rp7

Question 1

describe how pigments from leaf of plant can be isolated with paper chromotography

Answer 1

crush leaves with solvent to extract pigments
draw pencil line 1cm above bottom
add drop of extract to line
stand paper in boiling tube of organic solvent below point of origin
add lid and leave to run and remove before solvent reaches the top and mark solvent front with pencil

Question 2

why should origin be drawn with pencil line

Answer 2

ink soluble in solvent so ink would mix with pigments

Question 3

why point of origin should be above level of solvent

Answer 3

pigments are soluble in solvent so would run off paper

Question 4

rf value

Answer 4

distance moved by spot / distance moved by solvent front

Question 5

explain why solvent front should be marked quickly once chromotography paper is removed

Answer 5

once the solvent evaporates the solvent front won’t be visible

Question 6

explain why centre of each pigment spot should be measured

Answer 6

standardises readings as pigment is spread out
allows comparison to be made

Question 7

explain why rf values are used and not the distance moved by pigment spots

Answer 7

solvent and pigments move different distacnes
rf value is constant for same pigment so allows comparison