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56 SCIPAD - BIG IDEAS - BOOK 1
THE NATURE OF MIXTURES
Chromatography - Separating a Mixture of Coloured Compounds
Chromatography (chroma - Greek for ‘colour’ and graphy meaning ‘words’ or ‘pictures’) is a
scientific technique used to separate a mixture of two or more coloured pigments, such as inks
and dyes. The pigments separate because they move at different rates through the paper. Smaller
and more soluble pigment particles move faster than larger, less soluble particles.
Separating a Mixture using Chromatography
Aim:		 To separate the different pigments in inks or dyes using paper chromatography.
Equipment: Inks from ballpoint pens, marker pens or food colouring, 250 mL beaker, strip of filter
paper, scissors, adhesive tape, pencil or ice-block stick, chromatography solution.
Method: 1. Cut a strip of filter paper that is long enough to reach the bottom of your beaker
and able to wrap around your pencil or ice-block stick.
2. Rule a line in pencil approximately 2 cm from the bottom of your piece of paper.
3. Fill your beaker with enough chromatography solution to fill your beaker to a depth
of 1 cm.
4. Place a dot of ink above the ruled line on your filter paper. You need to produce a
concentrated dot of ink so repeated applications may be necessary.
5. Suspend the strip of paper from the pencil or stick. You may need to use adhesive
tape to stop it from falling into the solution.
6. Wait to see what happens. It is important that you do not disturb the beaker. If the
solution comes in contact with the ink dot, the ink will run down into the solution,
rather than move up the filter paper.
Observations: 


1. Outline the origin of the term chromatography. 

2. Describe the type of mixtures that chromatography can separate. 


3. Explain why the pigments separate. 


4. Which pigments are carried the furthest by the solvent? 

Chromatography
solution
At the start At the end
Dot of ink
Solvent
solution
Filter paper
Various
pigments
from the ink
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