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Methanol vapor burning in a plastic jug

methanol burning inside plastic jug,  large blue flame

Why does the combustion of methanol produce such a large flame?

Methanol has the formula CH3OH. It is similar to methane, CH4, except a hydrogen has been replaced with -OH. Methanol is very flammable and is sometimes used as an additive in gasoline.

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pouring methanol in jug

Video for Windows

pouring methanol in jug

Quicktime

The demonstrator pours just the right amount of methanol into the jug.

swirling methanol in jug

Video for Windows
swirling methanol in jug

Quicktime

The jug is rolled in order to increase the surface area of the liquid methanol. An increased surface area speeds up the rate of vaporization. The vapor pressure of methanol is higher than that of water, so the liquid methanol enters the gaseous phase faster than water would if it were poured into the jug at the same temperature.

 

dropping burning stick in mouth of jug

Video for Windows
dropping burning stick in mouth of jug

Quicktime

The reaction takes place in the gaseous phase. In the presence of oxygen from the air, the methanol gas burns when ignited with a flame. This produces carbon dioxide and water. The intensity of the reaction is dependent upon the concentration of methanol gas.

 

This demo should only be performed using a plastic jug. The large quantities of gases (H2O and CO2) produced during the very rapid combustion could easily shatter a glass container.

 

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