These two experiments are variations on the same
theme - using a solvent (in this case, water) to separate out the different
portions of a solute (e.g., ink particles or food coloring particles). The
principle is the same in all three cases. At the molecular level, smaller,
hydrophilic molecules migrate faster through the paper. Hydrophilic means a
"water-loving" substance, as opposed to hydrophobic compounds which
are not soluble in water. As well, molecules which are bigger (have a larger
mass) move slower along the paper. So the colors left closest to the original
start point are made of heavier molecules than those which move further away.
Coffee Filter Chromatography
- glasses or clear plastic cups
- coffee filters
- really cheap markers
- 1) Put about 1 cm of water into the bottom of the
- 2) Cut a rectangular piece of the coffee filter.
- 3) Holding the filter paper outside the glass, use
the pencil to mark a line on the filter just above the waterline on the
- 4) Take a cheap marker and put a SMALL dot of color
on the marked line.
- 5) Place the filter paper into the glass, so that
the marker dot is just above the water line.
- 6) Let it sit for 5-10 minutes.
- 1 square of paper towel
- clear plastic cup
- liquid food coloring
- scotch tape
- 1) Cut a strip of paper towel about an inch wide and
about as long as the cup is tall.
- 2) Tape one end of the strip to the pencil.
- 3) Place a drop of food coloring about an inch from
the opposite end of the strip.
- 4) Pour about 1/4 of an inch of water into the cup.
- 5) Balance the pencil on top of the cup so that the
paper hangs down into the water, but the drop of coloring must be above the
- 6) Wait until the water soaks the towel almost to
the pencil. Remove and set on a paper towel to dry and be observed.
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