chemistry - C2 - quantitative chemistry - chromatography

chromatography questions with answers ... hope it helps :) 

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  • Created on: 11-09-12 20:03
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Chemistry chromatography Revision
Question: How does gas chromatography separate the
substances in a mixture of gases?
Answer: The mixture of gases is injected into the machine
and vaporised. The sample passes through a long column
packed with a solid that is wound into coil. An inert gas
such as nitrogen is passed through the column to move the
sample through, this inert gas is known as the inert gas and
the column is known as the stationary phase. different
substances in the mixture have different affinities for the
mobile phase and the stationary phase , this means the
substances travel through the column at different speeds so
reach the detector at different times and so are separated
Question: What is instrumental analysis, what is it used for
and why is it so useful?
Answer: it is the identification of elements and compounds
using instrumental methods ­ this just means using
machines. Instrumental methods are useful because they are
very sensitive and can detect even the tiniest amounts
substances, they are very fast and tests can be automated.
Instrumental methods also have the advantage of being very
accurate
Question: in mass spectroscopy, a molecular ion is formed.
What is a molecular ion?
Answer: this is an ion formed by the otherwise un-fragmented
molecule in spectroscopy. Molecular ions form when molecules
loose an electron in mass spectroscopy.

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Question : what is key piece of information do we find from
mass spectroscopy in order to help identify a compound
Answer : the Mr , which is the peak furthest to the right
which is the molecular ion peak and shows the Mr of the
substance
Question: how does paper chromatography separate the
substances in a mixture?
Answer: a sample of the mixture is placed on a piece of
chromatography paper, and then a solvent is added.…read more

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Question : in paper chromatography why must the solvent be
below the spots
Answer : so the substances don't dissolve in water
Question: what is paper chromatography used for?
Answer :analysing coloured substances , such as the coloured
pigments in plants and artificial colours used as food
additives
Question: what is RF value?
Answer :distance moved by "spot"/distance moved by solvent
Question: in paper chromatography why must you wait until
the water is near the top of the paper before taking it out to
dry?…read more

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Answer: so that the dye out of the pen didn't dissolve in the
water and travel ups the chromatography paper.…read more

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Largest substance in mixture = 111
Mass spectroscopy
Mr = 100
Paper chromatography…read more

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