Term
| Outline the process of spectroscopy |
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Definition
| Shine light at sample -> Causes sample to do something -> Measure emission or absorption of energy |
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Term
| What two types of analysis can spectroscopy perform? |
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Definition
| Quantitative or qualitative |
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Term
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Definition
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Term
| The energy of IR radiation is used to ______ molecules |
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Definition
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Term
| The energy of UV radiation is used to _______ molecules |
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Definition
| Cause electronic transitions within |
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Term
| What is IR spectroscopy primarily for? |
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Definition
| Identification of functional groups |
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Term
| On which axis would you find Transmission shown on a IR spectrograph? |
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Definition
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Term
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Definition
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Term
| What are the units for Wave number? |
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Definition
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Term
| What attachment is required for a machine to scan solids without a KBr disc? |
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Definition
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Term
| What would you do if your solvent absorbed in the same range as your sample? |
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Definition
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Term
| What is useful about the fingerprint region? |
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Definition
| Every compound has a specific fingerprint region |
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Term
| What is the absence of a signal definite proof of? |
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Definition
| A functional group is not present |
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Term
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Definition
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Term
| What relation is the colour seen to the colour absorbed in UV - vis spectroscopy? |
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Definition
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Term
| What does the Beer-Lambert law state? |
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Definition
| Concentration is proportional to absorbance |
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Term
| What is the Beer-Lambert Law? |
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Definition
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Term
| In UV - Vis: Signal response is proportional to? |
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Definition
| Intensity of light received |
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Term
| How do atoms or molecules commonly change in spectroscopy? |
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Definition
Electronically - emission or absorption
Magnetically - spin |
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Term
| How is the compound identified in spectroscopy? |
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Definition
| By identifying functional groups |
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Term
| What does a spectrometer do? |
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Definition
| Records changes when energy interacts with molecule and when the energy is removed |
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Term
| How is IR spectroscopy carried out? |
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Definition
-A beam of electromagnetic radiation in IR region is shone from heated ceramic rod on liquid or solid sample
-Functional groups absorb energy and move between different vibrational quantum levels |
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Term
| What data is used to plot data in IR spectroscopy? |
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Definition
| The difference in energy from sample beam and reference beam |
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Term
| What type of data does IR spectroscopy give? |
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Definition
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Term
| What does a monochromator do? |
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Definition
| Removes wavelengths of other lights |
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Term
| What are the four forms a sample can be in in IR spectroscopy? |
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Definition
1) Solid state
2) Thin film (dispersion)
3) Thin film (neat)
4) Solution |
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Term
| How is a sample for solid state IR spectroscopy? |
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Definition
| Finely ground sample mixed with dry KBr and pressed into disk |
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Term
| How is a sample for thin film (dispersion) IR spectroscopy? |
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Definition
| Finely ground sample dispersed in liquid and held between two windows |
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Term
| How is a sample for solution IR spectroscopy? |
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Definition
| Sample dissolved in solvent and placed into cell with end windows |
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Term
| How is a sample for thin film (neat) IR spectroscopy? |
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Definition
| Sample dropped onto a window and covered with another window |
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Term
| Why is H2O not used as a solvent in IR spectroscopy? |
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Definition
| It would dissolve NaCl windows |
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Term
| Why are glass and silica not used for windows in IR spectroscopy? |
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Definition
| They are opaque at 4000 - 200cm^-1 |
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Term
| What are some problems to avoid when performing IR spectroscopy? |
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Definition
-Solvents that absorb in same region as sample
-Coarsely ground samples that give broad peaks
-Moisture from not wearing gloves fogs windows
-Using wet solvents or damp solvents for washing windows |
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Term
| What is the disadvantage of peaks being broad? |
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Definition
| Unable to determine whether one or two peaks and what range they are in |
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Term
| What types of vibrations do molecules give off? |
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Definition
-Symmetrical stretching
-Asymmetrical stretching
-Scissoring
-Twisting
-Bending
-Wagging |
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Term
| What are the strengths of IR spectrometry? |
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Definition
-Pattern of bands 1400-1600cm^-1 very sensitive to small structural changes
-Absence of peak is proof structure isn't there
-Correspondence with a known sample's IR spectrum is strongly indicative of the compound |
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Term
| What are the weaknesses of IR spectrometry? |
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Definition
-Some signals ambiguous or overlap
-Functional group assignment is an indication but not confirmatory
-Complex spectra may hide differences
-IR analysis alone is rarely confirmatory of a structure |
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Term
| What happens when visible light hits molecules containing d block metals? |
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Definition
| The d block metal ions absorb light and promote electrons to the next energy level |
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Term
| What happens when visible light hits organic molecules containing conjugated or delocalised unsaturated bonds? |
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Definition
| They absorb energy to assist movement of electrons within the molecule - chromophores |
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Term
| Why do some molecules appear to have a colour when it is exposed to white visible light? |
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Definition
| They absorb certain wavelengths of light and the rest given off is the wavelengths they didn't absorb |
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Term
| Why is chlorophyll green? |
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Definition
| It absorbs violet and red light |
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Term
| What does each term (eg A) represent in the Beer Lambert law equation? |
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Definition
A = absorbance
ε = molar absorptivity
l = path length
c = concentration |
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Term
| How is quantitative analysis for a substance using UV-Visible light spectroscopy carried out? |
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Definition
-Prepare standard solutions
-Measure their absorptivity
-Plot absorption against concentration |
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Term
| What does a colorimeter for visible light consist of? |
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Definition
-White light source (Tungsten filament)
-Prism or diffraction grating (monochromator)
-Slits or colour filters to select wavelengths
-Holder for sample/reference cells
-Photomultiplier detector |
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Term
| What is the monochromator for? |
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Definition
| Splitting light into different wavelengths |
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Term
| What is signal response proportional to in visible light spectrometry? |
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Definition
| Intensity of light received, plotted as either percentage absorbance or transmission |
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Term
| What are cells (/cuvettes) made from in visible and UV light spectroscopy? |
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Definition
Visible - plastic, glass
UV - quartz or silica |
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Term
| Why can't cells (/cuvettes) made from plastic and glass be used for UV light spectroscopy? |
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Definition
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Term
| How is light spectroscopy carried out? |
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Definition
-Sample or blank put into cuvette, cuvette wiped dry
-Sample put into spectrometer once it is set on correct wavelength and calibrated |
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Term
| How is the correct wavelength for spectrometry found? |
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Definition
-By using reference books or data sheets
-unknown biological samples should be analysed using whole spectrum |
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Term
| What is the disadvantage of single beam light spectrometers? |
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Definition
| Light source intensity may vary between measurements giving inaccurate readings |
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Term
| How is the problem of light intensity changing overcome? |
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Definition
| With double beam spectrometers that measure the blank and sample together |
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Term
| How do double beam spectrometers reduce error? |
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Definition
| So the difference between the blank and sample is always measured accurately, even if the light intensity changes between samples |
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Term
| What provides the light source in UV spectrometry? |
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Definition
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Term
| What does a double beam UV light spectrometer contain? |
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Definition
-Prism or diffractive grating splits light into components
-half mirrored device splits each component into two beams
-Each beam passes through cuvette containing sample |
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Term
| How is data from light spectrometry analysed? |
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Definition
| Absorbance is plotted onto graph, shape and location of peaks are related to functional groups using a data sheet |
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Term
| What must be done to ensure the results of light spectrometry are accurate? |
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Definition
-Narrow wavebands used
-Keep spectrometer spotlessly clean
-Service spectrometer regularly
-Use low concentrations (too high and the signal transmitted is too weak) |
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