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Questions and Answers
A scientist is using a spectrophotometer to analyze a sample. Which of the following principles is directly related to the linear relationship between absorbance and concentration, assuming the pathlength and molar extinction coefficient are constant?
A scientist is using a spectrophotometer to analyze a sample. Which of the following principles is directly related to the linear relationship between absorbance and concentration, assuming the pathlength and molar extinction coefficient are constant?
- Quantum entanglement
- Beer's Law (correct)
- The principle of fluorescence
- Lambert's Law
In UV-Vis spectroscopy, what is the significance of the molar extinction coefficient (E) in the Beer-Lambert Law ($A = Ecb$)?
In UV-Vis spectroscopy, what is the significance of the molar extinction coefficient (E) in the Beer-Lambert Law ($A = Ecb$)?
- It corrects for pathlength variations.
- It accounts for variations in the concentration of the solvent.
- It quantifies the amount of light scattered by the sample.
- It represents the absorptivity of a substance at a given wavelength. (correct)
Why is it important to prepare standard solutions with the same reagents and at the same time as the unknown samples when constructing a calibration curve for food analysis using UV-Vis spectroscopy?
Why is it important to prepare standard solutions with the same reagents and at the same time as the unknown samples when constructing a calibration curve for food analysis using UV-Vis spectroscopy?
- To ensure the instrument is properly calibrated.
- To increase the absorbance readings of the samples.
- To minimize the cost of reagents.
- To account for matrix effects and ensure consistent experimental conditions. (correct)
A researcher observes that a colored compound exhibits strong absorbance in both the UV and visible regions. What can be generally inferred about the electronic transitions within this compound?
A researcher observes that a colored compound exhibits strong absorbance in both the UV and visible regions. What can be generally inferred about the electronic transitions within this compound?
A scientist is using a UV-Vis Spectrophotometer to measure a substance. The range is between 220 - 780nm, What type of radiation are they using?
A scientist is using a UV-Vis Spectrophotometer to measure a substance. The range is between 220 - 780nm, What type of radiation are they using?
What fundamental property of electromagnetic radiation is measured in Hertz (Hz)?
What fundamental property of electromagnetic radiation is measured in Hertz (Hz)?
In spectroscopy, what constitutes a 'spectrum'?
In spectroscopy, what constitutes a 'spectrum'?
Which region of the electromagnetic spectrum is commonly utilized in food analysis laboratories for spectroscopic methods?
Which region of the electromagnetic spectrum is commonly utilized in food analysis laboratories for spectroscopic methods?
What is fundamentally measured in absorption spectroscopy?
What is fundamentally measured in absorption spectroscopy?
How does emission spectroscopy differ fundamentally from absorption spectroscopy?
How does emission spectroscopy differ fundamentally from absorption spectroscopy?
If a substance absorbs light in the visible region of the electromagnetic spectrum, what process is occurring at the molecular level?
If a substance absorbs light in the visible region of the electromagnetic spectrum, what process is occurring at the molecular level?
Which of the following best describes the relationship between wavelength and frequency of electromagnetic radiation?
Which of the following best describes the relationship between wavelength and frequency of electromagnetic radiation?
A molecule is exposed to electromagnetic radiation that causes its chemical bonds to vibrate. Which type of radiation is most likely responsible?
A molecule is exposed to electromagnetic radiation that causes its chemical bonds to vibrate. Which type of radiation is most likely responsible?
In UV-Vis spectroscopy, what range of the electromagnetic spectrum is utilized?
In UV-Vis spectroscopy, what range of the electromagnetic spectrum is utilized?
When a molecule transitions from a higher energy state to a lower energy state without emitting radiation, this process is known as:
When a molecule transitions from a higher energy state to a lower energy state without emitting radiation, this process is known as:
Which type of electromagnetic radiation is most likely to break chemical bonds when interacting with a molecule?
Which type of electromagnetic radiation is most likely to break chemical bonds when interacting with a molecule?
