martinzoo

What if molecules cannot be separated by filtration OR evaporation?

Another technique you can use to separate mixtures is CHROMATOGRAPHY. It is based on the fact that different molecules stick to each other in different ways. In Greek, the word chromatography means to write with color. This technique was so named because it was originally used to separate colored compounds.

In order to show GB chromatography we did a simple activity. It’s called paper chromatography. It will show him that ink is really a mixture of several dye colors. Each of the individual ink colors can be separated from each other using this technique.

To set up the activity, I got an old shoe box. Why do we have so many of these laying around? And why do they ALWAYS fall on my head when I try to get them off the closet shelf? ….But I digress…. We then cut three long strips, about 5 inches, from a coffee filter. We taped them to the top of the box, like in the picture below.

Then we took three petri dishes and filled them with alcohol. Next, we took three ink pens, a red one, a black one, and a blue one. We removed the ink cartridge from the pens, cut them in half, and swirled the open end in the alcohol to color it. I was worried that we’d be getting ink all over the place, but surprisingly it was not easy to get the ink to flow out of the cartridge. So don’t have worries on that front.

This is what the alcohol looked like after the swirling, and whirling, and do-si-dos.

Then we put the petri dishes in the shoe box just under the filter papers. It’s ok for them to touch the bottom of the petri dishes, but don’t let them touch the sides or it will stop the flow of the color. This is what we got after one hour. You can see that red is a much faster moving dye.

We let the project sit for 24 hours and this is what we got. The red paper basically only showed the red and yellow colors. The black was the most interesting. It’s hard to see in the photo, but on the paper you could see a deep purple at the base, then blue color, and at the top was a barely discernible line that showed red and yellow. We had very similar, but much less dramatic results with the blue ink. In the photo, you can see a bit of the red and yellow colors on the blue paper.

We did a similar experiment to this last year as a Christmas project. And I think we’ll do that again early next week. In it, we used magic markers and we shaped the filter paper like Christmas light bulbs. We hung it in the kitchen window and with the sunlight streaming through the papers, it was SO beautiful.