to separate mixtures and can give information to help identify substances
what are mixtures separated by
their solubility (how well a substance in a mixture dissolves in the solvent)
set up ofchromatography
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during set up for chromatography why should we use pencil for the baseline rather than pen
pen would dissolve in the solvent and move up the paper
what is the name given for the pencil line in paper chromatography
base line
what are the two of phases chromatography
stationary phase
mobile phase
what is the mobile phase
substance molecules can move in (e.g. liquid/gas)
what is the stationary phase
substance molecules can't move in (e.g. solid thick liquid)
do substances in the sample remain at one phase through the whole investigation
no, the will constantlyshift between the two
how does the distance travelled by the substance determine how soluble it is
the solutions travelling further up the paper means it was more attracted to the solvent (more soluble) and therefore spent more time in the mobile phase - which makes the solution move faster
the solutions which remained closer to the start suggests that they were more attracted to the paper (less soluble) and therefore spent more time in the stationary phase - which makes the solution move slower
example of a pure compound in chromatography
a pure compound will produce a single spot in all solvents
example of an impure mixture in chromatography
the compounds in a mixture will separate into many different spots
what does the RF value show
the ratio of the distance moved by a compound (centre of spot from origin) to the distance moved by the solvent
calculating RF value
measure the distance travelled by the solvent and each substance
1.5/9.7 = 0.15
3.7/9.7 = 0.38
8.2/9.7 = 0.85
why are no units needed
as the ratio cancels out the units
what does a higher RF value mean
the further up the chromatography paper the substance travelled