Chemicals: 0. Avoid contact with the metal ion solutions, the eluting solvent, and the visualizing solution. Wear disposable gloves to touch your chromatogram after the elution occurs and for the remainder of the experiment. Do not breathe the vapors of the eluting solvent or the visualizing solution. Place the wet chromatogram on a paper towel, not directly on the laboratory bench. Use the visualizing solution only in the space provided by your instructor. Dispose of the gloves and chromatogram in the specified waste container after the experiment is finished.
Wash your hands thoroughly after contact with all solutions in this lab. Figure 4: Folded paper should look like this prior to developing the experiment. Figure 5: Measurement of distances used in the calculation of R f for a spot.
Paper Chromatography Lab by on Prezi
Place the chromatography paper and the used gloves in the waste container provided. The used eluting solution should already have been placed into another waste container. Note that two different waste containers are provide for this experiment so be sure to read the labels so you will use the correct one! Be sure to wash your hands thoroughly before leaving the laboratory. An unknown solution containing some of these cations will be identified by comparison to the R f values and colors of the stained spots of known solutions. Procedure Materials and Equipment Chemicals: 0. Preparation of the paper for chromatography Each pair of students should obtain a piece of filter paper with the dimensions shown in Figure 3.
Make sure the paper is clean and without tears or folds.
Use a pencil —not a pen—and a ruler to draw a line across the paper one cm from the long edge of the paper. You will spot the metal ion solutions on this line. Write your name in pencil in the upper left-hand corner of the paper. Use glass capillary tubes to spot the ions onto the paper. Solution is applied by lightly and quickly touching a capillary tube containing the solution to the line you drew on the paper. The spots should be between 5—8 mm in diameter. Spots larger than this will excessively spread out during the experiment and make analysis difficult.
Known 0. Starting on the left, mark the identity of the ion underneath each spot with a pencil; then spot each known ion carefully onto the line.
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Be careful to avoid contaminating the capillary tube with other ions and replace the capillary tubes back into the correct test tube. A test tube containing a known mixture of all five ions is also provided with a set of capillary tubes. Spot this mixture onto the line as well. Because this solution is more dilute than the single-ion known solutions, apply the known mixture three times, letting the spot dry between each application.
A heat lamp will help to dry the spot more quickly. Several unknowns are also provided in test tubes, along with capillary tubes. Your instructor will tell you which unknown should be used. The unknowns will contain between one and four cations, and are more dilute than the single-ion known solutions. The unknown will also need to be applied two and four times for the two trials, letting the spot dry between each application.
In case of error, you should spot the unknown in two places along the line so that two trials are available for analysis. Developing the chromatography paper Place a piece of tape along the upper right edge, as shown in Figure 3. Then form a cylinder by connecting the two short edges of the paper with the tape.
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Make sure the edges do not touch. The paper should look similar to Figure 4. Obtain 15 mL of the eluting solution. Carefully pour some of this solvent into a mL beaker and carefully swirl for a second or two. Caution: Do not breathe the vapors from this solution! Make sure that the level of the liquid will be below the spot line on the paper once the paper is placed in the developing chamber.
Place the paper cylinder into the beaker with the marked edge down. The spots should be above the level of the solvent. The paper should not be touching the sides of the beaker. Carefully cover the beaker with plastic wrap and place it in the hood for minutes. The solvent should start to move up the paper.
Once the beaker is covered, make sure it is level and do not disturb it during the development period. Your instructor may have an assignment for you to work on while you wait.
Visualization and analysis of the paper Once the development period is over, wear disposable gloves and remove the paper from the beaker. Latex gloves are available in the lab and nitrile gloves are available in the stockroom for people with Latex allergies.
What Is Chromatography?
Let any solvent drip back into the beaker, then remove the tape. Lay the chromatography paper on a paper towel and immediately mark the solvent front with a pencil. Pour the used eluting solvent into the waste container provided. Dry the paper under a heat lamp in the hood.
Caution: Do not breathe the vapors! Be careful not to burn the paper under the lamp. Once the paper is dry, bring it to the visualization station on the paper towel. Briefly dip the paper into the visualizing solution located in a shallow dish in the fume hood. Lift the paper out of the solution immediately and let any excess drip off at the station. Place the wet paper onto a dry paper towel and dry it under a heat lamp immediately, then carry it to your bench for analysis.
Find each known single-ion first and record the colors you observe. Some spots may fade over time, so record the colors while the paper is still wet. Measure the distance each spot moved, D, with a ruler. Measure to the center of each spot. Record your data in the data table. Measure the distance to the solvent front, F. The value of F should be approximately the same across the entire paper. Use these values to calculate the Rf for each ion. Make your measurements as shown in Figure 5.
separation of cations by paper chromatography
Each observed spot has its own R f value. Record your results in the data table. In the lane containing the mixture, find each ion and record the distance moved by each ion. The retention factor for a chemical during thin layer chromatography is a measure of how far it moves up the plate in response to the solvent movement. Since the absolute movement of the chemical depends on how far the solvent travels, you calculate retention factor values relative to the degree of solvent movement.
The retention factor for a chemical is the vertical distance moved by the chemical from the spot where it was originally applied to the plate, divided by the distance traveled by the solvent — measured from the same starting point. The thin layer chromatography plate itself can affect the retention factor value obtained for a given chemical. Thin layer chromatography plates can be coated with a variety of absorbent solids; most frequently silica or alumina. Since the retention factor is based on the relative affinity of the chemical for the absorbent compared to the solvent, changing the absorbent can greatly change the retention factor.
3: Paper Chromatography- Separation and Identification of Five Metal Cations (Experiment)
Also, the thickness and uniformity of the layer of absorbent can vary from plate to plate, especially if they are handmade. These factors can also change the retention factor value for chemicals. Since the solvent carries the chemical up the plate, the particular solvent used will also have a substantial impact on the retention factor value for the chemical.