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Beer's Law Equation:
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Molar absorptivity (ε), also known as the molar extinction coefficient, is a measure of how strongly a chemical species absorbs light at a given wavelength. It is a fundamental constant in spectroscopy that characterizes the absorption properties of a substance.
The calculator uses Beer's Law equation:
Where:
Explanation: This equation describes the linear relationship between absorbance and concentration for a given substance and path length at a specific wavelength.
Details: Molar absorptivity is crucial in quantitative analysis, chemical identification, and determining unknown concentrations in spectrophotometric methods. It is specific to each compound and wavelength.
Tips: Enter absorbance (unitless), concentration in mol/L, and path length in cm. All values must be positive numbers. Ensure measurements are taken at the same wavelength for accurate results.
Q1: What are typical values for molar absorptivity?
A: Values range from near zero for weak absorbers to over 100,000 L/mol·cm for strong absorbers. Most organic compounds fall between 1,000-50,000 L/mol·cm.
Q2: Does molar absorptivity depend on wavelength?
A: Yes, molar absorptivity is wavelength-dependent and is typically reported at the wavelength of maximum absorption (λmax).
Q3: What factors affect molar absorptivity?
A: Temperature, solvent, pH, and the chemical structure of the absorbing species can all influence molar absorptivity values.
Q4: How is this different from absorption coefficient?
A: Molar absorptivity refers to molar concentration, while absorption coefficient may refer to mass concentration. Always check units carefully.
Q5: When is Beer's Law valid?
A: Beer's Law is valid for dilute solutions where there is no chemical interaction between absorbing species and the absorbance is linear with concentration.