experiment 9 : separation of a mixture by paper chromatography

EXPERIMENT 9 : SEPARATION OF A MIXTURE BY PAPER
CHROMATOGRAPHY
Objective : To separate , detect , and identify the
components of a mixture by using paper chromatography

Introduction
Paper chromatography is a method of
separating mixtures by using a piece of
absorbent paper. In this process, the
solution to be separated is placed on a
piece of dry filter paper. This is the
stationary phase. A solvent (the moving
phase) is allowed to travel across the
paper by capillary action. As the solvent
front moves, the components of the
mixture separate.

R f values
The distance traveled by a component of a spot with
respect to the distance traveled by the pure liquid is a
measure of that component's competitive affinities for
the stationary and mobile phases. We define the
component's Rf (retention factor) value I those terms:
For example, if one component of a mixture travelled 9.6
cm from the base line while the solvent had travelled
12.0 cm, then the Rf value for that component is:

Chemical Used
• Fe 3+ solution .
• Cu 2+ solution .
• Ni 2+ solution .
• Mixture ( 90% acetone
and 10% 6 M HCl .
• 15 M ammonia .
• Dimethylglyoxime.

Procedure
1. In a piece of chromatography filter paper draw 1 line 2 cm from
one of the longer edges. Mark the line with a pencil dot at six
places

2. Fill your capillary pipet by dipping the end into the solutions
of ions( Cu 2+ , Fe 3+ , and Ni 2+ ) , Known solution of the three
ions, and unknown solution . Allow the solution to rise by
capillary action.
3. Apply a single drop of the solutions in to the filter paper .

4. Pour the mixture in to a depth of 1 cm (about 20 mL) in
the bottom of a 600-mL beaker .
5. Fold the filter paper and staple to make a cylinder shape
as shown in the figure below and place it in the beaker.
6. Cover the beaker carefully with a watch glass. Do not
disturb the beaker while the chromatograms are developing
7 . When the solvent front has nearly reached the top of the
paper, carefully remove the watch glass and the paper. Place
the wet paper on the paper towel and immediately mark the
solvent front with a pencil. Allow the filter paper to dry.

Tips
•The 2-cm line should be above the surface of the liquid Be
certain that the spots on
•The paper are completely dry before you place the paper in
the beaker .
• Make sure that the paper does not touch the wall of the
beaker and that the bottom of the paper is resting in the
solution.

Observation:
1. Fe 3+ in water imparts a red-brown or rust color and thus will
produce a rust-colored band on the paper with out any
development. As shown im the figure below.
1. Fe 3+ Yellow
color

2. To detect the second ion (Cu 2+ ) :
IN THE HOOD, pour about 5 mL of 15 M ammonia into a clean,
shallow dish and rest the filter paper on the top of the dish. Do not
permit the paper to dip into the solution.
What color develops ? Blue spots
What ions dos this indicate ? Cu 2+
Cu 2+ is blue, the color is faint and not easily detected, especially
if copper is present in small amounts. In aqueous solution,
however, Cu 2+ reacts with NH 3 (from ammonium hydroxide) to
form a complex ion, [Cu(NH 3 ) 4 ] 2+ , which is deep blue and
therefore readily observed
Cu

3. To detect the third ion, dip a new piece of filter paper into
a solution of dimethylglyoxime; then, using the new piece as
a brush, paint the test filter paper.
What color develops ? Pink spot
What ions does this indicate ? Ni 2+
Ni

4. Analyze the paper , notice that the mixture contains
three spots that indicate the three ions, and the
unknown contains two spots .
Fe 3+
Trace Cu 2+
Cu 2+
Unknown (Fe 3+ &
Ni 2+ )
Unknown
(Fe 3+ , Cu 2+ &
Ni 2+ )
Ni 2+

5. Measure distances from the start line to the solvent front and
to the middle of each spot.(R f ) Write down results in
your work sheet.

• Understanding the results:
The number of the spots or bands tells
you how many compounds are in your
substance. Their color and the distance
they traveled might help you to identify
those compounds.

REPORT SHEET
1. Color of spots: Cu 2+ ________ Ni 2+ _________ Fe 3+ ___________
2. Ion requiring no development ___________
3. Ammonia develops a ___________ color.
4. The ion that causes the color of (3) is _________
5. Dimethylglyoxime develops a ______________ color.
6. The ion that causes the color of (5) is __________
7. Ring front distances for knowns are: solvent: _______ mm;
Cu 2+ _________ mm; Ni 2+ __________ mm ; Fe 3+ _________ mm.
8. R f values for knowns: Cu 2+ ________ ; Ni 2+ ________ ; Fe 3+ ________
9. Unknown label ________
10. Ring front distances for unknowns:
__________ mm ; __________ mm ; __________ mm.
11. R f values for unknowns:
____________ mm ; ____________ mm ; ____________ mm ; .
12. Ions present in unknown __________________