chemical analysis - chromatography Flashcards
what does paper chromatography allow?
separate substances based on their different solubilities
steps for chromatography
- Get a piece of chromatography paper and draw a pencil line 2cm up from the bottom
- draw a dot of your mixture on the pencil line
3.put a small volume of solvent in a tube or beaker - place chromatography paper into the solvent making sure the solvent is below the line
- wait for solvent to rise up the paper
what is the stationary phase in chromatography?
the chromatography paper as it doesn’t move
what is the mobile phase in chromatography?
the solvent as it moves
In the results, if there is one dot for the substance/mixture what does that mean? and what if their is two?
one = pure
two = impure as it is a mixture of
what does a pure compound produce in chromatography?
a single spot in all solvents
what does a compound mixture produce in chromatography?
may somerset into different spots depending on the solvent
what travels further up the paper?
the substances with a high solubility
why do we draw the starting line in pencil?
if we drew the starting line in pen, the pen ink would move up the paper, with the solvent
what is Rf?
retention factor
how do we work out Rf value?
distance moved by substance / distance moved by solvent
(measure from pencil line to solvent front)
what else can we use chromatography for?
identifying unknown substances
what do we use the Rf value for?
identifying an unknown substance
why might we need to repeat paper chromatography for identifying an unknown substance? what do we repeat with?
several different substances could have the same Rf value so we need to repeat with a different solvent
what happens if the unknown substance has never been analysed before?
there will not be an Rf value on the database so carry out further analysis
