Monday, October 10, 2005

Help!

I'm hoping someone knows the answer to this problem I am having.

I am doing an experiment with my 2nd graders where we are trying to extract the red, yellow and orange colors out of leaves. So far we've been able to get only yellows. I have tried nearly everything I can think of, and even consulted two chemistry professors, both of whom say I am doing it right.

Here are the steps we do:

1. Tear the leaf into tiny pieces
2. Using the edge of a rock, cut and rip the pieces into even smaller pieces
3. Place all pieces into a cup and add acetone, stir thorougly
4. Using a q-tip, dab the resulting green liquid onto a piece of coffee filter
5. Dip the coffee filter into rubbing alcohol, just barely gettiing into the dab of green liquid.

Variations I have tried:

- different leaves. I've used spinach, lettuce, collard greens, as well as leaves off of local trees.
- differnet strengths of rubbing alcohol, from 71% to 90%
- different strengths of acetone. While I haven't measured the mixture I have used about half acetone/half water all the way up to full strength.

Any ideas out there?

6 comments:

allen said...

What's the weight of leaves versus the weight of acetone? Too little in the way of leaves/too much acetone and you won't have a high enough concentration of the plant materials.

Also, how long are you running the experiment before giving up? Some plant materials aren't very mobile. It'll just take longer for them to propogate in the filter paper.

Finally, some plants don't have too much in the way of not-green pigments.

Here's a pretty good explanation along with some ideas about what might be going wrong:

http://www.itsjustabox.com/Sciencefair.htm

And this is the source of the link above:

http://www.lcresources.com/resources/reslinks.html

It's a more general liquid chromatography page including some links to professional organizations/discussion boards where you might be able to tap into some real experts.

Finally, there's this resource page:

http://www.chemistrycoach.com/Links%20to%20chemistry_experiments.htm

Do a "find" on "chromatography". There's several paper chromatgraphy links.

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The Science Goddess said...

First of all, don't use acetone. Nasty stuff.

Get some alcohol...ethanol (the drinking kind) is good, but isopropyl (rubbing) should also be fine.

Take your filter paper and lay the whole leaf across it. Use a quarter or ruler to crush the leaf onto the paper, making a line of pigment about an inch from the bottom of the paper.

Set the paper in a container with just a bit of alcohol in the bottom. Believe it or not, the less you use, the better results you will get.

I'd also consider using a dark green leaf (spinach)just to show that the reds, oranges, and yellows are in there, too.

Let me know if you want more info.

Mike in Texas said...

Allen,

Thanks for the links, I have them printed out and will look them over as soon as I can. I did look at one very quickly and tried the demonstration to seperate the colors from a maker, it makes a nice, quick display.

I've tried many different kinds of plants. This past week I've been using collard greens, which produce a very nice yellow.

I usually try to have about a 50/50 mix of plant material to a 50/50 mix of acetone/water. I'm going to try tomorrow to use water as the final mixture to seperate the colors on the strip. I usually have classes for 1 hours at a time, so we spend about 10 minutes mixing the leaves and acetone. We then let the test strips dry for several hours suspended upright.

allen said...

Looks like Science Goddess is the go-to on this one. Nothing like experience to ensure success.

Mike in Texas said...

With a name like "Science Goddess" she can't be wrong!