Paper Chromatography
Background Information:
Paper Chromatography is used for separating chemicals based on their different
properties (ex: solubility, size, mass, etc.) and thus, allows scientists to distinguish various
organic and inorganic materials. This technique is commonly used in crime scenes or in
laboratories to identify an unknown compound by comparing it to known compounds.
Paper Chromatography is divided into two phases: Stationary Phase
and Mobile Phase.
Stationary Phase describes the paper before the solvents start to move up and Mobile Phase is
when the solvents travels up the chromatography paper while carrying the solute (e.g.
pigments).
Objective:
In this experiment, we will observe black ink consists of other pigments and how different
pigments in black ink separate based on their solubility. Capillary action allows solvent to travel
up the paper and different pigments in black ink will separate based on their solubility. Pigment
that is more soluble in polar solvent will travel up the paper along with the solvent, but pigments
that are less soluble in polar solvent will travel more slowly because of their interaction with the
chromatography paper.
Materials Needed:
1. Chromatography Paper (White Paper Towels can be used as a substitute)
2. Solvents: must be polar (Ex: distilled water & rubbing alcohol)
3. Ruler
4. Pencil
5. 3 Black Ink Pens/ Markers
6. Cup (preparably clear, plastic cup but not necessary)
7. Tape
Procedure:
1. Preparing chromatography paper: Cut the paper towel: 2 cm by 15 cm. Then, measure 4
cm from one end and draw a line using a pencil and also a midline dividing the 4 cm line
you just drew (as shown in the picture below). This is the baseline.
It’s important to use
pencil
because lead will not dissolve in water, preventing experimental error in chemical
separation.
2. Using black ink pen or marker, draw a small dot at the cross section of two lines you
have drawn previously.
3. Preparing Solvent: Mix equal amounts of water and rubbing alcohol in the cup (height ~
2 cm). Rubbing alcohol by itself is also fine. Make sure the height of the solvent is less
than 4cm. (You don’t need large amounts of solvent, just a little bit as depicted in the
picture below).
