Questions and Answers
What is the function of a spectrometer?
The instrument counts the number of photons hitting the detector in a specific period of time.
Absorption is proportional to what?
The absorbance (A) at a given λ is proportional to the concentration of the absorbing species (C).
State the Beer Lambert Law.
Absorbance = Molar Absorptivity * Path Length * Concentration
What happens to the absorbance when the size of the cuvette is adjusted?
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How does the color of the solution relate to the color of λmax?
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What is the difference between parallel and serial dilutions?
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How does the concentration of the 4th dilution using parallel dilutions compare to the concentration of the 4th dilution using serial dilutions?
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How would an error in the first dilution of each type affect the 4th dilution?
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Calculate the diluted concentration if you have a 5.25 x 10^-4 M stock solution and mix a 3.00 mL aliquot with 2.00 mL of diluent.
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What does the perceived color of objects depend on?
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Study Notes
Spectrometer Function
- A spectrometer counts the number of photons reaching the detector within a specific timeframe.
Absorption Proportionality
- Absorbance (A) correlates with the concentration (C) of the absorbing species in many materials.
Beer Lambert Law
- Formula: Absorbance = Molar Absorptivity × Path Length × Concentration.
Cuvette Size Impact on Absorbance
- Enlarging the cuvette increases absorbance, while reducing its size decreases absorbance.
Color Relationship with λmax
- The solution's color is typically complementary to the wavelength color based on the color wheel.
Types of Dilutions
- Dilutions can be arranged in two ways: serial dilutions (stepwise) or parallel dilutions (side by side).
- Primary goal is to achieve specific concentrations from a single known "stock" solution.
Concentration Comparison of Dilutions
- The 4th dilution in parallel is at 11% stock, while in serial it is at 0.01% stock.
- Serial dilutions have a narrower concentration range (0.01% to 10%) compared to parallel dilutions (11% to 78%).
- Serial dilutions allow for lower concentrations and have larger room for error.
Error Impact on Dilutions
- An error in the serial dilution affects subsequent dilutions, making the 4th dilution incorrect.
- An error in parallel dilution does not affect subsequent dilutions as each is independent.
Calculation of Diluted Concentration
- For a 5.25 x 10⁻⁴ M stock solution diluted with water:
- Using M1V1 = M2V2, diluted concentration is 3.15 x 10⁻⁴ M.
Perceived Color of Objects
- Object color is determined by how light interacts with electrons in molecules or atoms.
- The absorbed wavelengths dictate the perceived color, which is influenced by the object's molecular structure.
- The perception of color starts with light absorption by molecules in the observer's eye, leading to the transmission or reflection of particular wavelengths.
- A blue object absorbs other wavelengths, reflecting or transmitting blue light to the observer.
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Description
Test your knowledge on absorption spectra with these flashcards! Learn about spectrometer functions, the Beer-Lambert Law, and the relationship between absorbance and concentration. Perfect for students studying chemistry and physics.