I completed chemistry A-Level in one year, teaching most of the course to myself, earning an A overall. I found it easiest like this as all the information from the textbook is streamlined and in one place. Comparing all past mark schemes I wrote the summaries using words and highlighting phrases y...
Mobile phase: carries the soluble components of mixture
with it up the plate, the more soluble the faster it moves.
Stationary phase: hold components back in the mixture
that are attracted to it, the more affinity the solvent has
to it the slower it moves.
Thin layer (TLC) is better than paper chromatography
because
• it runs faster
• Smaller amounts of mixtures can be spread
• The spots spread out less (more accurate Rf values)
• The plates are more robust
Column chromatography uses a powder (silica) as the
stationary phase which is packed in a narrow tube and
the solvent is added to the top . The components in the
mixture moves at different rates and so can be collected
into different conical flasks.
• large amounts can be separated
• Large amounts can be collected
Gas-liquid chromatography (GC), stationary phase is
a powder coated with oil which is packed in a long
capillary tube coiled and put in an oven. Mobile phase
is an unread give gas (nitrogen / helium).
Components are separated as they have different
retention times, you can measure thermal conductivity
of the gas produced. Or can be linked with other
apparatus for further identification such as NMR,
mass spectrometry etc.
Gas chromatography-mass spectrometry (GCMS) is
where a mass spectrometer is used as a detector for gas
chromatography, as each component moves across the
column the time taken to do so is calculated and fed
into a mass spectrometer which identifies the
component based on it’s accurate mass /
fragmentation pattern.
Common Exam Questions:
“What are the benefits of using thin layer
chromatography”
“A student did this experiment, state an amount of
things that are wrong with the apparatus / experiment
that would give unreliable or inaccurate results”
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