Chromatography and Gravity

Chromatography: Is Black Marker Really Black?

The very important scientific technique of chromatography (separation of colors or parts in a mixture) can easily be introduced to kids by testing whether black is it's own color, or a combination of many.

1. Cut strips of either coffee filters or paper towels (I used both)
2. Have kids draw a line with a black washable/non-permanent marker. I used crayola. Make sure the line is at least a little higher up than the edge.
3. Place strip in water. Make sure you do not immediately submerge the marker line.
4. Watch as the water is absorbed and travels up the paper. What happens when it reaches the marker? The colors begin to separate. The color black is actually a combination of many colors (ROYGBIV). These colors travel up the paper at different speeds. With our markers, the separation of blue and red was clearly visible, with red moving further up the paper than blue.

Depending on age and curiosity of kids, you can go deeper into explaining this process, why it happens, and what it is used for in science and forensics. Talk about chromatography paper and other professional equipment. Usually other solvents are used instead of water, like rubbing alcohol or other liquid chemicals.. many of which would probably produce better results than our run. Or keep it simple- black is actually a mixture of many colors and an simple experiment can prove that to us. I also used a "mystery ink" which nothing happened to when placed in water... I had kids compare and deduce why. Some thought it was a different paper or water or technique, but eventually (and some quicker than others) realized this was a permanent marker and the markers we used were water-based.

Few tips:

• water travels up paper towels faster than coffee filter, obviously. Keep that in mind for impatient kids
• If you dunk the marker line into the water immediately, the experiment won't work. Boys especially didn't listen to directions and did this on their first try (see some in 2nd photo below)
• The steadier and still and longer you hold your paper upright in the water, the better results and better separation of colors you will get.
• If for some reason the water is taking a long time to reach the marker (most likely because a child put it too far up) you can help it along... don't submerge the line, but slowly dip the strip further into the water to speed up the process.

              

Gravity

I did a few simple gravity demonstrations. First, I asked my kids if they could explain to me what happens when a ball is thrown up in the air. Why does it fall to the ground? Why do all things we throw fall to the ground? Is there a name for this process? Is there anywhere we don't experience gravity?

Then I used simple items: book, feather, piece of computer paper (flat), crumpled up paper, small ball..etc to test which items fall faster to the floor and why? (weight and/or surface area)

Second experiment was learning how water travels from high places to low places because of gravity. We learned about a special tool, a siphon. When filled with water completely, you can place one end of the siphon in a bucket of water and the other end in an empty bucket of water (at a lower elevation than the full bucket).  Water will move from the full bucket into the empty bucket. We don't have our fish tanks yet but I spent time explaining that the siphon is used often during water changes for very large tanks- it is much easier than scooping water out!

Having two cups or buckets of the same size would be much easier. When the cup at the bottom was full of water, we stopped each end of the siphon simultaneously (by putting our thumb over it). Then we either poured out the bottom bucket or switched the places of the two buckets. Then put the siphon back into position and released our fingers. If the siphon is not completely filled with water at all times the process won't work and you'll have to stop and refill the siphon. The end that is pulling the water needs to be submerged in the water the whole time. At the other end, we held it a little above the cup so that everyone could see the water coming out.