Page 27 - Curriculum Visions Dynamic Book

adsorb/adsorption: to “collect” gas molecules
or other particles on to the surface of a substance. They are not chemically combined and can be removed. (The process is called “adsorption”.) Compare to absorb.
toxic: poisonous enough to cause death.
vapour: the gaseous form of a substance that is normally a liquid. For example, water vapour is the gaseous form of liquid water.
Activated charcoal in gas masks
Activated charcoal has a very large surface area (about 2000 sq m of surface area
for every gram in weight of charcoal). It is able to take up (adsorb) large numbers of molecules of gases onto this vast surface.
This impressive property has meant that activated charcoal is widely used as gas filters and gas masks in war.
The sequence of pictures below shows
a gas jar with activated charcoal in the bottom which has been filled with bromine, a poisonous brown halogen gas. The pictures were taken over a few minutes. The colour indicates the amount of free bromine in the gas jar. Notice that in the gas jar on the far right, there is no free bromine left at all.
Once all the sites on the activated charcoal have been used, it has to be thrown away. It cannot be reactivated.
 Gas masks contain filter pads of activated carbon. These absorb the tear or poison gas.
 Pieces of activated charcoal have been dropped into a gas jar containing bromine and the cover
glass replaced.
This sequence of photographs shows that at the end of a few minutes
the gas jar is colourless, because all of the bromine molecules are now adsorbed on to the surface of the activated charcoal.
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