Paper chromatography demonstrates separation of colors from inks. While not part of the new requirements, it is relatively easy and safe. Then, I'll relate this to how you can use solvents to clean things, which leads nicely to a neat demonstration of using isopropyl alcohol to clean a sharpie marker from various things in the classroom.
- Coffee filter paper (or some other type of paper base)
- Wide bottles
- Variety of pens or markers, both permanent and not.
- Isopropyl alcohol
- Acetone (I got it from nail polish remover) (I didn't let students use this, I did demos myself)
- You need to use alcohol, if you only use water as the solvent, you don't see enough varying effects. Also, there is a large benefit to contrasting various fluids. Acetone is good, but I don't want to give it to students.
- You want some sort of wide-mouth bottle. If the bottle is too narrow, the paper will stick to the sides and it will mess up. You might not even be able to get the paper all the way down inside if it's a test tube and the walls are wet.
- Cut the strips thin, to minimize touching if you put multiple strips in at once. You don't want the strips to stick together inside, this will mess up the wicking. I have found that you don't need the strips to be completely flat, you can rub them on the edge of the table to get then flat enough. But I still don't see a perfect upward travel, the travel gets deflected to the sides still.
- Do not let the ink dots go underwater. This messes up the flow of liquid upward, and you won't get very good separations.
- I haven't tested how good it is to use one wide strip of paper and place multiple dots on it. I'd expect the main problems are forcing the liquid to go straight up (so that the dots don't mix), keeping the paper off the walls, away from other paper or itself, and the dots from submerging.
- I have found that students have a low success rate with this (at least without practice). It is a good idea to do this in advance, so that you can show what is is supposed to be like. Tape them to a sheet of paper so that you can easily pass them around. This is also a good demo for acetone as a solvent.