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Characterization Techniques CHEM241-01A, Qualitative Analysis, Only a…
Characterization Techniques
CHEM241-01A
Melting Point
Melting point works to determine the purity of an organic compound or to help identify an organic compound.
This technique can be used to identify a specific compound within a mixture
Melting point is defined as the temperature at which a solid becomes liquid. Each compound has their own unique melting point that characterizes them
This technique is used on solids
Pros :
Cons:
for identifying compounds within a mixture, the melting points must be known beforehand
This technique can only be used on organic compounds
Every compound has a melting point
It is a quick and easy procedure to do
https://www.youtube.com/watch?v=c-_N8grg-OY
Thin Layer Chromatography
Thin Layer Chromatography is a great technique used for identifying compounds and following the progress of a reaction
It is appropriate to use this technique on liquids
Pros
Cons
Results are difficult to reproduce
Easy to use
https://youtu.be/CmHFVxTxkGs
Gas Chromatography
Gas Chromatography helps separate volatile components in a mixture by boiling point and vapor pressure
How it works:.
Sample to be tested is mixed with appropriate solvent such as heptane, acetone, or methanol. Then is injected into column at relatively high temperatures to rapidly vaporize the sample. After the sample is separated by the different phases it is detected by the detector at the end of the column.
The stationary phase is packed in the inner wall of the column usually made of silicon grease or wax (to withstand high temp).
The mobile phase is usually an inert gas such as helium or nitrogen.
Separation rate depends on the interactions of molecules between the stationary phase and mobile phase.
The less volatile molecule interacts more with the stationary phase and moves slowly down the column.
The more volatile molecule reacts more with the mobile phase and moves fast down the column.
Volatile compounds are compounds that easily vaporize at room temperature.
Pros:
Gas chromatography is efficiency so it enables the separation of complex mixtures
It gives an accurate representation of the quantity
Sample analysis is quick
Only a small sample is needed
Cons:
GC is limited to volatile compounds.
Also limited to thermally stable compounds
1H NMR spectroscopy
When a molecules is placed in a strong magnetic field, the nuclei of some of the atoms will begin to behave like small magnets. A broad spectrum of radio frequency waves are applied to the sample, causing the nuclei to begin to resonate at their own specific frequencies.
The various frequencies of the nuclei are then measured and converted into an NMR spectrum displayed as peaks on a gragh. The height of each peak represents the number of nuclei that resonates at each specific frequency.
Cons
Relatively new technique
. The signal that can be generated in the NMR experiment is small, which is mostly coupled with the concentration of the nuclei in the sample
Expensive instrument
Pros
You can easily identify and quantify molecules
It requires very small sample volumes
NMR lets you view the molecular dynamics in a liquid or solid while leaving the sample intact for future observation and testing.
NMR spectroscopy is a technique used to determining the content and purity of a sample (solid or liquid) and to also find its molecular structure.
NMR only works with certain nuclei, nuclei with an odd number of either protons or neutrons
Qualitative Analysis
Only a small sample size is required
It is a sensitive method, so you are able to see when you mess up
You can visualize the component with a UV light
Temperature and humidity can impact the results
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https://www.youtube.com/watch?v=UycPljfrnWo
https://www.youtube.com/watch?v=CH-4TtZSvY0