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practical skills procedures
- Module
- Unit 2
- Institution
- PEARSON (PEARSON)
2.3 assignment- Undertake chromatographic techniques to identify components in mixture
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UNIT 2 LEARNING AIM C. UNDERTAKE CHROMATOGRAPHICTECHNIQUES TO IDENTIFY COMPONENTS IN MIXTURES.
CHROMATOGRAPHIC TECHNIQUES.
Chromatography, come from the Greek word khroma which means colour. This method is used to
separate and identify mixture. You can identify the purity of a substance. The method of this technique
is that the liquid moves up in the paper. There are several types of chromatography: paper, TLC, amino
acid identification, gas-liquid chromatography, ion-exchange,
Paper chromatography
Paper chromatography is a method for tiny amounts of material, this type of chromatography uses strips
of absorbent paper which works as stationary paper. Paper chromatography is used to separate mixture
of a substance. Substances moving at a greater distance at different speeds at a specific time. In paper
chromatography, the paper is the stationary phase because it is not moving, and the aqueous and non-
aqueous organic liquid is the mobile phase in which the liquid is moved up in the paper. Paper
chromatography is used to study the process of fermentation, to detect if there are any contaminations
in drinks and food and to analyses the reaction mixture.
The paper used in paper chromatography is created by cellulose fibres, the
important thing of cellulose is that has an OH group because is a polymer
chain, the cellulose attracts water vapor from atmosphere. The absorption
and separation be uncertain on the chemical sample and how chemical is
strongly attracted to the mobile and stationary phase. The paper has a thin
layer of water molecules, this does not affect the results.
In my experiment I used a non-polar solvent which is propane. The non-
polar solvent has a tiny attraction with water molecules that are joined
with cellulose. We cannot use a polar solvent because it spends more time
in dissolve in the paper and less time in the mobile phase, this is causing the polar molecules to have a
high attraction for water molecules and less attraction to non-polar attraction.
Paper chromatography experiment.
Risk assessment
Hazard Risk What could happen Solution
Propanone High Flammable and Wear PPE equipment.
corrosive
Micro capillary tube Medium Fragile, it could be Take it be carefully.
break.
Method.
1- Place 3 spinach leaves into a mortar.
2- Add 10 drops of propanone solution.
, 3- Grind the mixture for a few minutes.
4- Draw a pencil line from the bottom of the paper around 3 cm.
5- Add the solvent to the beaker.
6- Place paper into the beaker and make sure that the level of the solvent rinse until it stops.
7- The time taken was 17 minutes.
8- Calculate the Rf value of each pigment.
Rf calculation.
1st Rf value: A= 6.5 B= 6.8 Rf = 6.5/6.8= 0.955
2nd Rf value: A= 6.4 B= 6.8 Rf = 6.4/6.8= 0.941
3rd Rf value: A= 6.4 B = 6.8 Rf = 6.4/ 6.8 = 0.41
Thin layer chromatography (TLC).
Thin layer chromatography is another type of chromatography which is like paper chromatography, this
is used to analyse colours in fibres. Paper used is made up of silica gel and the plate is made of glass,
metal or plastic. Silica gel has silicon atoms which are attached to oxygen in a giant covalent structure, it
has a polar surface because the molecule of silica has OH group and can form intermolecular forces with
adequate compounds around.
The separation of the compounds depends on how the liquid
moves fast up in the plate when the compound is soluble in the
solvent, and this depends on how molecules are attracted to
the solvent molecules and how the compound sticks to the
stationary phase. The solubility and how strong is the
absorption to the stationary phase is when the solid absorbs
the mixture. Different components will move up more quickly
than others. It is useful to detect pesticides or insecticides in food, identify how a substance is pure.
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