Required Practical 7: Chromatography to investigate the pigments from leaves of different plants Flashcards
Use of chromatography to investigate the pigments isolated from leaves of different plants
What is the aim of this practical?
This practical’s aim is to investigate the different pigments isolated from different leaves through chromatography
What is the purpose of chromatography in this practical?
Chromatography is used to separate and identify the pigments present in the leaves of different plants
What are the key pigments found in plant leaves?
Chlorophyll a - main pigment for photosynthesis
Chlorophyll b - accessory pigment
Carotenoids - absorbs light and protects chlorophyll from damage
Xanthophylls - another type of accessory pigment
What is the principle behind paper chromatography?
Paper chromatography separates pigments based on their solubility in the solvent and their affinity to the paper.
More soluble pigments travel further up the paper, while less soluble ones remain closer to the baseline
What is the Rf value in chromatography, and how is it calculated?
The Rf value is the retention factor and is calculated using the formula:
Rf = distance travelled by pigment ÷ distance travelled by solvent front
Describe the method for extracting pigments from plant leaves
- Grind the leaf sample with a solvent like acetone or ethanol
- Filter the solution to remove solid debris
- Use the extract for chromatography
Why are shade - tolerant and shade - intolerant plants used in this experiment?
To investigate differences in pigment composition, as shade - tolerant plants may have accessory pigments to capture limited light
What safety precautions are necessary for this practical?
- Using solvents in a well ventilated area of fume cupboard
- Avoid direct contact with solvents, by wearing gloves
- Handle glassware carefully to avoid breakage
What factors can affect the separation of pigments in chromatography?
- Type of solvent used
- Duration of the run
- Consistency of the pigment application on the chromatography paper
Why must the origin line be drawn in pencil, not pen?
The ink from the pen may dissolve in the solvent and run alongside the pigment
Why should you draw a line where the solent reached immediately?
The solvent evaporates very quickly, so the solvent front (the end position) is not visible shortly after the experiment
Why should you measure the Rf value from the middle of the pigment mark?
The pigment mark is spread out, so by measuring from the middle position each time it is a way to standardise the measurements taken. to allow for comparisons
Why should you make sure your chromatography paper is vertical and straight?
This is done to make sure the pigments move straight up the paper to avoid them running off the side of the paper and/por being washed off
