Monday, April 6, 2009

Macro-scale examples of chemical principles

I like macro-scale examples of chemical principles. Here's two I've noticed recently.

I was very slowly pouring popcorn into a pot with a little bit of oil. The kernels did not distribute themselves randomly but instead formed some long chain aggregations because, apparently, the oil made them more likely to stick to each other than to stand alone. This kind of aggregation occurs frequently at the molecular scale when some molecule has an affinity for itself.

This is wheelbarrow chromatography. During a rain, water and leaves fell into this wheelbarrow. Notice that the leaves and the stems separated; apparently the stems are lighter than water and the leaves are heavier. This sort of "phase separation" trick is frequently used by chemists to isolate one type of molecule from another in a complex mixture. Sometimes the gradient of separation might be variable density as in this example, but other times it might be hydrophobicity or affinity to an antibody or many other types of clever chemical separations known generically as "chromatography". Note that the stems clustered. Like the popcorn above, apparently there is some inter-stem cohesion force that results in aggregation as occurs in many chemical solutions.

No comments: