A2 Chemistry - Unit 1 Module 3 analysis summary

Summary notes made on F324 module 3 analysis from my OCR chemistry textbook (blue with SEM of a growing fluropatite crystal on cover)! Words in light blue are definitions that need to be learnt and the 3 sections in dark blue are included in the textbook for background knowledge but are NON-EXAMINABLE!

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Chemistry: Unit 1 Module 3
analysisrevision
Basics of chromatography
Chromatography is a technique used to separate components in a mixture and identify them by
comparing their Rf/retention time value to a database.
Mobile phase ­ the phase that moves liquid or gas
Stationary phase ­ the phase that doesn't move solid or liquid
Chromatography works on the basis that different components have different affinities for a
stationary and mobile phase. The greater the interaction the component has with the stationary
phase the more it is slowed down; the difference in speeds is what creates the separation.
Methods of separation:
Adsorption solid or liquid stationary phase
Relative solubility liquid or gas stationary phase
Adsorption ­ the process by which a solid holds molecules of a gas or
liquid or solute as a thin film on the surface of a solid or, more rarely,
a liquid.
Methods of chromatography
Thin layer chromatography (TLC) Gas chromatography (GC)
Method of Adsorption Relative solubility
separation
Mobile phase Liquid solvent Carrier gas (inert unreactive gas, usually
helium or nitrogen)
Stationary Silica gel(SiO or alumina (Al
2)
2O 3)
Adsorbent (thin layer of a solid or liquid,
phase supported on a sheet of glass or such as a long-chained alkane (l) or
plastic silicone polymers (s), coated on the inside
of coiled capillary tubing in an oven)
Method/proces Draw a sample line on the Sample mixture is injected into the
s TLC plate and pipette small gas chromatogram and is vaporised
drops of your sample(s) on Vaporised mixture is forced through
this line the capillary column due to the
Place the plate in a tank with pressure from the carrier gas
a small volume of solvent that Components dissolve into/ adsorb to
should be higher than the the stationary phase and depending
sample line on the strength of their interactions
Cover the tank and allow the determines the rate at which each
solvent time to soak up the component moves through the
plate and then take it out capillary column
before the solvent runs off A detector records the retention
the edge time (how long it takes to travel
Mark the solvent line and through the capillary column) of each
allow the remaining solvent component
to evaporate The results are processed by a
Analyse the plate by circling computer and are then displayed in a
the spots and calculating the gas chromatogram

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Rfvalue(s) ­ if the samples
aren't visible use a UV light
Limitations Similar compounds often Thousands of chemicals have the
have similar R fvalues ­ same retention time, peak shape and
components hide behind each detector response, so it doesn't
other positively identify most components
Unknown compounds have Unknown compounds have no
no reference Rf value for reference retention time for
comparison­ the analyst comparison ­ the analyst needs to
needs to have a vague idea have a vague idea what the
what the component…read more

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A strong magnetic field, applied using an electromagnet, and low-energy radio frequency radiation
are required for NMR spectroscopy.
Nuclear spin (non-examinable) :
Protons and neutrons are collectively known as nucleons.
Nucleons can `spin' in one of two directions
Opposite spins pair up, but if there is an odd number of nucleons
then a small residual nuclear spin is produced ­ which generates a
magnetic field and a signalon an NMR spectrum.…read more

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The number of peaks on the spectrum is equal to the number of different carbon environments
the molecule contains.
The chemical shift is equal to the type of carbon environment, it can be deduced using a
datasheet.
Size of the peak tells us nothing!
1
H-NMR
The number of peaks on the spectrum is equal to the number of different hydrogen environments
the molecule contains.
The chemical shift is equal to the type of hydrogen environment, which can be deduced using a
datasheet.…read more

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Advantages Disadvantages
Harmless (unlike x-rays only use Cannot be used on patients with
low-energy radio-frequency radiation) ferromagnetic metal (Fe, Co, Ni) implants
Non-invasive less risk of further or those metals in any other form as they
complications/injury or infection will be attracted to the electromagnet
People with pace maker cannot use them
as the device is affected by the strong
magnetic field
Fragment ion M/z value
CH3 +
17
CH
2CH 3
+
29
+
CH2 CH2
CH3
or CH 3CO+ 43
CH CH CH…read more

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