Chromatography and Criteria of Purity Flashcards
what is paper chromatography used for?
to see what an unknown liquid is made of
usually dyes, food colouring.. etc
how does paper chromatography work?
a spot of ink is placed on the x mark on the pencil line/baseline and the paper is suspended in water in a beaker
as the water rises up the paper, the different dyes travel different distances due to their different solubilities and so are seperated on the chromatogram
what is the retention factor?
retention factor or (Rf) for a particular substance compares the distance travelled by the substance to the distance travelled by the solvent
formula retention factor
distance travelled by substance
/
distance travelled by solvent
why will the retention factor always be __________ than __?
less than 1
the solvent will always travel further than the substance
what else can rf values be used for?
to compare substances to identify them
the same substance will always have the same rf value in the same solvent
how can colourless liquids be seperated by chromatography?
a UV light is used to see the spots
how can we check the purity of a liquid/ solid
boiling point
melting point
a pure substance has a ________ ________/________ point
sharp exact boiling/melting point
an ______ solid will have a ________ than the pure solid
impure
lower melting point
a liquid ____________ will have a higher _____ point than the pure ______
a liquid containing a solute will have a higher boiling point than the pure solvent
pure water boils at 100 degrees celsius, salted water boils at
102 degrees celsius
pure ice melts at o degrees celcius,ice with salt added melts at
-4 degrees celsius
why is the purity of food products
they must not contain contaminants as these could have a negative effect on the patient or consumer
why is the pencil line drawn in pencil?
pencil does not dissolve in water as easily
pen would travel up the paper and interfere with the inks being tested as it is soluble
