Jennifer Kazanciyan helps honors chemistry students at T.C. WIlliams solve a mystery through chromatography, the separation of black into different colors.
Photo by Shirley Ruhe.
"I need to talk to you about something," Jennifer Kazanciyan tells her honors chemistry students at the beginning of Wednesday's lab at T.C. Williams High School. Their faces turn somber.
"As you know, we have a lot of sensitive equipment and expensive chemicals in our lab. One of the bottles of silver nitrate, which is very expensive at $1,000 a bottle, went missing. A ransom note was left behind. But the halls are full of cameras, so we could tell which two students were in the room when it went missing. She continued, "We searched their lockers. But all we found were two black pens that could have been used to write the note."
Kazanciyan shows them a chromatogram of the ink from the ransom note. "You can figure out which of the black pens was used to write the note through chromatography, which is the separation of black into different colors."
One of the students surmises, "so this is our lab today, right?"
Another pipes up, “did this really happen?"
"Not that I know of," she replies with a smile.
Kazanciyan hands each student two 10 cm strips of chromatography paper. "After you have your paper, move back to the lab." Twenty five students sort themselves into four lab groups.
The first step is to draw a line in pencil approximately 1 cm from the bottom of both strips. They read the directions. "Using the marker, place a small dot in the center of the line and repeat with the second strip and the second marker."
"Now we pour 10 ml of water into each beaker. How do we know how much water when there isn't a measure?" One enterprising student says, "Wait a minute we have a 10 ml measure over here." They turn on the water to a trickle and quickly fill the narrow cylinder to the top. "There you go," A group "yeah" as the water reaches the top without spilling over.
"Who volunteers the first strip? We're supposed to put it in the beaker without touching the bottom. "
"Just a minute, which is which? Make your dot bigger."
The first strip starts to turn a blue, "I think it's teal color. Look at the other one. It is green and blue and look, it is yellowish at the bottom. We're supposed to measure the distance of the different colors as the water is absorbed up the strip."
"This looks more like the pen of the person who took the silver nitrate," a students conjectures, pointing to the second beaker. "Look. This has a lot more colors. In the sample Ms. Kazanciyan posted, the marker he used has a lot more colors."
This was the fun part. Their worksheet got harder with questions like: what is the molarity of this solution (include significant figures and units)? Is the ink in the markers a homogeneous mixture, a heterogeneous mixture or a pure substance? Do you think your solute is ionic, polar covalent or non polar covalent?
Kazanciyan says she never thought she would be a teacher. She always liked math and science but got a degree in chemical engineering. "Then I went to law school and I did that for a while." But she said she had always felt strongly about science and that people should know. So she enrolled in Virginia's career switcher program designed to fill shortages in critical areas. Now she teaches chemistry and physics while dreaming up interesting and challenging problems such as today's decrypting exercise using special ink and paper. One student says to the other, "I mean I really believed her story."