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Evaluative Revision
Mass Spectrum
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Used to identify unknown compounds
Used to determine the abundance of each isotope in an element
For example it is used to detect banned substances
It determines the mass of a molecule by measuring the mass to charge ratio of ions
4 stages
 Ionisation: electrons are removed from the sample using an electron gun
creating ions
 Acceleration: The ion are propelled into a mass analyser
 Deflection: The ions are then deflected according to their mass using a
magnetic field
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Fragmentation is the process where a positive ion splits into fragments
forming a positive fragment ion
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Alkyl groups can identified by their mass numbers on the x axis
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If this quantity is obtained by two readings times it by two
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If this quantity is obtained by two readings times it by two
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Carbon dioxide gas
can dissolve into water so when using the measuring
cylinder method used carbonated water
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Therefore we can
measure the gas given off without having to remove
the bung
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When the solution has been run out the bottom of the pipette should touch the surface
of the solution
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Funnel needs to be removed from the burette so that no extra solution drops into the
burette
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If the solution is not mixed thoroughly into the solution then extra solution may be
needed to reach the end point
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Loss of heat to surroundings is almost
impossible to prevent
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So the registered temperature rise is less than it should be
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Grinding the solid into powder increases the surface area
to increase the rate of reaction
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A lid and lagging of the container help to keep in the heat
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Although increasing the concentration of a reagent that is in excess will have
little effect
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Thermal Decomposition
We need to make sure that the crystals have been heated
sufficiently so that all of the water has been removed
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To prevent this we do a check to
see that further heating of the sample does not lead to
decrease in the mass
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Which could
break off the anion of the crystal and produce a gas so that
it is seen as more water of vapour is given off
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To stop this the crystals need to
be heated with care
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Water may be reabsorbed into the crystals after the experiment as they cannot be
weighed straight after because they will be too hot
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The solid needs the be heated with a blue flame
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When drawing graphs think whether this change may increase or decrease the rate of
reaction
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Preparation of Organic Compounds
Refluxing is used when reagents are slow to react and have to be mixed continuously at
a raised temperature
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Steps required are refluxing, distillation, purification and re distillation

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