Chromatography Lab Questions?

Question

Okay. I don't get this at all. We did a lab on chromatography with ink and water, and spinach (more along the lines of chlorophyll)and acetone. We then were presented with some lab questions (data analysis):

In both cases, which moved more quickly through the chromatography paper, the solute (ink or spinach) or the solvent (water or acetone)? Why?

They expected us to measure the levels of water and acetone on the strip of c. paper after it dried, but I can't see any water/acetone stains, only the ink/spinach.

2. How many bands of color were on the spinach chromotogram?
I only have 2, partially because instead of grinding the spinach and stuff, we just used a penny and rolled over it. Just to confirm, are these chlorophyll a and chlorophyll b?

4. Suggest a hypothesis explaining the change of color that often occurs when a leaf dies

5. Suggest a hypothesis explaining why a leaf changes color in the fall/autumn.

Okay... but we only had two colors on the spinach one! Help please?

Answer 1

Well, chromotography paper is polar, which is why it is used to test polarity of pigments. If you ended up with two green lines on your paper, then they are most likely Chlorophyll a and b. You probably didn't get any Xanthophyll or Carotene because I don't believe spinach contains much of either one of these pigments.



The acetone/water that you used is a solvent used as a traveling mechanism for the pigments or ink on the paper. The more nonpolar the molecule the higher it will travel up the chromotography paper, following the acetone.



Because chromotography paper is polar, it tends to have an attraction to other polar molecules. This is why polar pigments will stay closer to the beginning point on the c. paper rather than traveling, they are attracted more to the paper than the acetone.



As for fall when the leaves change color: The process of photosynthesis steadily degrades the supply of chlorophylls when the temperatures drop in fall or autumn.



Anthocyanin pigments produce reds and purple colors, though they are not always present in the leaves but are produced in the foliage in late summer when sugars are trapped in the leaves after the process of abscission begins.



This change in color is basically just a result from shorter days and longer nights in cool weather.

Answer 2

Paper Chromatography Lab Answers

Answer 3

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RE:

Chromatography Lab Questions?

Okay. I don't get this at all. We did a lab on chromatography with ink and water, and spinach (more along the lines of chlorophyll)and acetone. We then were presented with some lab questions (data analysis):



In both cases, which moved more quickly through the chromatography paper, the solute...

Answer 4

Youliya has a good definition of chromatography, but it doesn't really explain clearly how you can use it to identify substances. The preferred way to use chromatography to identify an unknown requires you to have a pretty good idea of what your unknown may be. Assuming you are doing TLC, you would run one spot of your unknown alongside one spot of the substance that you think it might be. If they are the same substance, they will travel the same distance on the plate. Usually you will run a few spots of possibilities alongside one spot of your unknown to give you a few choices. The other way would be to run your unknown, measure and calculate your Rf value, and then compare it to tabulated data. This is a bit more challenging, because it requires you to find a table of Rf values that matches up with your solvent mixture. Also, there are a LOT of compounds that will have the same, or very close to the same Rf values. I would not consider this method to be as reliable as a direct visual comparison.

Answer 5

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No of course it would not change the Rf Value, since the rf is the retardation factor (Rf) and is defined as the ratio of the distance traveled by the center of a spot to the distance traveled by the solvent front so changing the length by any factor will not affect the Rf