Wednesday, March 11, 2015

Black is black, right? Nope. (A Chromatography Experiment)

Because our color theory activity book was such a hit, I suspected a chromatography experiment would be as well. I was right.

My 9-year-old son and I both found this fascinating. 

I can think of loads of other adjectives to use to describe it too ... cheap, simple, fast, impressive ... heck, it was almost magical.

Clear Drinking Glass
Coffee Filter
Black Watercolor Marker
Rubbing Alcohol

1. Flatten and cut the coffee filter into a wide strip that's a little more than an inch across. Trim the ends to make a rectangle.

2. Tape one end around the middle of a pencil. Put the coffee filter pencil into your glass, so the top of the pencil ends rest on the rim of the glass and the filter hangs down into the bottom. Trim the coffee filter so it just touches the bottom of the glass. Remove.

3. Fill the glass with a 1/4-inch (or approximately 1 centimeter) of rubbing alcohol.

4. Draw a dot in the middle of the coffee filter strip about 2 centimeters (or a 1/2-inch) from the bottom. Your dot needs to be higher than the amount of alcohol in your cup.

Place the pencil back on top of the cup so the bottom of the coffee filter touches the alcohol in the glass. 

Watch what happens as the coffee filter wicks up the moisture. How does it impact the dot? 

My son's hypothesis was that the dot would totally disappear. When he saw the dot appearing to move up the paper, he thought he might be on to something.

The more we watched, the more the dot changed. The pigments in the watercolor ink began to separate. First, we saw green, then pink and purple and even some blue too. I reminded my son about how we make black paint from other colors of paint. "Oh yeah!" he exclaimed.

The rubbing alcohol initiated chromatography, which (in layman's terms) is the process of a liquid or gas changing a mixture into its components, in this case through absorption.

By the end of the night, our black ink had moved all the way up the coffee filter strip. What a cool experiment!

This wonderful activity came from Science Experiments for Kids.

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