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FDSN 507 Midterm 2
Spectroscopy
Define spectroscopy. | The study of the interaction between electromagnetic radiation and matter; measure different wavelengths of light. |
What three things does spectroscopy include? | Absorption, emission, diffraction |
Name four different kinds of spectroscopy. | IR, UV-Vis, Fluorescence, NMR |
T or F: Light have wave-like properties. | True |
_____ represents the distance between successive maxima on any given wave. | Wavelength |
_____ is the number of occurances of a repeated event per unit time. | Frequency |
_____ is the magnitude of the electric vector at the wave maxima. | Amplitude |
Oscillating _____ and _____ fields make up a wave. | electric, magnetic |
A wave consists of discrete packets f energy called _____. | photons |
The energy of a photon can be defined in terms of ____ of the wave. | frequency |
_____ light is electromagnetic radiation composed of waves having a single frequency and wavelength. | Monochromatic |
T or F: Monochromatic light is obtained by refraction. | False |
Emitted light has longer _____ and less ____ than absorbed light. | wavelength, energy |
T or F: Atoms and molecules exist primarily in their excited state. | False |
T or F: The internal energy constant of a molecule is discrete. | True |
The relative _____ of an atom corresponds to the energy difference between excited and ground state. | potential energy |
The ____ range results in transitions between electronic energy levels. | UV-Vis |
The ____ range results in transitions between vibrational energy levels. | IR |
Describe the steps in absorption. | 1. Energy from electromagnetic radiation is transferred to an atom. 2. Atom goes from ground to excited state. 3. Absorption spectrum is obtained. |
Name two ways which a molecule may dissipate energy. | Heat, emission of radiation |
What are the two types of UV-Vis spectroscopy? Which is qualitative and which is quantitative? | Absorbance (qualitative), fluorescence (quantitative) |
____ spectroscopy is based on the amount of light absorbed from a reference beam as it passes through a sample solution. | Absorbance |
T or F: Analyte present in solution will not affect the amount of light transmitted. | False |
Relative transmittance and absorption are correlated to analyte _____. | concentration |
T or F: Absorbance is linear with concentration, transmittance is not. | True |
____ law gives the relationship between absorbance and concentration. | Beer's |
Define zeroing. | A reference cell is used to correct for loss due to scattering and reflection. |
What three conditions might cause deviations from Beer's law? | Analyte concentration is > 10 mM, chemical processingcause dissociation of molecules, polychromatic light causes different absorptivity. |
Quartz and fused silica holding cells are used for ____ spectroscopy. | UV |
Silicate plates and plastic cells are used for ___ spectroscopy. | Vis |
What should be considered procedurally for spectroscopy? | Sample prep, selection of appropriate wavelength, calibration of the instrument. |
T or F: A linear calibration curve obeys Beer's law. | True |
Why might a calibration curve be non linear? | Absorbance per change in concentration is not constant, limitations in instrument. |
Calibration of UV-Vis requires a _____ protocol. | standard addition |
T or F: High relative errors result with measurements of intermediate transmittance. | False |
Describe fluorescence spectroscopy. | The signal measured is the electromagnetic radiation emitted from the analyte. |
T or F: The optimum radiation wavelength for fluorescence spectroscopy is during excitation and a shorter wavelength during emission. | False |