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Question

A Graphite has a layer like structure.
B. The distance between two layers in graphite is 20 pm
C. Each layer is composed of planar hexagonal rings
Which of the above statement (s) is /are true?

A
A & C
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B
A & B
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C
only A
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D
A, B & C
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Solution

The correct option is A A & C
(A) Graphite has a layered structure held by van der Waals forces
(B) The distance between two layers is 340 pm.
(C) Each layer is composed of planar hexagonal rings of sp2 hybridized carbon atoms. Each C atom in hexagonal ring make three sigma bonds with three neighboring C atoms and the fourth electron forms a π bond.

THEORY
Graphite:
  • Graphite has a layered structure held by van der Waals forces and the distance between the two layers is 340 pm.
  • Each layer is composed of planar hexagonal rings of sp2 hybridized carbon atoms.
  • Each C atom in a hexagonal ring makes three sigma bonds with three neighboring C atoms and the fourth electron forms a 𝜋 bond.
  • Electrons are mobile and delocalized over the whole sheet therefore graphite conducts electricity along with the sheet.
  • Graphite cleaves easily between the layers; hence it is very soft and slippery.
  • Graphite is used as a dry lubricant in machines running at high temperatures, where oil can not be used as a lubricant.
  • Graphite is thermodynamically most stable allotrope of carbon, hence ΔHfo of graphite is taken as zero.
  • ΔHof of diamond =1.90 kJmol1
  • ΔHofof Fullerene (C60)=38.1 kJmol1
  • Other forms of elemental carbon like carbon black, coke and charcoal are all impure forms of graphite or fullerenes.
  • Carbon black is obtained by burning hydrocarbons in a limited supply of air. Charcoal and coke are obtained by heating wood or coal respectively at high temperatures in the absence of air.

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