Podcast
Questions and Answers
The Beer-Lambert Law states that absorbance is inversely proportional to concentration, for a given wavelength and solution thickness.
The Beer-Lambert Law states that absorbance is inversely proportional to concentration, for a given wavelength and solution thickness.
False (B)
The proportionality constant 'k' in the Beer-Lambert Law equation (A = kC) is dependent on both the wavelength and the path length of the light beam through the solution.
The proportionality constant 'k' in the Beer-Lambert Law equation (A = kC) is dependent on both the wavelength and the path length of the light beam through the solution.
True (A)
Spectrophotometry is a technique that measures the transmittance of a solution at a specific wavelength.
Spectrophotometry is a technique that measures the transmittance of a solution at a specific wavelength.
False (B)
The absorbance spectrum of a chemical species is a plot of absorbance against concentration.
The absorbance spectrum of a chemical species is a plot of absorbance against concentration.
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A calibration curve is constructed by measuring the absorbance of solutions of known concentrations at different wavelengths.
A calibration curve is constructed by measuring the absorbance of solutions of known concentrations at different wavelengths.
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The slope of a calibration curve is equal to the molar absorption coefficient (epsilon).
The slope of a calibration curve is equal to the molar absorption coefficient (epsilon).
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To determine the concentration of an unknown solution using a calibration curve, one must measure its absorbance at the same wavelength used to create the calibration curve.
To determine the concentration of an unknown solution using a calibration curve, one must measure its absorbance at the same wavelength used to create the calibration curve.
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If the absorbance of an unknown solution falls outside the range of the calibration curve, the concentration can be determined by extrapolating the calibration curve.
If the absorbance of an unknown solution falls outside the range of the calibration curve, the concentration can be determined by extrapolating the calibration curve.
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Flashcards
Beer-Lambert Law
Beer-Lambert Law
Relates color of solution to concentration of colored species.
Absorbance (A)
Absorbance (A)
Measure of how much light a solution absorbs.
Proportionality constant (k)
Proportionality constant (k)
Constant linking absorbance to concentration, calculated by k = εl.
Molar Absorption Coefficient (ε)
Molar Absorption Coefficient (ε)
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Path Length (l)
Path Length (l)
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Spectrophotometry
Spectrophotometry
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Calibration Curve
Calibration Curve
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Determining Concentration
Determining Concentration
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Study Notes
Beer-Lambert Law
- The Beer-Lambert Law relates the color of a solution to the concentration of the colored chemical species.
- The absorbance of a solution is proportional to the concentration of the chemical species for a given wavelength and solution thickness.
- The relationship between absorbance (A) and concentration (C) is expressed as: A = kC where ‘k’ is the proportionality constant.
- 'k' is equal to the product of the molar absorption coefficient (ε) and the path length (l).
- Molar absorption coefficient is dependent on the wavelength, the nature of the solute and the solvent.
- Path length is the length of the solution traversed, i.e., the length of the cuvette used in the spectrophotometer.
- The absorbance is proportional to the concentration for a fixed wavelength and cuvette thickness.
Spectrophotometry
- Spectrophotometry is a technique used to measure the absorbance of a solution.
- It uses a spectrophotometer to measure the absorbance at a specific wavelength.
- The absorbance of a solution is measured at the wavelength where the absorption spectrum of the chemical species has maximum absorbance.
Calibration Curve
- A calibration curve is a graph that plots the absorbance of a solution against its concentration.
- The calibration curve is obtained by measuring the absorbance of solutions of different concentrations.
- The calibration curve is a straight line that passes through the origin.
- The slope of the calibration curve is equal to the proportionality constant ‘k’.
- The calibration curve can be used to determine the concentration of an unknown solution.
Determining Concentration
- The concentration of an unknown solution can be determined by measuring its absorbance and using the calibration curve.
- The absorbance of the unknown solution can be read from the calibration curve to determine the corresponding concentration.
- If the absorbance cannot be read directly from the calibration curve, then the concentration can be calculated using the Beer-Lambert Law (A = εcl).
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Description
Explore the Beer-Lambert Law, which explains the relationship between the absorbance of a colored solution and the concentration of its chemical species. Delve into key concepts such as molar absorption coefficient and path length, and learn how spectrophotometry is used to measure absorbance accurately.
