Required Practical 7 - Using Chromatography to investigate different photosynthetic pigments

Way pigments from a leaf of a plant can be isolated with paper chromatography

Crush leaves with solvent to extract pigments

draw a pencil line on filter/chromatography paper 1 cm above bottom

add a drop of pigment extract to line (origin)

stand paper in boiling tube of solvent below point of origin

add lid and leave to run

remove before solvent reaches top and mark solvent front with a pencil

why the origin should be drawn in pencil rather than ink

ink soluble in solvent

ink may mix with pigments (origin may move)

why the point of origin should be above the level of the solvent

pigments are soluble in solvent

so would runoff paper/ spots may dissolve in solvent

why a pigment may not move up the chromatography paper in one solvent

may be soluble in one solvent but insoluble in another

Describe how pigments can be identified

Rf value = distance moved by solute/ distance moved by solvent

compare Rf value to published value

why solvent should be marked quickly once chromatography paper is removed

once solvent evaporates solvent front is not visible

why the centre of each pigment spot should be measured

to standardise readings

allowing comparisons to be made

why the obtained Rf values were similar, but not identical, to the published values

different solvent/pigment moves different distances

Rf value is constant for same pigment/ can be compared