Paper Chromatography: Separation of Cations and Dyes
To have become acquainted with chromatographic techniques as a method of separation and identification of substances Materials:
Evaporating dishes (2)
4 in. watch glasses (2)
Paper chromatography strips
12.5 cm Whatman filter paper 600 mL beaker
100 mL graduated cylinder
paper clips (3)
6 in glass stirring rod
0.5 M Cu(NO3)2
0.5 M Fe(NO3)3
0.5 M Ni(NO3)2
15. M NH3
Black felt-tip pen
The basis of this laboratory exercise was to become familiar with the method of separation known as chromatography. Chromatography is defined as a technique used by chemists to separate components of a mixture or solution. Chromatography is also the general name for a series of methods for separating mixtures by employing a system with a mobile and a stationary phase (1). The first chromatography occurred by allowing a solution of colors to flow down a column packed with an insoluble material such as starch, alumina or silica. Because different color bands appeared along the column, the process was called chromatography. Chromatography is used by chemists all across the world and many more chromatography have developed since the development of paper chromatography in 1943 (2). The mixture is dissolved in a fluid called the mobile phase, which carries it through a structure holding another material called the stationary phase. To identify an ion in a solution, by chromatographic means, the Rf value is used to determine it. The Rf value is a characteristic of a compound, the support, and the solvent used, and it serves to identify the constituents of a mixture. The Rf value is defined as the ratio of the distance traveled by the substance to the distance traveled by the solvent. In this laboratory exercise both the horizontal circular technique and the ascending strip technique were used. Rf of Cu = d Cu/ d s. (4).
There were two simple ways of performing this experiment: by circular horizontal chromatography or by ascending chromatography using paper strips. The two techniques should have been then compared in terms of time required, separation, and ease of identification. Make six capillary pipets by drawing out 6 mm glass tubing. The instructor demonstrated how this could be done, or the capillary tubes could have been obtained from the instructor. Obtain the unknowns and do not pour the chemicals down the drain. Dispose of them in the designated receptacles A.
Cut a wick about 1 cm wide on a piece of 12.5 cm Whatman No. 1 filter paper. Avoid touching the filter paper if your hands are oily. Trim about 1 cm from the end of the wick so that the filter paper will fit into the petri dish. Mark the center of the paper with a pencil dot. Place the cut filter paper on top of another piece of filter paper or a paper towel, which did serve as an absorbing pad. Using the following technique, “spot” the filter paper at the center on the pencil dot sequentially with 1 drop of each the known solutions, letting the spot dry completely between applications. Pour a small quantity of Cu2+ solution in a clean sample vial and fill your capillary pipet by dripping the end in the solution. Allow the solution to rise by capillary action. Withdraw the pipet and touch the inside of the vial with the tip of the pipet to remove the hanging drop. Spot the filter paper on the pencil dot by touching it with the capillary held perpendicular to the paper. Allow the solution to flow out of the capillary until a spot with a diameter of about 5 to 7 mm is obtained. Dry the filter paper in the air by waving it in the air. In the same process drop the Ni2+ and the Fe3+ solutions in. In the...
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