Explain why graphite can be used as a lubricant.

Cambridge International IGCSE Chemistry (0620) — 2.6 Giant covalent structures · Explain · 4 marks · View as Markdown

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

Graphite is a form of carbon with a giant covalent structure. It is used in industry as a dry lubricant in situations where liquid oils are unsuitable.

Model answer (4 marks)

Graphite has a layered structure of sheets of carbon atoms bonded strongly within each sheet but weakly between sheets.
The weak inter‑layer forces allow the sheets to slide over one another.
Because the layers can move easily, surfaces coated with graphite can slide past each other with little friction, making it an effective dry lubricant.

Examiner tips

Use the word "layers" and explain the weak inter‑layer forces. Show that sliding of layers reduces friction. Keep the answer concise and directly linked to the marks.
Mention that the strong covalent bonds give structural integrity while the weak forces enable movement.

Common mistakes

Confusing graphite with diamond or other allotropes. Failing to mention the weak inter‑layer forces. Giving a generic definition of lubricant without linking to graphite’s structure.

Mark scheme (4 marks)

Graphite is arranged in layers
The layers can slide over each other
The forces between layers are weak
This allows surfaces to move past each other with little friction / reducing friction between surfaces

Key terms in this question

lubricant