AP Chemistry
Paper Chromatography
Inv. #5
Completed for AP Chemistry
At
Iroquois High School
By:
Jill Chipman
On:
October 20,2008
Purpose
The purpose of this lab was to use chromatography to determine the ions present in an
unknown solution
Summary
Solvent was placed in a beaker and then covered with wax film. Tiny drops of Ni2+,
Cu2+, and Fe3+ were placed on a piece of chromatography paper. This paper was then
stapled into a cylinder and place in the beaker. Once the solvent came close to the top of
the paper, the paper was removed and allowed to dry, while the paper was still wet, the
solvent line was traced. The dry paper was then sprayed with NH3 solution and allowed
to dry (this allowed the Cu2+ to appear more clearly). Once the paper was dry it was then
sprayed with dimethylgloxime solution (this allowed the Ni2+ solution to turn pink). The
paper dried again. The spots on the paper were circled and a dot was placed in the middle
of each one. Rf values were calculated after measuring the distance the spot traveled
compared to the distance the solvent traveled.
1. Chromatography allows us to separate various components of a mixture based on
solubility. The colors and/or lengths of the components can then be used to identify
unknowns.
2. The Rf value of a component is a ratio of the distance traveled by the component to the
distance traveled by the solvent. It can be used to identify the parts of a mixture.
3. Partitioning which is the separation based on solubility differences, of compounds
between a moving and not-moving phase allows for the ions in the compound to be
continuously adsorbed and released into the solvent and travel up the paper. The
components travel at different speeds (due to the different forces of attraction) which
show the different components of the compound.
4.
Cu2+ + 4NH3
[Cu(NH3)4)]2
5. The solvent front should be marked immediately so that it does not dry, fade, or recede
and the distance can be measured accurately for use in calculating Rf values.
6. Rf = D component
D solvent
Rf = 32 mm
80 mm
Rf = .40
7. The ions in our unknown solution were: Fe3+, Cu2+, and Ni2+