PART 1
This assignment requires me to show and explain how I used different techniques
to separate a range of substances from several different mixtures.
Extraction of plant pigments
Within this assignment I learnt how to extract leaf pigments by using different
solvents, which include: water, ethanol and propanone. In this practical, the
pigment in which I was extracting was paprika.
1. Firstly, I began by choosing a plant pigment which was paprika and added
this into a pestle and mortar accompanied by some sand to speed up the
grinding process of turning the paprika into a fine powder
2. The first solvent I used was propanone, I added this to the pestle and
mortar with the paprika in and added it bit by bit, so I didn’t over dilute the
paprika
3. Once the paprika was no longer a powder and had turned into a liquid
consistency, I added this to a container with a label to show me which
solvent I had used
4. I then repeated this process of grinding the paprika and adding the solvent
again however changing the solvent each time to water and ethanol
5. At the end of my extractions I had 3 containers: paprika and propanone,
paprika and water and paprika and ethanol, each with labels on
We chose propanone as it is less polar than water but not non-polar so therefore
it is mid-polar. This means you can extract your plant pigment even if it is non-
polar or highly polar. Ethanol is more polar than propanone but less polar than
water, this means the paprika will dissolve more in ethanol than in propanone
and will travel up the paper chromatography more slowly. Water is the most
polar so therefore due to the high polarity the paprika will dissolve the most and
also the water mixture will travel up the paper the slowest.
In completed a trial experiment of my own investigating the effect of polarity of
solvent on the solubility of solids. I found water fully dissolved all of the solids due
to having a high polarity. Ethyl ethanoate dissolved two out of 3 of the solids, this
could be due to being mid-polar, suggesting ethanol may have the same result to
mixing with the paprika plant pigment. Hexane didn’t dissolve any solids and I
know this is because it is non-polar. These results show that the more polar the
, Biology- Assignment 3 separate to identify
solvent is then the more likely it is to dissolve solids, suggesting water will dissolve
the paprika fully.
Chromatography of extracted plant pigments
Within this assignment I learnt how to do chromatograms for plant pigments. I
used thin layer chromatography and paper chromatography.
Thin Layer Chromatography
1. I drew a start line, in pencil, 1 cm up from the bottom of the TLC on the
chalked side. This is done in pencil, so it doesn’t dissolve and move up the
TLC.
2. Next, using a micro capillary tube I took out a small amount of my mixture
from my containers in which I had previously prepared, the first container
was paprika and water
3. I then dropped a small amount of the liquid onto the pencil line creating a
small dot onto the center
4. Each time I dropped the liquid onto the line I would use a hairdryer to dry
the liquid to ensure the liquid didn’t spread
5. I would drop a small amount of the liquid on multiple times and using a
hairdryer in between each drop to create a very concentrated dot to get
the best results on my TLC
6. After that, in the bottom of a test tube I added a small amount of 9:1 (9:1
petroleum ether: propanone) and then used tweezers to add my TLC into
the tube ensuring the solvent didn’t go past the pencil line and that my TLC
wasn’t directly touching the sides
7. The solvent would travel up the TLC and when it was nearly at the top, I
took the TLC out of the tube and drew another pencil line where the end of
the solvent had travelled
8. I would repeat this using my container of paprika and propanone
Paper chromatography
1. I drew a start line in pencil 1 cm up from the bottom
2. Next I, repeated steps 2-5
3. This time adding 9:1 petroleum ether: propanone into a boiling tube
4. I used a bung with a hook on the end and hooked the paper
chromatography onto it measuring the length from the solvent ensuring
the solvent didn’t go past the start line
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