Chromatography
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What is chromatography used for?
It is used to separate individuals of a mixture and subsequently identify them
Describe how thin layer chromatography of photosynthetic pigments can be carried out
• crush plant in pestle and mortar and add a solvent e.g. acetone • draw a pencil line near the bottom of the silica gel • using a capillary tube, drop sample onto centre of pencil line • repeat 10 times, allowing for drying inbetween • place in solvent ensuring line of solvent is below pencil line • seal chromatogram in jar with solvent • remove before solvent reaches top of chromatogram
What is used to identify substance from a chromatogram?
Rf values
How can Rf values be calculated
distance moved by pigment from origin/ distance moved by solvent front from origin
What does Rf stand for?
Relative front
What affects the rate at which substances move?
• solubility in the solvent used • size of the molecule • polarity of the molecule
What is the stationary phase in TLC?
Silica gel
What is the mobile phased in TLC?
The solvent
How can an Rf value be used to identify a substance?
The Rf value of a certain molecule in a certain solvent can be looked up in a table of values and compared
How is 2 way chromatography completed?
• normal one way chromatography is run - the chromatogram is then turned 90 degrees and a different solvent is used
Why is 2 way chromatography used?
When substances in the chromatogram have similar Rf values and need further separation