Using Chromatography to Understand Marker Colors

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You would think that a black marker has black ink. And a green marker has green ink. But do they? That was the objective of this MEL Science chemistry project.

First we put put a nice big black dot in the middle of the filter paper. And it’s black. No doubts there.

Next, we put wet the cotton cylinder with our solvent. For this project, we used sodium hydrogen sulfate (NaHSO4). The marker ink is water-soluble so any aqueous solution should work, sometimes even water, but we used the acidic solution that came with the kit because, well, it came with the kit.

Then we put the cylinder right on top of the circle we drew earlier and let gravity take over. The solution will begin to soak into the dye and that’s where the magic happens.

The black dye is really several pigments mixed together. When the solution spills into the dye, the different pigments interact differently with the sodium hydrogen sulfate and the filter paper’s surface. Hence, the different pigments move at different speeds and that’s why we get the different colored rings.

Najwa then wanted to do the same thing using other markers. We grabbed a yellow highlighter and a green marker. Apparently highlighters work differently than markers. Nothing happened. But the green marker resulted in what should’ve been obvious — blue and yellow.

Chromatography is used to separate and analyze substances in complex mixtures or in a solution. The substances we analyze interact with two phases – stationary and mobile. According to their differences in structure, substances can interact with both phases in different ways. Thus, they separate and we can analyze them one by one, rather than in combination.

We did a second project which was less science and more artsy but it had to do with color. Tie-dye.

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