Paper Chromatography Lab Report

The chromatography paper is a very long molecule (a polymer) in which thousands of rings of six atoms are covalently bonded together into long chains which form tiny tubes within the paper. The water molecule has been spilt leaving oxygen between each ring The long chains are held together by side-to-side hydrogen bonding(O-H) between the chains, so there is also weak dipole-dipole moment. These side by side long chains are called sheets of cellulose. The sheets are held one on top of the other by Van der Waals forces. The geometry of the short, carbon-hydrogen bonds minimizes the distance between layers and, therefore, Van der Waals forces are maximized. The paper has polar and nonpolar parts; it has a strong affinity to itself and materials

As the isopropanol travels up the paper, due to the capillary action which is caused by the greater attraction of the solvent molecules to the surface of the chromatography paper then the intermolecular bonding between the solvent atoms. The solvent will hydrogen bond with the paper, the slightly negative oxygen of the paper will bond with the slightly positive Hydrogen of the solvent, and the slightly negative oxygen of the solvent will bond with the positive Hydrogen of the paper. As the solvent starts to move past the pigment, some of its molecules are sucked toward the surface of the paper and stick there temporarily before being pulled back again into the liquid they came from. This exchange of molecules between the surface of the paper and the solvent is adhesive effect called adsorption. The liquid's molecules will stick fast (adhesive) to the paper surface and also to each other (cohesive), so that each molecule pulls the next one along. The capillary action only occurs when the adhesive forces; attraction between the solvent and paper molecules are stronger than the cohesive forces, which is the intermolecular attraction between the solvent

This should not have happened because it changed the Rf value. Instead of moving up the paper, if the dotted line touches the solvent, the pigment would dissolve and move down the paper to the solvent. Since all of our trials for the 50% concentration was done on the same paper, it affected all the trails. For next time, do each trail on a different piece of chromatography paper.

Regular water was used instead of distilled.

During the experiment of the 50% concentration of isopropanol, the chromatography paper touched the walls of the graph. The experiment was repeated a 2nd with the 50% concentration but again the paper touch the glass walls. This is not good, because the solvent has the potential to attract to the glass. This results to inaccurate data because the pigment would be travelling towards the side of the paper and the Rf value would change.

Conclusion: The pink pigment solubility decreases as the concentration of isopropanol solvent decreases. The orange pigment solubility increases as the concentration of isopropanol decreases.

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