Carbon is found in organic compounds, in carbonates, etc.
Allotropic forms of carbon
Allotropy is the appearance of an element in different forms in the
same physical state.
Crystalline Allotropes
Diamond
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Graphite
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Brittle, crystalline, non-volatile, resistant to melting and chemical
attack.
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Soft, grayish-black, crystalline, soft feel and metallic luster.
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RD – 3.52, fusible, melts at 3500°C
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RD – 2.2, melts at 2527°C under pressure.
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May be colorless, blue, green, yellow, red due to impurities.
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Is grayish-black and leaves mark on paper (pencil).
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ยต = 2.5. Transparent to light and x-rays.
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Opaque to light.
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Insoluble in known reagents.
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Insoluble in known reagents.
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Good conductor of heat, not electricity.
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Good conductor of heat and electricity.
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Chemically inert.
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Is oxidized in a mixture of K2Cr2O7
and H2SO4.
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At 800°C, in O2 it is oxidized to CO2
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At 700°C, in O2 it is oxidized to CO2
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At 1500°C, O2 absent, it becomes graphite.
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Heated in absence of O2, it is stable.
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Atoms tetrahedrally arranged – rigid, compact, hard, dense, high
melting point. No free electrons to conduct electricity.
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Atoms arranged in planes – hexagonally. Planes held by weak
attraction – can slide over, soft and greasy. Free electrons to conduct
electricity.
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Amorphous Allotropes
Wood Charcoal
formed by the destructive distillation of wood – heating in the absence
of air, and collecting volatile substances – wood charcoal, pyroligneous acid,
wood tar and combustible gases are formed.
Physical properties
Physical properties
1.
Black, porous, brittle, amorphous.
2.
Can absorb gases and liquids.
3.
Insoluble in common solvents.
Chemical properties
1.
Burns at 400°C.
C + O2 → CO2
C + O2 → CO2
2.
At high temperatures, under the effect of a
catalyst, it combines with hydrogen to form methane.
C + 2H2 → CH4
C + 2H2 → CH4
3.
With sulfur vapor it forms a colorless toxic
liquid, carbon disulphide.
C + 2S → CS2
C + 2S → CS2
4.
For the extraction of metals, reducing agent.
C + ZnO → Zn + CO
C + PbO → Pb + CO
Fe2O3 + 3C
→ 2Fe
+ 3CO
5.
When heated with concentrated sulphuric acid,
charcoal reduces it.
C + 2H2SO4
→ 2H2O
+ CO2 + SO2
6.
When heated with concentrated nitric acid,
charcoal reduces it.
C + 4HNO3 → 2H2O
+ CO2 + 4NO2
7.
When steam is passed over hot charcoal water gas
is formed.
C + 2H2O → CO + H2
8.
Calcium oxide and coke form calcium carbide when
heated.
CaO + 3C → CaC2 + CO
Uses
1.
as a fuel,
2.
as an absorbing agent,
3.
in gunpowder
Lampblack
When oil is heated in insufficient air, lampblack is formed (oil
impurities can be removed by chlorine). It is used to make shoe-polish,
printers ink, carbon paper, typewriter ribbons, etc.
To show that all allotropes contain equal amounts of carbon, equal
weight are placed in trays and heated in oxygen. Carbon dioxide is absorbed by
KOH, and the increase in weight noted. It is equal for equal weights of
allotropes.
