Required Practical 7- Chromatography

Question 1

Aim of chromatography practical

Answer 1

To investigate the different pigments isolated from different leaves through chromatography

Question 2

Background of chromatography

Answer 2

Each pigment of chlorophyll absorb different wavelengths of light and plants are adapted to their environment by having different proportions of each pigment to maximise light energy absorption

Question 3

Hypothesis for chromatography RP

Answer 3

The combination of pigments and proportion of each pigment will differ in the leaves from plants from different environments

Question 4

Method of chromatography RP

Answer 4

1. Extract pigment from the leaf ( crushing leaf onto chromatography paper or crushing leaf in solvent
2. Draw a PENCIL line (origin line) on the chromatography paper,5 mm higher than the solvent will be
3. Add a drop of the pigment in the middle of the pencil line made of the chromatography paper using the tip of a plastic pipette
4. Allow this to dry and then repeat until the pigment dot is 3-5mm in diameter
5. Once fully dry, place the chromatography paper in the container of solvent, making sure the solvent is below the origin pencil line and that the paper is straight vertically
6. When the solvent has moved up the paper (by being absorbed into the chromatography paper,as it does so it will dissolve the pigments and whichever pigments are more soluble will move further up the paper) so that it is 2mm from the top ,use forceps to remove
7. Immediately draw a pencil line to show the end position of the solvent, and a circle around each pigment mark
8. Calculate rf values to identify which pigments are present in the leaf
9. Repeat on second plant species

Question 5

What is an Rf values

Answer 5

To identify pigments present on the chromatography use pigment rf values
The rf value will be constant for each pigment dissolved in a particular solvent,as it depends of solubility of the pigment in that particular solvent

Question 6

What is the rf value equation

Answer 6

Rf= distance moved by pigment/ distance moved by solvent

Question 7

Conclusion of chromatography RP

Answer 7

Compare the chromatography and the different rf values to see if the different plnt species contain the same pigment

Question 8

Why must the origin line be drawn in pencil not pen ?

Answer 8

Ink from a pen would dissolve in the solvent and run

Question 9

Why should you draw a line where the solvent reached immediately?

Answer 9

The solvent evaporates v quickly so the solvent front isn’t visible shortly after the experiment

Question 10

Why should you measure the rf value from the middle of the pigment mark ?

Answer 10

The pigment mark is spread out,so by measuring from the middle position each time it is a way to standardise the measurements you’re taking to allow for comparisons

Question 11

Why should you make sure your chromatography paper is vertical and straight ?

Answer 11

So the pigments move straight up the paper to avoid them running off the side or being washed off