I am attempting the 2016 Canadian Chemistry Contest Part A, and one of the questions concerns the WHMIS symbols and whether a compound is an oxidizer or not.

The correct answer is that ethanol would not require a WHMIS oxidizer symbol. However, I am confused as to why ethanol is not an oxidizer when compounds such as potassium permanganate and nitric acid are when all of them contain oxygen.

  • 2
    $\begingroup$ As noted in the answers, just because a compound contains an oxygen atom does not mean that it will readily give it up to oxidize another compound. Ethanol is pretty stable as it is and would only oxidize pretty strong reducing agents, so it does not warrant a hazard specification. The best example of a compound that is mostly oxygen (by weight) but rarely considered to be an oxidizer is water. $\endgroup$
    – airhuff
    Jul 9 '17 at 22:49
  • $\begingroup$ Ethanol does warrant a hazard specification, just not the one for an oxidizer. It's (in)flammable. $\endgroup$ Jul 10 '17 at 1:27
  • $\begingroup$ Airhuff has pointed this out perfectly. In addition, do check out the wikipedia page about redox reactions. It'll help you get a good deal of grip on what oxidation and reduction is. $\endgroup$ Jul 10 '17 at 16:46

For something to be an oxidiser. It must be capable of being reduced. The presence of oxygen is no particular indicator of the oxidising ability of a given species.

In potassium permanganate, manganese is in its +7 oxidation state (a very high oxidation state), consequently it is a good oxidant agent as it is able to gain electrons, causing oxidation of another species and itself being reduced.

In ethanol, there isn't the same possibility for reduction as the molecule is already in its lowest oxidation state. Even ethanal (an oxidation level up) isn't particularly oxidising (despite being able to accept electrons and become formally reduced).

  • $\begingroup$ Imho, the lowest oxidation state for a $\ce{C2}$ compound would be ethane and the lowest for carbon is methane. Ethanol is slightly oxidised (but not a lot). $\endgroup$
    – Jan
    Jul 10 '17 at 7:21

That a compound qualifies as an oxidizer under regulation is not bound to the presence of oxygen in that material, rather to either its innate ability to decompose easily under liberation of oxygen, or to yield compounds that itself liberate oxygen. Sometimes, oxidizers are simultaneously known as explosives (like peroxides). Since WHMIS is a Canadian system, details may be found either in English or French.

WHMIS/SIMDUT is to be seen in the context of the GHS system (English, French) by the UN/ONU. Note that not all oxidizing agents (in the perspective of a chemist), like Fluorine, or Chlorine (ref) need (yet) to carry the corresponding pictogram (ref) of an oxidizer. (It may be, however, that they are labeled with other pictograms, independently.)


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