Graphite is used as an electrode in electrolysis experiments. Explain why graphite is able to conduct electricity, and why it has a high melting point.

OCR A-Level Chemistry B: Salters (H433) — 2.4 Electrons, bonding and structure · Explain · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Graphite is a form of carbon that is used as an electrode material in industrial electrolysis. Unlike most non-metals, graphite can conduct electricity and withstand very high temperatures.

Model answer (5 marks)

Each carbon atom in graphite is bonded to three others by covalent bonds, leaving one electron delocalised over the layer.
The delocalised electrons are free to move and carry charge, so graphite conducts electricity.
Graphite is a giant covalent structure; breaking the many strong covalent bonds requires a large amount of energy, giving it a high melting point.

Examiner tips

  • Use the term ‘delocalised electrons’ and ‘giant covalent structure’
  • Show the link between free electrons and conductivity
  • Explain that high melting point comes from many strong covalent bonds

Common mistakes

  • Confusing graphite with diamond – forgetting the delocalised electrons
  • Saying graphite conducts because it is a metal
  • Giving the wrong reason for the high melting point, e.g. ‘high temperature resistance’ instead of covalent bond energy

Mark scheme (5 marks)

  1. Each carbon atom forms three covalent bonds with three other carbon atoms
  2. This leaves one delocalised electron per carbon atom
  3. These delocalised electrons are free to move and carry charge, allowing graphite to conduct electricity
  4. Graphite is a giant covalent structure
  5. A large amount of energy is needed to break the many strong covalent bonds, giving graphite a high melting point

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