Required Practical 7

Question 1

you were told to use pencil to mark the origin.

it was important NOT to use a pen mark this line.

why?

Answer 1

ink would dissolve in solvent

Question 2

it is usual in chromatography to make a solution of the pigments from the leaf and apply to the filter paper.

in your investigation it was NOT necessary to make a solution of pigments.

explain why?

Answer 2

pigments are squashed into filter paper

Question 3

you were told to draw a line to show the solvent front before the filter dried.

explain why it was neccessary to draw the line before the filter paper dried?

Answer 3

cannot see solvent

Question 4

you could use Rf values to find out if a pigment on your chromatogram was the same as a pigment on another students chromatogram.

explain why it would be better to use the Rf value to do this and NOT distances moved by pigement spots?

Answer 4

• Rf value = distance moved by spot divided by distance moved by solvent
• Rf values are constant whilst pigment moves diff distnaces

Question 5

you were told not to move the boiling tube once you had put the filter paper in it.

suggest why this is important?

Answer 5

pigments wouldnt run straight

Question 6

you were told to find the distance moved by the pigment by measuring to the centre of pigment spot.

explain why you should measure to centre of pigment spot?

Answer 6

• pigment moves diff distances
• it is mean distanced moved by pigment

Question 7

the technique you used to extract pigments from leaves may not produce results if it used with leaves from xeroyphytic plants.

use your knowledge of leaves of xerophytic plants to suggest why?

Answer 7

• have thick cuticle
• prevent pigment from being transferred to paper

Question 8

leaves change colour in autumn.

this is partly due to loss of chlorophyll.

describe how you could use chromatography to show chlorophyll is lost?

Answer 8

• carry out chromatography at diff times
• find Rf for chlorophyll

Question 9

holly usually has dark green leaves.

some cultivated varieties of holly have yellow leaves.

explain why these cultivated varieties grow more slowly than holly with dark green leaves?

Answer 9

• yellow leaves have less chlorophyll
• less photosynthesis
• glucose needed for growth