Platinum and Methanol
Name: Joanne J.
Date: 2001 - 2002
When a platinum wire is heated then place in a beaker
with methanol. The two never come into contact but after a bit there is
a small combustion, this small reaction keeps repeating it's self until
all the methanol is gone. With about a minute of time passing between
each reaction, what is the catalyst that causes the gas to combust, then
have to wait before another reaction occurs.
What you are witnessing is a catalytic oxidation of methanol to formaldehyde.
The catalyst is the hot surface of the platinum wire. The heat of combustion
of the methanol keeps the wire hot enough to do the job. The reaction cycles
because the methanol vapors in the reaction zone become depleted each tome
the "small combustion" occurs. When more vapor contacts the wire, the
Try this: Wind a piece of copper wire around a pencil to make a coil with a
straight piece sticking from one end. Bend the straight piece into a hook.
Heat the wire until it glows and then hang the hook onto the rim of a flask
into which is a small amount of ammonium hydroxide solution. Do not allow the
wire to touch the liquid -- just suspend it in the vapor.
What you will see is the catalytic oxidation of ammonia. If all goes well, the
reaction will be so exothermic that the wire will glow brighter -- sometimes
it will actually melt.
The catalyst is the platinum wire itself. The combustion reaction only can
occur when the levels of methanol and oxygen are within certain limits.
When these conditions are met, the methanol burns until either it or enough
oxygen is consumed to bring the concentrations outside these limits. Then
the combustion will not start up again until enough methanol evaporates or
oxygen diffuses back into the area around the platinum wire.
Richard E. Barrans Jr., Ph.D.
PG Research Foundation, Darien, Illinois
Click here to return to the Chemistry Archives
Update: June 2012