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CHEM 2368
Spectroscopy
| Question | Answer |
|---|---|
| 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
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