Chromatography, Lab Report Example

Purpose

The purpose of this experiment is to identify an unknown dye in a mixture based on a difference in chemical properties between the solution and the chromatography paper. The compounds that have the highest degree of solubility will travel the furthest on the chromatography paper, while the compounds that have the least solubility will remain closest to the solution at the bottom of the chromatography paper. Compounds that are not soluble at all will remain in the area in which the mixture has been placed. This method will be used to determine the identity of pens based on their ink source.

Procedure

 Paper chromatography was used to separate the dyes that are contained in the ink of two different pens. The separation of dyes were first determined by testing several variables for the dye mixture, including water, salt water, and alcohol. This was used to demonstrate the best mobile phase for the dye. Next, previously collected data regarding R_fvalues retrieved using 5% sodium chloride solution will be used in conjunction with this newly generated experimental data to determine the identity of each of the two pens that are being tested.

After immersing the chromatography paper in the mobile phase solution, the solvent front will be marked. After the pen ink has been run, it will be allowed to dry and the distance travelled between the solvent front and the dye will be determined. This procedure was repeated for all three mobile phases and the R_f was calculated for each chromatographic spot.
Data

Chromatographic Data Using Water for Pen B

 Chromatographic Data Using Water for Pen BB

 Chromatographic Data Using 5% NaCl for B

 Chromatographic Data Using 5% NaCl for BB

Chromatographic Data Using 5% Isopropanol for B

Chromatographic Data Using 5% Isopropanol for BB

Calculations

Chromatographic Data Using Water for Pen B

RF = 6.4 cm/6.4 cm = 1

Chromatographic Data Using Water for Pen BB

RF = 6.4 cm/6.4 cm = 1

Chromatographic Data Using 5% NaCl for B

RF = 8.7 cm/8.7 cm = 1

Chromatographic Data Using 5% NaCl for BB

RF = 8.5 cm/8.5 cm = 1

Chromatographic Data Using 5% Isopropanol for B

RF = 0.4 cm/7.9 cm = 0.344

Chromatographic Data Using 5% Isopropanol for BB

RF = 6.3 cm/6.3 cm = 1

Results

 The best mobile phase for the pen ink was the 5% isopropanol, which is demonstrated by the fact that one of the spots travel the furthest. In addition, the results indicated that pen BB is made up of only one type of ink because it only has one spot. On the other hand, pen B made two dots on the chromatography paper, indicating that it was made up of two different types of ink. Therefore, a difference between the two pens can be determined based on the type of ink contained within the pen and how far it travels.

Discussion Questions

The best mobile phase for the separation of both pens is the 5% Isopropanol. While only one spot was observed for the BB pen in this solution, it was in this medium that the ink travelled the furthest. In addition, this was the only medium in which the B pen had two distinct spots. It is likely that the experiment should be repeated using yet another kind of chemical for the mobile phase for the BB pen, because it is possible that there is more than one type of ink used in this pen, but it has not resolved.

The Rf value for the B pen in the 5% NaCl solution was 1, and the spot traveled 8.7 cm. The Rf value for the BB pen in the 5% NaCl solution was 1, and the spot travelled 8.5 cm. Pens B and BB were chosen because they demonstrated the same Rf properties as the unknowns that were tested on the chromatography paper when the experiment was completed one year prior.

For both pens, I believe that the errors made were systematic because it appears that the mobile phase solution was not sufficient for the BB pen to allow the ink to separate. For the B pen, it is likely that if an error was made it was random due to the measurements related to human error. This error could be alleviated if the experiment were repeated three times and averaged.

A small round dot will give a more precise Rf value because it is easier to determine where the center of the dot is.

This experiment could be completed at home using a small straw as the chromatography paper and rubbing alcohol as the mobile phase. The ink will be separated into different parts of the small straw and the Rf could still be calculated using the distance the ink travels.