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NOVA Online: Hot Science/Chemical Residue
Chroma preparation

Color Separation Activity

Take a page of newspaper and cut off the top or bottom margins—don't cut anything with type on it. The strips of paper should be about an inch wide and about six inches long. Fold the strips in half, lengthwise.

Next, pour two tablespoons of water into a glass, followed by two tablespoons of rubbing alcohol. Stir them together.

In a spoon, mix some drops of blue and red food coloring together until you have dark purple.

Now back to your paper strips. Dip a paintbrush, or toothpick, into the spoon, and paint a thin stripe of purple on one of the paper strips. The stripe of purple should be about 2 inches from one end. One a second paper strip, paint a thin stripe of green food coloring. Take the green food coloring straight from the container, and don't mix it with any other color.

Drape your paper strips over the side of the glass. The strips of paper should be positioned so that the stripes of purple and green are just above the liquid. Tape the far end of the paper strips to the side of the glass so they stay in place. Let everything sit for 20 minutes.

What happens?

Note: You can do this same experiment using water-based color markers instead of using food coloring. We suggest you use a black marker on one strip, and a green marker on the second strip. You can also use a coffee filter instead of newspaper strips. Twist one end of the filter and let that be the end that sits in the water-alcohol mixture. Paint your stripe of color just above where the twist begins to unfold.



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