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BTEC Applied Science: Unit 2 Learning Aim C (Chromatography)
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Undertake chromatographic techniques to identifycomponents in mixtures.
Introduction
Chromatography is the process which describes a technique which is used to separate
different components within a mixture, mostly used to find out the unknown compound within
that mixture. It’s determined by the relative proportions of each solute distributed between a
moving fluid stream, which is called the mobile phase, in addition the stationary phase which
could join the mobile phase. The mobile phase is represented in the form of either a gas or a
liquid, whereas the stationary phase is represented in the form of either a liquid or solid.
Aim
Undertake chromatographic techniques to identify components in mixtures.
Key words
Mobile phase - the liquid that flows through the stationary phase.
Stationary phase – what the mixture is supported on (chromatography paper).
Chromatogram – the resulting piece of chromatography paper or plate.
Solvent – the liquid which scientists use for the mobile phase.
Polar – molecules which have an uneven distribution of electrons.
Solution - a mixture of components
Factors that affect chromatography (Shiken, n.d.)
1. Polarity – the rate a compound travels (how far it travels) up the chromatography paper
and is separated depends on the polarity. Polar molecules are more attracted to polar
solvents, so different compounds would move further up the chromatography paper if a
polar solvent was used as opposed to a non-polar solvent. (BBC Bitesize, n.d.)
2. Solvent – the type of solvent can reflect on how the compounds get separated while
going up the chromatography paper.
3. Temperature – temperature can have an influence on the R f value at the end of a
chromatography experiment, this is because if the temperature starts to increase the
process will become faster. (Thermo Fisher Scientific, 2016)
4. Solubility – the higher the solubility in the mobile phase, the faster the different
compounds will move up the chromatography paper. (Khan Academy, n.d.)
5. Absorption – the Higher the adsorption in the stationary phase, the slower the different
compounds will move up the chromatography paper. (Khan Academy, n.d.)
How is separation achieved in by differences in polarity and solubility of substances
Components within a mixture are separated in a column based on their attraction to the
mobile phase. This means that of the components have different polarities and a mobile
phase with a specific polarity is used, one component will move through the column faster
than the other. Since molecules of the same compound tend to move together, the mixture is
split into separate bands withing the column. (Chemistry LibreTexts, 2020)
Differences between paper chromatography and thin layer chromatography
The main difference between paper chromatography and thin layer chromatography is that
the principle in thin layer chromatography is based on absorption, while the principle in paper
chromatography is based on partition (when a solute is distributed between two phases in a
separation process). Another big distinction between thin layer chromatography and paper
chromatography is that paper chromatography uses a type of filter paper whereas thin layer
chromatography uses a glass plate coated with silica gel. (Auriga Research, 2021)
Paper chromatography employs a uniform absorbent paper as the stationary phase, and liquid
solvent or solvent mixture as the mobile phase. (chemguide.co.uk, n.d.)
Paper Chromatography
LEARNER ASSESSMENT SUBMISSION AND DECLARATION
, Paper chromatography is one of the many chromatographic techniques, it separates mixtures
in order to determine its components within that mixture. It’s mostly used to separate
chlorophyll, amino acids, and many more. Paper chromatography uses a very uniform
absorbent paper which acts as a solid supporting material which has small water molecules in
its pores, these function as a stationary phase wile ethanol, methanol, propanone, etc act as
the mobile phase. The mobile phase flows through the stationary phase and carries the
different components of the mixture with it (different components travel at different rates).
(chemguide, n.d.)
Extracted ink
This type of paper chromatography is used to separate and identify the different components
within a mixture, based on how far they travel along the chromatography paper. By doing this
we can determine the components’ different chemical properties and identify what their
“presence” is within the mixture (e.g. what colours make up the colour green).
Aim
Separate and identify the different components of a mixture within a coloured ink.
Equipment
1. Chromatography paper
2. Pencil
3. Beaker
4. Distilled water
5. Ink
6. Glass rod
7. Paper clip
8. Ruler
9. Pencil
10.Capillary tube
Method (Study Mind, 2023)
1. Using a pencil draw a line onto the chromatography paper approximately 1cm from the
bottom of the paper, this is the line where the inks will be placed. Do not use a pen as
pens aren’t soluble so the ink of the pen would also move along with the solvent.
2. Add the inks spots onto the pencil line on the chromatography paper, as far apart from
each other as possible so they won’t spread onto each other, and make sure that the
spots have a similar size. Making sure you add the different inks with different capillary
tubes, so the inks won’t mix with each other.
3. Put a small amount of distilled water into a beaker and then place the chromatography
paper onto the said beaker, making sure the distilled water sits below the pencil line
you drew a few minutes earlier.
4. Wait a few minutes until all the solvents have travelled upwards, when the solvent is
slowly travelling upwards, the different components of the ink will travel at different
rates, showing different coloured spots.
5. Once done, allow the paper to dry and calculate the R f value.
Risk assessment
Hazards Possible harm Precaution
Toxic solvents irritation or burn of the skin Wear gloves
irritation of the eyes Wear goggles
LEARNER ASSESSMENT SUBMISSION AND DECLARATION
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