Only chemistry folks will truly appreciate this, but it’s funny so I’m posting it.

We had to grade a Chem 125 exam this evening, and one of the reactions they had to discuss was a redox reaction between tin(iv) (as the chloride salt solution) and cobalt metal, which produces (reduced) tin(ii) and (oxidised) cobalt(ii). The chloride ions are spectators, obviously. Well, a certain rather significant subset of the students apparently don’t understand the concepts of a net ionic equation and spectator ions. So we had a lot of students writing some sort of reaction that gave cobalt(ii) chloride as a product in aqueous solution.

Problem is, a significant fraction of these don’t write elemental symbols with particular care, which means their cobalt atoms look more like carbonyl (CO) ligands, or, in the case of elemental cobalt (Co), carbon monoxide (CO).

The observant reader can probably predict where this is about to go. Cobalt(ii) chloride, if written carelessly, looks like this:


Anyone remember the little segment of Square One Television, the great math series on PBS in the late 1980s, that was called Oops!, and “brought to you by erasers,” of course? Yeah, well, oops. Let’s just say that if these students - and the overwhelming majority of them are pre-med and engineering - ordered some of the above chemical, better known as phosgene gas, instead of cobalt(ii) chloride, or accidentally ingested some, well, I wouldn’t want to be anywhere in the immediate vicinity. Melting lungs are not a pretty sight, and in addition to hydrolysing to produce copious hydrochloric acid in the lungs, the other byproduct of aqueous phosgene decomposition is (drum roll please) … carbon monoxide.

Is anyone really surprised that phosgene was used by the Germans in World War I as a chemical agent?

I’m going to have to remind my students to be more attentive to their handwriting in the future. Then again, we did get a great laugh out of some of the rather preposterous answers to that test question. I didn’t know CO(s) had a +2 charge…then again, I didn’t know Ag3+ or Cl4- ions existed (or were good reducing agents!), either.

posted by Chris on 12 March 2003 at 0120 in school


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