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CHEM 2368

Spectroscopy

QuestionAnswer
What is spectroscopy? The study of how emr reacts with matter
What is chromatography? Separation of mixture components by passing through a stationary medium
What are four ways that light can react to matter? Absorb, emit, luminesce, scatter
What is emr? electromagnetic radiation
What does the symbol v stand for? frequency
What is the symbol for speed of light? c
What is the speed of light? 3x10^8
What is the formula for energy? E=hv=hc/wavelength
How does light behave? Acts like a particle and like a wave
What are the three properties of light's wave behavior? velocity/speed of light amplitude- the number of photons present or the intensity Period- the time for one oscillation
What is the relationship between frequency and wavelength? longer lengths have shorter frequencies.
What units does frequency have? Hertz, or metres per second
What are the regions of radiation? xray, UV, visible, IR, microwave, radio
When will a chemical absorb a wavelength? When the energies match
When will a chemical emit? When the chemical's energy is greater than the wavelength
What is refraction? The angle in which light passes through a medium
Differentiate between polychromatic light and monochromatic light? Polychromatic light has many wavelengths. Monochromatic light has one wavelength.
What causes interference? Wave like properties of light
What are the two types of interference? In phase/constructive and out of phase/destructive.
What is polarization? Light is forced onto one plane
What is scattering? The path of light is altered when passed through a medium
What are the three types of scattering? Rayleigh- particles smaller than wavelength Tyndall- light is scattered by visible haze Raman- molecular vibrations cause scattering
What happens to the electrons in absorbance via atomic spectrocopy? an electron is excited to the next level- the energy that is required will vary
What happens to the molecule in molecular spectroscopy? Different orbitals and bonds are excited to higher orbitals
What are the types of orbitals/bonds associated with molecules? sigma- occurs with all bonds pi- only occurs with multiple bonds non bond
From least energy needed to most energy needed, list the orbital excitations. non bonding to pi* non bonding to sigma* pi to pi* sigma to sigma*
What wavelengths exist in the visible spectrum? 380-750nm
What color has the shortest and longest wavelength? blue has shortest, red has longest
Three types of energy transitions from lowest energy to highest. Rotational, vibrational, electronic
What are the four types of emission? Emission, fluorescence, phosphorescence, chemilluminescence
Differentiate between fluorescence and phosphorescence? Fluorescence is rapid. phosphorescence is slow
What is a spectrum? Plot of light amplitude vs frequency/wavelength
What are the different spectra associated with atoms v. molecules? Atoms have line spectra. Molecules have band spectra.
What are the three types of molecular energy? Electronic, vibrational, and rotational.
When would lambda max not be used in analysis? 1. The sample is too concentrated 2. Something else in the sample absorbs that wavelength
What is Beer's Law? Absorbance is equal to the pathlength(cm) * molar concentration * absorptivity or molar absorptivity.
How are molar concentration and absorbance related? If pathlength and absorptivity are kept constant, then absorbance should equal concentration.
What is standard addition and why is it useful? Standard addition is when you add the same amount of the analyte to the samples in order to mitigate the interference.
What is the matrix of a solution? Everything but the analyte.
Does Beer's law work better for high or low concentrations? Low
Does Beer's Law apply to polychromatic or monochromatic light? Monochromatic- if polychromatic light is used, a monochrometer grating should be used.
What is stray radiation? Light that goes to the detector without going to the sample first.
What is dark current? Current which flows when there is no light. It causes absorbance to seem lower
Are instrumental deviations positive or negative? Negative.
In order, name the basic components of a spectrophototmeter. Source/lamp; entrance slit; collimating lens; diffraction grating; focusing slit; exit slit; sample; detector
What is the purpose of the entrance slit? Reduce stray radiation
What is the purpose of a collimating lens? Reduces stray radiation and improves refraction
Describe a reducing flame. A reducing flame has a high fuel to oxidant ratio, with a lower temperature, and lower ionization.
Describe an oxidizing flame. Low fuel to oxidant ratio, hot, refractory oxides may form.
Where is the hottest part of the flame? At the top of the interzonal region.
What are the parts of a flame? Primary combustion zone, interzonal region, and secondary combustion zone.
Summarize the processes that occur in a flame. Desolvation Volatization Dissociation Ionization
What happens during volatization? The aerosol is vaporized to molecules
What happens during dissociation? Neutral atoms are formed.
At which stage are band spectra produced? Volatization
What are some methods of sample introduction? Pneumatic nebulization via tubes Pneumatic nebulization bia crossflow
What are two types of spray chambers? Knock-out bead Sturman master
What are three instruments used for atomic absorption? Flame AA, ICP, and GFAAS
Does ICP use fuels and oxidants? What does it use. ICP uses Argon
What are two types of interference? Spectral and chemical
What is the best way to correct for spectral interference? Matrix match/standard addition
Give an example of a spectral interference. Stray radiation
How might you correct for chemical interference? Use a chelating agent, or use a hotter flame
Explain how alkali metals can be an issue during atomic spectroscopy. They ionize really easily, which is not the goal.
How might alkali metals be useful? Because the ionize easily, they produce electrons, which can be used to push the equilibrium of another chemical the correct way.
In FAAS, what is the cathode filled with? The same metal as the analyte.
What are the steps that a furnace goes through in flameless AA? Dry Ash Vaporize Cleaning
At which step in flameless AA is the absorbance read? Vaporization
Which has a greater sensitivity: flame or flameless? Flameless
Differentiate between sequential and simultaneous ICP. Sequential only tests one element at a time, and uses a diffraction grating. Simultaneous tests multiple elements and uses an echelle grating.
How does viscosity affect spectroscopy? Higher viscosity reduces nebulization, and reduces the signal.
How does boiling point affect spectroscopy? A higher boiling point reduces desolvation efficiency and reduces the signal.
How would dissolved solids affect spectroscopy? They reduce nebulization and may clog delivery.
What are some methods of background correction? Use blanks Use a deuterium lamp to absorb background molecules. (Continuum)
What is a disadvantage of continuum source correction? It may under or over correct the readings. Wide slit Vapor is not homogenous.
Created by: swilson67