What is the relationship between wavelength and energy of a photon?
What is the relationship between wavelength and energy of a photon?
UV-Vis spectroscopy can be used to determine which of the following?
UV-Vis spectroscopy can be used to determine which of the following?
Compared to optical photons, X-ray photons are:
Compared to optical photons, X-ray photons are:
A scientist is using a spectrometer that emits radiation with wavelengths longer than 780 nm. What type of radiation is this?
A scientist is using a spectrometer that emits radiation with wavelengths longer than 780 nm. What type of radiation is this?
What is the primary effect of microwave radiation on chemical bonds?
What is the primary effect of microwave radiation on chemical bonds?
Which of the following applications primarily uses high-energy radiation such as X-rays or γ-rays?
Which of the following applications primarily uses high-energy radiation such as X-rays or γ-rays?
Flashcards
Spectroscopy
Spectroscopy
Study of molecular or atomic structure through spectrum measurement.
Electromagnetic Radiation
Electromagnetic Radiation
Energy that travels as electrical and magnetic waves in photons.
Frequency (v)
Frequency (v)
Number of oscillations per second of the electrical field; measured in Hertz (Hz).
Wavelength (λ)
Wavelength (λ)
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Absorption Spectroscopy
Absorption Spectroscopy
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Emission Spectroscopy
Emission Spectroscopy
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Spectrum
Spectrum
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Nonradiative Decay
Nonradiative Decay
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Types of Light
Types of Light
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Photon
Photon
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Radio Waves
Radio Waves
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Optical Photons
Optical Photons
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X-ray Photons
X-ray Photons
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Energy and Molecule Interaction
Energy and Molecule Interaction
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UV/Visible Spectroscopy
UV/Visible Spectroscopy
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Wavelength of UV Radiation
Wavelength of UV Radiation
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Wavelength of Visible Radiation
Wavelength of Visible Radiation
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Spectrophotometer
Spectrophotometer
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UV Radiation
UV Radiation
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Beer-Lambert Law
Beer-Lambert Law
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Molar Extinction Coefficient (E)
Molar Extinction Coefficient (E)
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Calibration Curve
Calibration Curve
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Study Notes
Food Analysis (NUTR 210) Lecture 3
- Spectroscopy: The study of how matter interacts with light (or electromagnetic radiation).
- Electromagnetic Radiation: Energy that travels as both electric and magnetic waves in packets called photons.
- Frequency (v): The number of times an electrical field oscillates per second, measured in Hertz (Hz).
- Wavelength (λ): The distance between successive points on a wave, in the same phase.
- Electromagnetic Spectrum: A range of electromagnetic radiation, from gamma rays to radio waves, with increasing or decreasing frequency and energy. Each region has a different wavelength range. UV (220-380 nm), VISIBLE (380-780 nm), IR
- (Note: Table of wavelengths on page 3 details this)*
- Spectroscopy as Analytical Technique: Used to determine the structure and concentration of molecules in matter.
- Types of Spectroscopy:
- UV/Visible Spectroscopy: Identifies the concentration or presence of different substances and molecules in liquids or solutions (and some solids). -Uses UV or visible light. -Measures the absorption of light by the sample. -Instruments used are spectrophotometers or spectrometers. -UV-Vis spectroscopy works for substances with atoms containing functional groups that absorb UV and Visible radiation (e.g., Acetaldehyde, Acetone, Acetic acid, B-carotene, oxalic acid, phenol, etc.). -Infrared (IR) Spectroscopy: Identifies chemical compounds based on their vibrational energy states. -Measures the absorption of infrared light to identify chemical bonds, especially functional groups.
- Beer-Lambert Law: A fundamental law in spectrophotometry that shows the absorbance of a substance is directly proportional to the concentration (c) and path length (b) through the sample
- (Absorbance (A) = ε c b, and ε is molar extinction coefficient)*
- Calibration Curves: Used to determine analyte concentration from absorbance. Standards or known concentrations are used to establish the relationship.
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