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Characterization Techniques CHEM 241-08A - Coggle Diagram
Characterization Techniques CHEM 241-08A
Melting Points
Technique Overview
Helps determine the purity of an organic compound.
Aids in the identification and verification of an organic compound
How it Works
Mixture Melting Point Method
Take quick/raoid melting point of compound to obtain approximate melting point range
Obtain an actual melting point range of the compound
Control the rate of heating, gradually lowering heat control when within 10°C of approximate melting point range
Heat sample at rapid rate
Video: [Carrying Out a Melting Point Determination](
https://www.youtube.com/watch?v=sh-96_KfqgY&feature=youtu.be0
Pros/Cons:
Pros: can be done rather quickly, inexpensive, great if already suspecting an identity, only requires a small sample amount
Cons: can only be used for solids, destroys the sample, samples with more than one solute can not be analyzed for purity
When to Use MPM:
can be used to assess the purity of a substance by finding the melting point depression of the different substances
can be used both in the lab and in quality control checks for various industries
NMR Spectroscopy
How it Works:
[Video: How to Prepare an NMR Sample]
(
https://www.youtube.com/watch?v=UhP_GG7qT9M
)
molecules are placed in a magnetic field, and their respective nuclei behave like magnets
the resonating nuclei are measured and placed in an NMR spectrum which displays the frequencies as peaks on a graph
the height of each peak can be used to determine the intensity of each signal
the signals give information about the atoms, such as the properties of the neighboring atoms and their 3-D structures
When to Use NMR:
when two compounds have the same molecules but different properties
to identify structure and understand properties
Pros/Cons:
Pros: can be done quickly, does not destroy sample, is reproducible, quantitative, and can be easily setup
Cons: is expensive, hard to detect structures of high MW molecules, can be dangerous to operate, can only detect nuclei having magnetic moments
Gas Chromatography
Technique Overview
Separates mixtures of compounds based on polarity differences and affinity for a stationary versus a mobile phase
Video: [Gas Chromatography]
(
https://www.youtube.com/watch?v=UycPljfrnWo
)
How it Works
Prepare a sample of dry powder compound
Assemble the column using the Dry Packing Method
Load the column and add the sample
Ensure the column does not dry out throughout the duration of the experiment. Maintain a minimum of 1 cm length of solvent above the alumina in the column.
Elution and Flash Chromatography
When to Use Gas Chromatography
used when substances need to separated + you need to find how much of the component is present or absent
used with organic molecules or gases
Pros/Cons
Pros: can be done rather quickly, produces good quantitative data, very accurate, only small sample needed
Cons: limited to thermally stable and volatile compounds, soluble samples that do not react w/ column
Thin Layer Chromotography
Technique Overview
method for analyzing mixtures by separating compounds in the mixture
Video:
[link to www.youtube.com]
(
https://www.youtube.com/watch?v=lj5OWzhZSac
)
can determine the number of components in a mixture, the identity of the compounds, and the purity of a compound
How it Works:
Stationary Phase: Uses a thin, uniform layer of silica gel or alumina coated onto a piece of glass, metal or rigid plastic
contains a substance that fluoresces in UV light
pencil line drawn near the bottom of the plate with small drops of solution of the mixture, plate is placed in beaker with shallow layer of solvent, cover the beaker, solvent travels up plate, the rates of the different components of the mixtures travel at different rates
Rf values: divide the distance travelled by the component/distance travelled by solvent
Pros/Cons:
Pros: Easy way to separate components, can be done rapidly, feasible to visualize all components of UV light, only small sample sizes required
Cons: results are difficult to reproduce, only soluble components of the mixtures can be used, only qualitative analysis is possible, can be affected by temp. and humidity
When to Use TLC:
when you are dealing with a small amount of materials
easy to separate many different mixtures
can help to determine the progress of a reaction, and the purity of the compounds within the mixture
