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March 20, 2005
I'm still too stuffed from an Iranian New Year (Nowruz) feast to do much blogging tonight, or much of anything else. (And eid-e shoma mobarakh to any of my Farsi-speaking readers, while we're on the subject.)
I hope to be moving around well enough tomorrow to finish up a reaction I did on Friday, an old-fashioned zinc metal reduction. Doing that kind of chemistry really makes me feel a connection to the 19th century. Those folks would have understood instantly what I was up to last week, stirring zinc powder in a flask with some dilute hydrochloric acid and washing it off.
That's how you make activated zinc, and that's how people have been doing it for well over a hundred years. On long storage, it (like all the other reasonably active metals) forms an inert coating of oxide on its surface. That's all very well for something like stainless steel - in fact, that's exactly how it remains stainless - but it really interferes with other metal-surface reactions. A quick etching with acid freshens the stuff right up.
Metals that are more active than zinc (sodium, say) form oxide coatings even faster - while you watch, basically. Those metals tend to come in chunks, since they have the consistency of cold butter. Zinc you can buy as a fine powder, but sodium won't put up with being milled (although you can buy it as sort of a fine sand, if you so desire.) To get a fresh surface for metals like that, you can just cut off a fresh hunk and get it in the reaction quickly before it clouds over again. (Don't do it like this, though!)
My reaction was done in straight acetic acid, another nostril-flaring old favorite. When I worked it up partway on Friday, it appeared to have done what I wanted it to, which goes to show how reactions like this become classics in the first place.
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