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Name: Joanne J.
Status: student
Age: 20s
Location: N/A
Country: N/A
Date: 2001 - 2002


Question:
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.


Replies:
Joanne,

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 reaction repeats.

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.

Regards,
ProfHoff 407


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.
Assistant Director
PG Research Foundation, Darien, Illinois



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