— Paper Chromatography Chemistry Question

This is a paper-chromatography identification experiment. Ammonia and water are provided as the carrying liquids. Students had to create an experiment using pieces of filter paper to observe a possible separation of the black ink dyes from each of the four pens provided. Situating the filter paper on or in provided beakers allowed the solvent front to rise, showing a possible separation.

Experimental Plan
The experimental plan needed to identify a way to use paper chromatography to investigate the inks in the various pens. Some detail about how to carry out the experiment – marking the filter paper above the liquid level, for example, was useful in this component of the exercise.

Observations and results:
Students needed to summarize observations about the chromatography experiment. Students who did an excellent job carried out more than one trial to verify results and included detail about separations. A table of probable observations includes,

An example of excellent student work:
Using Ammonia as solvent: - Pen 1: Different colors appear: orange, blue, green and purple - Pen 2: Solid black color only appears. - Pen 2 (again): Still shows only solid black color. - Pen 3: Different colors appear, but they are light: green, blue and purple - Pen 3 (again): Different colors appear again, darker than previous run. - Pen 4: Mark does not move, only black color appears. - Pen 4 (again): Mark does not move, only black color.

Using water as solvent – retry #2 and #4. - Pen 2: Solid black color only appears - Pen 4: No movement observed. - Pen 4 (again): No movement observed.

Conclusions:
Pen 1 is a mixture because different colored pigments are observed. Pen 2 is a compound because only one color is observed even though the ink moved along the filter paper. Pen 3 is a mixture because different colored pigments are observed. The pigments used are different than those used in Pen 1.
Pen 4 can not be determined in this experiment because no solvent was found that dissolved the ink. Based on the fact that separation of color is not observed, the ink might be a single compound.

An example of good student work:
Pen 1: Mulitple layers form. Fastest moving layer is light blue green. A darker blue-green is next and a purple color is the slowest. Pen 2: One dark black layer that doesn’t seem to move at all. One light black layer that moves slowly. One gray layer that moves faster. Pen 3: One black layer doesn’t move much. One light black layer that moves slowly. One blue-purple layer that doesn’t move at all. Pen 4: Black mark doesn’t move at all and remains dark black.

Conclusion: The pens with multiple layers in the paper chromatography were mixtures – in this case pens 1, 2 and 3. The pen with a single layer in the paper chromatography, pen 4, was a single compound.