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Questions and Answers
What is Beer-Lambert Law?
A linear relationship between absorbance and concentration.
The molar absorption coefficient (ᵋ) is a sample dependent property and is a measure of how strong an absorber the sample is at a _______ of light.
particular wavelength
What does C represent in Beer-Lambert Law?
Concentration in moles per liter (M).
What is the typical length of the cuvette used for absorbance measurement?
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The Beer-Lambert law is applicable for all concentrations without deviation.
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What is the formula relating absorbance (A) to concentrations (Cu and Cs)?
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Transmittance is defined as the ratio of the amount of _______ light to the amount of incident light.
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What is the relationship between absorbance (A) and percent transmittance (%T)?
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Which of the following conditions can deviate from Beer’s law? (Select all that apply)
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Study Notes
Beer-Lambert Law
- Relates absorbance to concentration, molar absorption coefficient, and optical path length.
- Linear relationship between absorbance and concentration.
- Molar absorption coefficient (ε) is a sample-dependent property that measures how strongly a sample absorbs at a specific wavelength.
Spectrophotometers
- Spectrophotometers use Beer-Lambert Law to measure the concentration of a solution.
- There is a limited linear response between absorbance and concentration.
- This linearity is dependent on the concentration of the analyte.
Spectrophotometric Calculation
- The absorbance of an unknown concentration is compared to a standard solution of a known concentration.
- The ratio of absorbances is equal to the corresponding ratio of concentrations: Au/AS = Cu/Cs
- Where 'A' represents absorbance, 'C' represents concentration, 'u' stands for unknown, and 's' stands for standard.
Transmittance
- Transmittance is the ratio of transmitted light to incident light.
- It is also expressed as a percentage: T% = 100 x It / Io.
Absorbance and Transmittance Relationship
- Absorbance (A) is related to transmittance (T) through the equation: A = log (1/T)
- A = 2.00 – log %T.
- Absorbance has a logarithmic relationship with transmittance, where an absorbance of 0 corresponds to 100% transmittance.
Conditions that Deviate from Beer's Law
- Elevated Concentration: High analyte concentration can exceed the reagent's reaction capacity, leading to deviation from linearity.
- Non-monochromatic Light: Using light that is not a single wavelength can cause deviations.
- Solvent Interference: Absorbance caused by the solvent can affect accuracy.
- Stray Light: Light that enters the detector outside of the desired path can lead to errors.
- Cuvette Imperfections: Scratches or imperfections in the cuvette can affect the light path and measurement.
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Description
Explore the Beer-Lambert Law and its application in spectrophotometry. This quiz covers the relationship between absorbance and concentration, the principles of spectrophotometric calculations, and the importance of transmittance in measuring solutions. Test your knowledge on the key concepts of this fundamental analytical tool.
