CHEM237 Lab 3 - Lab report for experiment 3 PDF

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Summary

Lab report for experiment 3...

Description

Results pigment

Rf value

Carotenes

0.99

Pheophytin B

0.90

Chlorophyll A

0.37

Chlorophyll B

0.24

Xanthophyll

0.22

Test Tube #

Pigments present

2

Carotenes, 1 unidentified

3

Pheophytin B, traces Carotenes,traces Pheophytin, 2 unidentified

4

Chlorophyll B,Xanthophyl

5

Traces of all

*the column chromatography didn’t go as planned: the solvent was poured too fast, disrupting the separation and making collection of pigment difficult and causing contamination. Tube 1 was spilled, so there is no data for it.

Discussion 1. The blended spinach is mixed with both water and a mixture of organic solvents, so that all possible compounds that exit the leaves get dissolved. NaCl is added to move the organic compounds to a different layer due to decreased solubility. Centrifugation separates fractions of different density, allowing for clear separation of the organic layer, whose density is lowest. The organic layer is then dried using a drying agent to remove any remaining water in the solution, since water is very polar and may interfere with separation in the column. The drying agent is then filtered out since it isn’t soluble and isn’t an compound of interest. The remaining solution is then exposed to air to remove as much of the solvent as possible and get a concentrated solution of pigments, which is important for good results in chromatography, especially TLC, since diluted spots are often

invisible. 2. Carotenes have the highest Rf values since they are the least polar, consisting solely of hydrocarbons. Chlorophylls and Pheophytin have very similar structures, but the presence of the magnesium ion makes chlorophylls significantly more polar, hence the lower Rf value. The difference in polarity between chlorophyll A and B is caused by the presence of an additional aldehyde group in chlorophyll B, which makes it more polar and causes lower Rf value. The lowest Rf value belongs to xanthophyll due to its high polarity caused by the presence of 2 hydroxyl groups. 3. Due to the poor execution of column chromatography it is impossible to point to specific examples. However, due to TLC’s and column chromatography’s being, in essence, the same process, the only potential differences could be caused by differing acidities/basicities of the adsorbents used. 4. Solvents utilized in this lab are hexanes, acetone, and the mixture of the two. Acetone is more polar than hexanes (which are hydrocarbons) due to the presence of the ketone group. The mixture provides a solvent whose polarity is in between the two, enabling a stepwise transition from nonpolar to polar solvents. In column chromatography, hexanes are used first, so as to separate the least polar species. Hexanes are followed by the hexane/mixture, and acetone is used last, to flush out the remaining polar molecules, which would otherwise move very slowly, if at all....