

Expert verified
Absorption converts light to energy; absorbance measures light absorbed; transmittance measures light passing through; percent transmittance is transmittance as a percentage.

Step by step solution

01

Understanding Absorption

Absorption is the process by which a material, substance, or object takes in light and converts it into other forms of energy, often leading to an increase in temperature. In the context of spectroscopy, absorption refers to the reduction in intensity of light as it passes through a medium.
02

Define Absorbance

Absorbance, often denoted as 'A', is a measure of the amount of light absorbed by a solution. It is a dimensionless quantity that quantifies how much light is absorbed by the sample solution at a particular wavelength. The formula for absorbance is: \[ A = - ext{log}_{10} rac{I}{I_0} \] where \( I \) is the intensity of light that passes through the sample and \( I_0 \) is the initial intensity of light.
03

Define Transmittance

Transmittance, often denoted as 'T', is the fraction of light that passes through a sample. It is calculated as the ratio of the intensity of light passing through the sample \( I \) to the intensity of light that initially strikes the sample \( I_0 \). The formula for transmittance is: \[ T = rac{I}{I_0} \] Transmittance is usually expressed as a percentage.
04

Define Percent Transmittance

Percent transmittance is the transmittance expressed as a percentage. It indicates how much light is transmitted through a solution relative to the original intensity. The formula to convert transmittance into percent transmittance is: \[ ext{Percent Transmittance (%T)} = T imes 100 \] where \( T \) is the transmittance.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Absorption
In the realm of spectroscopy, absorption refers to the process by which a material interacts with light. When light encounters a substance, some of that light can be absorbed. The light energy is taken in by the atoms or molecules of the material, often converting it to other forms of energy such as heat. Absorption directly affects the intensity of light passing through a material. It determines how much light will continue through as opposed to how much will be reduced or blocked.
  • Absorption is crucial for understanding how substances interact with light.
  • Substances absorb different wavelengths of light based on their properties.
  • Increased absorption can lead to a rise in temperature as energy is converted.
By understanding absorption, we can determine the properties and composition of different materials such as pollutants or chemicals in a solution.
Absorbance
Absorbance measures how much light a material or solution absorbs. It is represented by 'A' and is a dimensionless number. Unlike absorption, which is a process, absorbance quantifies that process.The formula for absorbance is:\[ A = -\log_{10} \frac{I}{I_0} \]where:- \( I \) is the intensity of the light that passes through the substance.- \( I_0 \) is the original light intensity before encountering the substance.Absorbance allows us to quantify the interaction of light with a material clearly. This is especially useful in laboratory settings to deduce the concentration of substances within a solution by comparing measured absorbance with known standards.
  • High absorbance indicates less light passing through.
  • Absorbance has no units, making it suitable for direct comparative analysis.
  • It's essential in determining material concentrations.
Transmittance
Transmittance describes how much light successfully passes through a sample, escaping the effects of absorption. It is a key factor in determining how transparent or opaque a material is.The formula for transmittance is:\[ T = \frac{I}{I_0} \]where:- \( I \) is the light intensity after passing through the sample.- \( I_0 \) is the initial light intensity before hitting the sample.Transmittance is often expressed as a ratio, but it can be multiplied by 100 to yield a percentage. The greater the transmittance, the more light that moves through a sample without being absorbed.
  • Transmittance is essential in contexts where transparency of materials needs assessment.
  • High transmittance implies low absorption, indicating clearer materials.
  • It's crucial for applications such as determining the clarity of liquids or glasses.
Percent Transmittance
Percent transmittance (%T) is a clear way to express transmittance relative to the initial light entering a sample. It offers a straightforward percentage that is easy to understand and visualize.To calculate percent transmittance:\[ \text{Percent Transmittance (%T)} = T \times 100 \]This conversion allows one to easily see the proportion of light that transmits through a material compared to the original amount.
  • Percent transmittance helps in easily communicating results in practical settings.
  • It is an intuitive method for expressing how much of the light was transmitted.
  • Useful in fields from art restoration to environmental testing.

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Most popular questions from this chapter

Discuss the effect of the slit width on the resolution of a spectrophotometer and the adherence to Beer's law. Compare it with the spectral slit width.

Titanium is reacted with hydrogen peroxide in \(1 M\) sulfuric acid to form a colored complex. If a \(2.00 \times 10^{-5} M\) solution absorbs \(31.5 \%\) of the radiation at \(415 \mathrm{nm}\), what would be (a) the absorbance and (b) the transmittance and percent absorption for a \(6.00 \times 10^{-5} M\) solution?

The core of a simple single-cavity bandpass-type interference filter consists of a thin layer of a dielectric material with thin reflective metal layers on each face. Only the wavelength \(\lambda\) that meets the constructive interference criterion $$ n \lambda=2 t n $$ is transmitted, where \(n\) is the order of interference, and \(t\) and \(n\) are, respectively, the thickness and the refractive index of the dielectric layer, and light is incident perpendicularly on the filter. For a core dielectric of 200 -nm thickness and a refractive index of \(1.377,\) what is the transmitted wavelength through this filter if the emission from a white LED (Figure 16.13 ) is focused on it?

Define absorptivity and molar absorptivity.

An analyst would like to measure the concentrations of benzene in ethanol with a spectrophotometer using \(1-\mathrm{cm}\) pathlength cells. Benzene has two characteristic absorption wavelengths at \(204 \mathrm{nm}\) and \(256 \mathrm{nm},\) and ethanol has a minimum usable (cutoff) wavelength at \(220 \mathrm{nm}\). (a) Which absorption wavelength of benzene should be used for the analysis? (b) Which kinds of light source would be ideal for this measurement? (c) What cell material would be used in the spectrophotometer for this analysis?
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