MadSci Network: Chemistry

Re: Balanced equation for the decomposition of acetone with Cu as a catalyst?

Date: Sat Mar 7 13:58:16 1998
Posted By: Jeremy Starr, Grad Student, Chemistry, California Institute of Technology
Area of science: Chemistry
ID: 888273142.Ch

Hi Steve,

	This is an interesting question. To help myself understand what you were
seeing I attempted to reproduce your results in the lab where I work. I
tried three or four times each with two pennies and was unable to cause the
glow that you observed. (I will get back to why I think my attempts didn't
	Here is what I think is happening: The hot penny is igniting the acetone
fumes mixed with air above the beaker and causing them to burn at the penny
surface. I suspect the reaction would work on almost any metal surface but
is more observable against the dark background of the penny (as opposed to
the light reflective background of a quarter which has a surface layer
composed of 75% copper according to the CRC handbook of chemistry and
physics 1989-90, pg B-35). I didn't find any examples of copper assisted
combustion, but it is certainly well known that some metals are better for
this kind of reaction than others (hence the expensive platinum and
palladium in catalytic converters rather than cheap copper!). The balanced
chemical equation for combustion of acetone is:

	4 O2(g) + 1 C3H6O(g) ---> 3 H2O(g) + 3 CO2(g) + heat.

As for my own experiments, my lab is quite drafty due to the ventilation
system we have so I think the acetone/air mixture outside the beaker was
too thin for ignition (demonstrating that the ventilation system is doing
the job it is supposed to do) and the mixture inside the beaker was too
rich. I am sure an open flame would be required under those conditions. I
also found that a penny cannot be directly heated to a temperature at which
it glows without it first melting into a glob of metal (which I infer from
your question is not what happens in your case). This is further evidence
that the glow you are seeing is the combustion reaction and not from the
temperature of the metal. 

I hope this information was helpful!


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