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Questions and Answers
What is the Beer-Lambert Law?
The Beer-Lambert Law states that there is a linear relationship between the absorbance and the concentration of a solution.
What does the molar absorption coefficient (ᵋ) measure?
It measures how strong an absorber the sample is at a particular wavelength of light.
What is the typical length of the cuvette used for absorbance measurement?
1 cm
What is transmittance?
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The formula for absorbance is A = log /
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Absorbance has a linear relationship with transmittance.
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Which of the following conditions can deviate from Beer’s Law? (Select all that apply)
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How is absorbance (A) related to transmittance (%T)?
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Study Notes
Beer-Lambert Law
- A linear relationship between absorbance and concentration, molar absorption coefficient, and optical path length of a solution.
- Molar absorption coefficient (ε) is a measure of how strongly a sample absorbs light at a specific wavelength.
- Concentration (C) is the molarity (moles per liter) of the sample dissolved in the solution.
- Path length (l) is the distance light travels through the solution, typically 1 cm in a cuvette.
Application of Beer-Lambert Law
- Spectrophotometers use this law to determine the concentration of a solution by measuring its absorbance.
- The relationship between absorbance and concentration is linear only within a certain range, requiring calibration to determine the linearity limits.
- Spectrophotometric calculations compare the absorbance of an unknown sample to a standard of known concentration.
- Au/As= Cu/Cs, where A is absorbance, C is concentration, u is the unknown, and s is the standard.
Transmittance
- The ratio of transmitted light to incident light is called transmittance.
- Transmittance is often expressed as a percentage: T% = 100 x It / Io, where It is transmitted light and Io is incident light.
- Absorbance (A) is related to transmittance through the formula: A= log 100/ % T
- Absorbance is inversely proportional to transmittance.
Conditions that Deviate from Beer's Law
- Elevated concentration of the analyte can exceed the reagent's reaction capacity.
- The light source might not be perfectly monochromatic.
- The solvent can absorb light interfering with the measurement.
- Stray light can falsely increase the measured absorbance.
- Cuvette imperfections can cause variations in light path length.
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Description
Explore the Beer-Lambert Law, a fundamental principle in analytical chemistry that describes the relationship between absorbance and concentration of solutions. Understand how this law is applied in spectrophotometry to determine the concentration of unknown samples. Dive into the concepts of molar absorption coefficient and optical path length for deeper insights.
