Download 4. Chromatography of leaves

Classic chemistry experiments
4.
9
Chromatography of
leaves
Topic
Separation of mixtures, extraction.
Timing
30 min.
Description
Students use chromatography to separate the pigments present in a leaf.
Apparatus and equipment (per group)
▼ Mortar and pestle
▼ Chromatography paper
▼ Teat pipette. Use the type of teat pipettes (usually fitted to Universal Indicator
bottles) that do not allow squirting – eg Griffin.
3
▼ 100 cm Beaker
▼ Small capillary tube to transfer drops of liquid onto chromatography paper.
Chemicals (per group)
Propanone (Highly flammable)
Sand
Cut-up leaves or leaves and scissors.
Teaching tips
This works well if a very concentrated solution is prepared. Use cut up leaves, a pinch
of sand, and a few drops of solvent. (Some separation may occur at stage 6).
Background theory
Different substances have different attractions to the paper.
Safety
Wear eye protection. Avoid naked flames.
Answers
1. Two.
2. Green and yellow.
3. Yellow moved further than green.
10
Classic chemistry experiments
Chromatography of
leaves
Introduction
Most leaves are green due to chlorophyll. This substance is important in photosynthesis
(the process by which plants make their food). In this experiment, the different
pigments present in a leaf are separated using paper chromatography.
Pencil
Strip of chromatography
paper
Beaker
Spot of pigment
Pencil line
Propanone
What to record
The chromatogram produced in this experiment can be dried and kept.
What to do
1. Finely cut up some leaves and fill a mortar to about 2 cm depth.
2. Add a pinch of sand and six drops of propanone from the teat pipette.
3. Grind the mixture for at least three minutes.
4. On a strip of chromatography paper, draw a pencil line 3 cm from the bottom.
5. Use a fine glass tube to put liquid from the leaf extract onto the centre of the line.
Keep the spot as small as possible.
6. Allow the spot to dry, then add another spot on top. Add five more drops of
solution, letting each one dry before putting on the next. The idea is to build up a
very concentrated small spot on the paper.
7. Put a small amount of propanone in a beaker and hang the paper so it dips in the
propanone. Ensure the propanone level is below the spot.
8. Leave until the propanone has soaked near to the top.
9. Mark how high the propanone gets on the paper with a pencil and let the
chromatogram dry.
Safety
Propanone is highly flammable. Wear eye protection.
Questions
1. How many substances are on the chromatogram?
2. What colours are they?
3. Which colour moved furthest?