Absorption Spectra: Determine Dilute/Thick Solutions

In summary, the conversation discussed the use of a graph of absorption coefficient versus wavelength to determine if a solution is optically dilute or optically thick. The higher the absorption coefficient, the more light is being absorbed, making the substance optically dilute. The equation for absorption coefficient was also mentioned, with a higher value indicating a thicker substance. Some sample values were provided as a reference.
  • #1
benndamann33
22
0
If you're reading a graph of absorption coefficient(cm^-1) versus wavelength(nm), how can you dtermine if the solution is optically dilute? What about optically thick? Thanks
Ben
 
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  • #2
Well as the absorbtion coefficient is per cm, i am guessing the higher it is the more light is being absorbed when traveling through a cm of the substance. So the optically diluter substance is probably the one with the lower coefficient.
 
  • #3
I agree, unfortunately I'm not comparing two spectra, but rather just answering for a variety of spectra is the solution optically dilute? Is it Optically thick? And not sure where the cut off is, can't find a value anywhere
 
  • #4
K i looked on wikipedia and the equation for absorbtion coefficient is:

I = Io e^-ax

Where I is transmitted intensity, Io is incident intensity, a is the attenuation coefficient and x is the thickness of the substance. Rearranging for a:

a = ln(Io/I)

If we try some values:

When 75% of light is transmitted a = 0.28

When 50% of light is transmitted a = 0.69

When 25% of light is transmitted a = 1.39

Maybe that will help you
 

1. What is an absorption spectrum?

An absorption spectrum is a graphical representation of the amount of light absorbed by a substance at different wavelengths. It is created by passing light through a sample and measuring the intensity of light that passes through the sample at different wavelengths.

2. How is the absorption spectrum of a substance determined?

The absorption spectrum of a substance is determined by using a spectrophotometer, which measures the amount of light transmitted through a sample at different wavelengths. The data collected is then plotted on a graph to create the absorption spectrum.

3. What is the difference between dilute and thick solutions in absorption spectroscopy?

Dilute solutions have a lower concentration of the substance being analyzed, while thick solutions have a higher concentration. In absorption spectroscopy, thicker solutions will absorb more light than dilute solutions, resulting in a higher absorbance value.

4. How does the concentration of a solution affect its absorption spectrum?

The concentration of a solution directly affects its absorption spectrum. As the concentration increases, the absorbance also increases. This is because a higher concentration of a substance will result in more molecules absorbing light at a given wavelength.

5. What are some potential applications of absorption spectroscopy?

Absorption spectroscopy has many applications in scientific research and industry. It is commonly used in pharmaceuticals, environmental testing, and food and beverage analysis. It can also be used to determine the concentration of a substance in a solution and to identify unknown substances by comparing their absorption spectra to known substances.

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