Chromatography Practical Questions
Leaves change colour in Autumn, partly due to loss of chlorophyll. Describe how chromatography could be used to show chlorophyll is lost?
1. Carry out chromatography at different times 2. Find the Rf value of chlorophyll 3. Look for a substance at the predicted position/green substance
Explain why it would be better to use Rf values to see if a pigment on your chromatogram was the same as a pigment on another students rather than the distance moved by pigment spots?
1. The Rf value is constant for a given pigment 2. as it is a proportion 3. whereas different distances may have been moved by both the solvent and pigment on the other chromatogram
Suggest why you were told not to move the universal bottle once you had put the filter paper in it?
1. The solvent would not run straight, it would run off the sides
Explain why you should find the distance moved by the pigment by measuring tok the centre of the pigment spot?
1. This would standardise readings 2. Allowing for comparison 3. As pigment spreads out and moves different distances 4. So the centre is the mean/average distance moved by the pigment
Holly usually has dark green leaves. Explain why some cultivated varieties, with yellow leaves grow more slowly?
1. Yellow leaves have less/no chlorophyll 2. Therefore less/no photosynthesis 3. So no production of glucose for use in growth/synthesis of products for plant growth e.g. proteins...
Explain why it was necessary to draw the line to show the solvent front before the filter paper dried?
Once dried, you cannot see the solvent front.
You were told to use pencil to mark the origin. Suggest why it was important not to use pen?
The pen ink would contain pigment which would dissolve in the solvent separating out, obscuring results.
Suggest why xerophytic plants cannot have pigment extracted by crushing the leaf onto filter paper?
Xerophytic plants have a thick waxy cuticle to prevent water loss, therefore this method may not be sufficient to break the waxy cuticle.
