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Beer-Lambert Law:
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The molar absorptivity coefficient (ε) is a measure of how strongly a chemical species absorbs light at a particular wavelength. It is a fundamental property in spectrophotometry and is used to quantify the concentration of substances in solution using the Beer-Lambert law.
The calculator uses the Beer-Lambert law:
Where:
Explanation: The Beer-Lambert law states that absorbance is directly proportional to the concentration of the absorbing species and the path length of light through the solution.
Details: Molar absorptivity is crucial in analytical chemistry for determining unknown concentrations, characterizing compounds, and validating analytical 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 chromophores. Most organic compounds have ε values between 1,000 and 50,000 L/mol-cm.
Q2: How does wavelength affect molar absorptivity?
A: Molar absorptivity is wavelength-dependent. Each compound has maximum absorption at specific wavelengths, where ε is highest.
Q3: What are the limitations of the Beer-Lambert law?
A: The law assumes monochromatic light, dilute solutions, and no chemical interactions. Deviations occur at high concentrations or with scattering solutions.
Q4: How is molar absorptivity determined experimentally?
A: By measuring absorbance at known concentrations and path lengths, then calculating ε from the slope of the absorbance vs. concentration plot.
Q5: Why is molar absorptivity important in quantitative analysis?
A: It allows calculation of unknown concentrations from absorbance measurements, making it fundamental in UV-Vis spectrophotometry for analytical applications.