Page 23 - Curriculum Visions Dynamic Book

 A piece of activated charcoal has been dropped into a gas jar containing bromine and the cover glass replaced.
adsorb: 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.
halogen: one of a group of elements including chlorine, bromine, iodine and fluorine.
 After 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 with none remaining as free gas.
 Within a minute the colour of the gas is getting lighter as fewer free bromine molecules remain in the jar.
Activated charcoal
Activated charcoal has a very large reactive surface area (about 2000 sq m of surface area for every gram in weight of charcoal). It is able to soak up (adsorb) large numbers of gas molecules on this vast surface.
This impressive property means
that activated charcoal has been
widely used as a gas filter, from gas masks for use in war or in fire- fighting, to removing unpleasant odours. It is also used in water purification plants.
This sequence of pictures shows a gas jar, with activated
charcoal in the bottom, that has been filled with bromine, a
poisonous, brown halogen gas. The pictures were taken over a few
minutes. Notice how the amount of free bromine in the gas jar (as
seen by the colour of the gas) decreases. In the gas jar on the 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. Although activated charcoal works
well for many hydrocarbons, chlorine and similar gases, carbon will not absorb oxygen or nitrogen. Gas-suits with activated charcoal linings were used by the allied forces in the Gulf War because there was a threat from gas attack.
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