Chromatography techniques and applications

Chromatography

The purpose of this experiment is to observe/demonstrate one technique for separating mixtures or compounds we find in the world, and to understand the principles behind this technique. This knowledge and experience provides insights into the scientific method and some of the knowledge derived through this method of empirical investigation.

Much if not most of the world we interact with is made up of mixtures or compounds, from the clothes we wear to the drinks we imbibe to the fuels we put in out cars. Sometimes it becomes necessary to separate the individual constituent parts from each other and identify them and their quantities, for a variety of reasons. Chromatography is a broad set of techniques that enable this separation and identification by using combinations of stationary and moving phases to "stretch out" a substance in a manner that separates its constituent parts. This experiment demonstrates one specific type of chromatography using a filter paper, water, and a the test mixture whose parts will be variably attracted to the paper and the water, leading to different rates of progress through the filter paper. As the water is drawn through the paper, the parts of the text mixture more attracted to the paper will travel slower, while those more attracted to the water will travel faster.

Pre-Lab Question

The pre-lab question appears to be either, which student will get to the library first? or, which colors are mixtures, and what are they mixtures of? The answer to the first question is: the new kid will arrive at the library first. With fewer other people (molecules) attracted to him and blocking his way, he has a free course to travel (analogous to a substance more attracted to water). The popular student will have other people (molecules) clinging to him, slowing his progress (like a substance with strong attraction to the filter paper. When it comes to typical markers, one would expect that the orange, green, and purple markers are mixtures of red/yellow, blue/yellow, and blue/red dyes, respectively, although there are individual substances (i.e. not mixtures) that show as green or violet and so these might not be mixtures. Black might also be a mixture of these three primary colors in varying degrees, or simply contain a high concentration of a dark dye that appears black to the human eye in mot conditions.

Procedures

Artistic Patterns

1) Draw on the center of two pieces of filter paper, using only one color on one piece and two or three colors on another.

2) Using a medicine dropper, introduce water to the center of the pieces of paper, not saturating but adding water as necessary to continue driving capillary action.

3) Observe and record what happens to the marker lines when the water encounters them.

A Colorful Race

1) Draw a soft pencil line about a half-inch from the bottom of a strip of Chromatography paper, then using different markers place three dots on this line approximately one centimeter apart and not too close to the edge of the paper, either.