Page 203 - ICSE Chemistry 8

Amorphous Forms of Carbon

The word amorphous means lacking in shape and form. The
Thirst for Knowledge
amorphous forms of carbon contain loosely held par cles and
hence have no par cular shape or structure. The amorphous form of any

The amorphous forms of carbon are charcoal, coke, gas carbon, substance is more ac ve than its
crystalline form. This is because
lampblack (carbon black or soot) and coal. These forms of
the small pieces of amorphous
carbon can be easily broken into smaller pieces and in this way
form have more surface area as
the surface area of the substance increases.
compared to crystalline form.
Charcoal

Charcoal is obtained by strongly hea ng organic ma er such as wood, bones and sugar in either the
absence of air or limited supply of air. In this process, bigger molecules break down into smaller ones and
vola le impuri es are driven off . This process is called destruc ve dis lla on.
Destruc ve dis lla on is the process in which break down of an organic substance takes place when it is
heated strongly in the absence of air. In this process, when substances with low boiling points are heated,
they escape leaving behind charcoal.

Depending upon the source used, there are three types of charcoal—wood charcoal, bone or animal
charcoal and sugar charcoal.
Wood Charcoal

Wood charcoal is black, porous and bri le solid. It is obtained by
destruc ve dis lla on of wood. During this process a mixture of
gases like carbon dioxide (CO ), carbon monoxide (CO), methane
2
(CH ) and hydrogen (H ) is also formed. This mixture is combus ble
2
4
and is known as wood gas.
In the laboratory, wood charcoal is prepared by hea ng wood
Fig. 9.7: Preparation of wood charcoal
shavings or saw dust in the absence of air. by destructive distillation of wood
Physical Properties of Wood Charcoal

-3
• The density of wood charcoal is 1.5 g cm which is greater than that of water but it fl oats on water
since it is porous. It has the capacity to hold air in its pores.
• It is a bad conductor of heat and electricity
• Wood charcoal is a good adsorbent of gases, liquids and solids. An adsorbent has the capacity to
a ract to its surface the molecules of a gas or solu on with which it is in contact.

Thirst for Knowledge

Locally, wood charcoal is prepared by piling logs of wood one above the
other with a gap in the centre of the pile. The pile is covered with wet
clay, to prevent the entry of air. A few holes are le at the bo om of the
pile. The wood is set on fi re. When the fi re dies out, wood charcoal is
obtained.

189